Fenbendazole

updated

Fenbendazole is a benzimidazole carbamate anthelmintic that FDA approves as an animal drug for dogs, cattle and goats and that is not approved for use in people. Its experimental cancer use rests on cell and mouse studies with conflicting results, and no controlled human cancer study exists. Case reports describe severe liver injury after self-sourced veterinary use, and a 2025 case series of self-treating patients was retracted.

Benzimidazole carbamate anthelmintic

  • Fenbendazole is PubChem CID 3334, C15H13N3O2S, molecular weight 299.3, a benzimidazole carbamate anthelmintic also sold as Panacur and Safe-Guard.
  • FDA approves fenbendazole as an animal drug: the Panacur C Canine label is for dogs under NADA 121-473 and the Safe-Guard suspension label is for cattle and goats under NADA 128-620. An openFDA Drugs@FDA query returned no human drug application.
  • A PubMed search on 10 October 2026 for fenbendazole with human trial filters returned 3 records, none about cancer, and a ClinicalTrials.gov query returned no registered study of fenbendazole itself.
  • Cell and mouse cancer results conflict: a positive nu/nu xenograft report, no effect on EMT6 tumor growth in mice, and an effect in one SCID lymphoma model only alongside added vitamins.
  • Case reports describe severe liver injury after self-sourced veterinary fenbendazole, including histologic confirmation in one case and RUCAM scores of 8 and 9 in two others.
  • A 2025 case series of self-treating patients is marked retracted in PubMed and is not cited as support. The remission story sellers cite is a personal account, not a study.

What is fenbendazole, and what is its regulatory status?

Fenbendazole is a benzimidazole carbamate anthelmintic. FDA approves it as an animal drug for dogs, cattle and goats, and it is not approved for use in people.

Fenbendazole is PubChem CID 3334, C15H13N3O2S, molecular weight 299.3, CAS 43210-67-9, chemically methyl N-(6-phenylsulfanyl-1H-benzimidazol-2-yl)carbamate. Synonyms include Panacur, Safe-Guard and Hoe 881v. It is a single defined molecule with no salt form.

The Panacur C Canine label (Merck Animal Health, label effective 15 May 2026) is for dogs only, covers roundworms, hookworms, whipworms and tapeworms, and states approval under NADA 121-473. In US clinical studies 3 of 240 dogs (about 1%) vomited. The Safe-Guard suspension 10% label (set ID 9188886a-54bc-4c68-9f1d-37a20e031076, label effective 17 June 2026) is for beef and dairy cattle and goats under NADA 128-620 and carries withdrawal periods for meat and milk. An openFDA Drugs@FDA query for fenbendazole returned no match, so no human drug application was found. The approval status of the other labelers on DailyMed was not reviewed.

The NIDDK LiverTox entry states that fenbendazole is used mainly for worm infestations in domestic cats and dogs, is not approved for use in humans, and has been claimed to have antineoplastic activity. Because it is sold over the counter, it has been used off label for cancer. A 2024 review states that fenbendazole is not approved by FDA or EMA and that its human pharmacokinetics and safety are not well documented.

Material used for self-treatment is typically animal-grade product. DailyMed lists many fenbendazole suspensions, pastes and tablets from different labelers, and their excipients and purity are not those of any product studied in people. Oxfendazole is a different drug, related to fenbendazole by metabolism, and is not covered here.

PubChem: fenbendazole identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 3334, fenbendazole.

Fenbendazole is a benzimidazole carbamate anthelmintic, PubChem CID 3334, C15H13N3O2S, 299.3 g/mol, CAS 43210-67-9, IUPAC name methyl N-(6-phenylsulfanyl-1H-benzimidazol-2-yl)carbamate. Synonyms include Panacur, Safe-Guard and Hoe 881v. It is a single defined molecule with no salt form.

Participants / model
Chemical identity, not a clinical population
Treatment
Defined molecule
Follow-up
Not applicable
Study design
Chemical database record
Funding
not stated in the source

Identity record only. Material used for self-treatment is typically animal-grade product, and DailyMed lists many fenbendazole suspensions, pastes and tablets from different labelers whose excipients and purity are not those of any product studied in people. Oxfendazole is a different drug, related by metabolism.

Read the original source
Veterinary labels: dogs, cattle and goats; no human application found

Official label

DailyMed, National Library of Medicine. Panacur C Canine (fenbendazole) granules, Merck Animal Health, label effective 2026-05-15. Safe-Guard suspension 10% (set ID 9188886a-54bc-4c68-9f1d-37a20e031076), label effective 2026-06-17. openFDA Drugs@FDA query for fenbendazole, run 10 October 2026.

FDA approves fenbendazole as an animal drug. The Panacur C Canine label (Merck Animal Health, label effective 15 May 2026) is for dogs only, covers roundworms, hookworms, whipworms and tapeworms, and states approval under NADA 121-473. In US clinical studies 3 of 240 dogs (about 1%) vomited. The Safe-Guard suspension 10% label (set ID 9188886a-54bc-4c68-9f1d-37a20e031076, label effective 17 June 2026) is for beef and dairy cattle and goats under NADA 128-620 and carries withdrawal periods for meat and milk. An openFDA Drugs@FDA query for fenbendazole returned no match, so no human drug application was found. Approval status of the other labelers on DailyMed was not reviewed.

Participants / model
Dogs; cattle and goats
Treatment
Oral granules; oral suspension
Follow-up
Label versions effective 15 May 2026 and 17 June 2026
Study design
Veterinary labels plus a regulatory database query
Funding
not stated in the source

Veterinary labels only. They are not human prescribing information and give no basis for human use. Label dosing is not reproduced on this page.

Read the original source
LiverTox: not approved for humans; acute liver injury possible

Regulatory record

Hoofnagle JH. Fenbendazole. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2012. PMID 42081641.

The entry states that fenbendazole is used mainly for worm infestations in domestic cats and dogs, is not approved for use in humans, and has been claimed to have antineoplastic activity, and that because it is sold over the counter it has been used off label for cancer. It states that therapy is commonly associated with mild and transient serum enzyme elevations and can also lead to clinically apparent acute liver injury.

Participants / model
Humans, summary of the case literature
Treatment
Oral veterinary product
Follow-up
Not applicable
Study design
NIH drug-induced liver injury reference (LiverTox)
Funding
not stated in the source

Summary of the case literature. The record reviewed gives no incidence figure.

Read the original source
3 trial-type records, none about cancer; no registered fenbendazole study

PubMed search record

PubMed search for fenbendazole AND humans[mh] AND (randomized controlled trial[pt] OR clinical trial[pt] OR controlled clinical trial[pt]), run 10 October 2026. ClinicalTrials.gov query for fenbendazole and a PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin, both run the same day.

A PubMed search on 10 October 2026 for fenbendazole in humans with randomized controlled trial, clinical trial or controlled clinical trial publication types returned 3 records: two anthelmintic reports from 1976 and 1980 (PMIDs 779682 and 7010692) and a 2026 oxfendazole pharmacokinetic paper (PMID 41662151). None concerned cancer. The 1976 trial gave single doses per person against intestinal worms, reporting effectiveness against Ascaris, substantial egg count reductions for hookworm and good results against Trichuris at the higher dose, and its abstract reports no safety outcome. A ClinicalTrials.gov query for fenbendazole the same day returned 9 records: 5 oxfendazole studies and 4 unrelated studies, so no registered study of fenbendazole itself and no registered cancer trial. No human pharmacokinetics of fenbendazole given as itself were found; the closest is a healthy-adult oxfendazole study (PMID 33526484) that modeled fenbendazole as a metabolite. A 2024 review (PMID 39197912) states that fenbendazole is not approved by FDA or EMA and that its human pharmacokinetics and safety are not well documented. A PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin returned 1 record, a honey bee paper.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Searches run on 10 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 10 October 2026, not proof that no unpublished work exists. Oxfendazole is a separate drug and is not cited as fenbendazole evidence.

Read the original source

What have the cell and animal studies found?

The results conflict. One report found fenbendazole cytotoxic to human cancer cells and blocking human xenograft growth in nu/nu mice, while it did not change EMT6 tumor growth in mice, and an effect in one SCID lymphoma model appeared only alongside added vitamins. All of this is in cells and mice, and no controlled human cancer study exists.

One preclinical report found that fenbendazole showed moderate affinity for mammalian tubulin and was cytotoxic to human cancer cells at micromolar concentrations. It caused mitochondrial translocation of p53 and inhibited glucose uptake, GLUT transporter expression and hexokinase II. Fed orally to nu/nu mice, it blocked the growth of human xenografts. The abstract gives no dose, tumor type or effect size.

In EMT6 mouse mammary tumor cells, intensive fenbendazole was toxic in vitro, more so under severe hypoxia, and additive with radiation or docetaxel. Maximally intensive regimens did not alter EMT6 tumor growth in mice or add to radiation, and the authors report no evidence that it has value in cancer therapy. In a separate study, a 150 ppm fenbendazole diet did not change EMT6 tumor growth, invasion or metastasis in BALB/c mice.

In SCID mice with a human lymphoma xenograft (20 mice, 4 diet groups), neither fenbendazole alone nor supplementary vitamins alone changed tumor growth, but the two together significantly inhibited it. The authors call the mechanism unknown, and the abstract does not name which vitamins. It is one small study with no berberine or cannabidiol arm, and it is the only experimental link in the records reviewed to the vitamin part of self-treatment protocols.

Cells and nu/nu mice: tubulin, p53, glucose uptake, xenograft growth

Animal study

Dogra N et al. Sci Rep. 2018;8(1):11926. PMID 30093705.

Fenbendazole showed moderate affinity for mammalian tubulin and was cytotoxic to human cancer cells at micromolar concentrations. It caused mitochondrial translocation of p53 and inhibited glucose uptake, GLUT transporter expression and hexokinase II. Fed orally to nu/nu mice, it blocked the growth of human xenografts. The abstract gives no dose, tumor type or effect size.

Participants / model
Human cancer cell lines; nu/nu mice with human xenografts
Treatment
Fenbendazole in cell culture; oral feeding in mice; dose not stated in the abstract
Follow-up
not stated in the source
Study design
Original preclinical study, cell culture and mouse xenografts
Funding
not stated in the source

Cells and mice only. The abstract gives no dose, tumor type or effect size, and the later mouse studies below did not all agree with it.

Read the original source
EMT6 cells toxic in vitro; no change in EMT6 tumor growth in mice

Animal study

Duan Q et al. Anticancer Res. 2013;33(2):355-62. PMID 23393324.

In EMT6 mouse mammary tumor cells, intensive fenbendazole was toxic in vitro (more so under severe hypoxia) and additive with radiation or docetaxel. Maximally intensive regimens did not alter EMT6 tumor growth in mice or add to radiation, and the authors report no evidence that it has value in cancer therapy.

Participants / model
EMT6 mouse mammary tumor cells; mice with EMT6 tumors
Treatment
Fenbendazole in cell culture and in mice, alone and with radiation or docetaxel; dose and route not stated in the source
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

A negative tumor-growth result in mice.

Read the original source
150 ppm fenbendazole diet: no change in EMT6 tumors in BALB/c mice

Animal study

Duan Q et al. J Am Assoc Lab Anim Sci. 2012;51(2):224-30. PMID 22776123.

A 150 ppm fenbendazole diet did not change EMT6 tumor growth, invasion or metastasis in BALB/c mice.

Participants / model
BALB/c mice with EMT6 mammary tumors
Treatment
Fenbendazole at 150 ppm in the diet
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

A negative result in mice. Dietary ppm in mice does not convert to a human dose.

Read the original source
20 SCID mice, 4 diet groups: effect only with fenbendazole plus vitamins

Animal study

Gao P et al. J Am Assoc Lab Anim Sci. 2008;47(6):37-40. PMID 19049251.

In SCID mice with a human lymphoma xenograft (20 mice, 4 diet groups), neither fenbendazole alone nor supplementary vitamins alone changed tumor growth, but the two together significantly inhibited it. The authors call the mechanism unknown, and the abstract does not name which vitamins.

Participants / model
20 SCID mice with a human lymphoma xenograft
Treatment
Four diet groups, including fenbendazole alone, supplementary vitamins alone and both together; doses not stated in the source
Follow-up
not stated in the source
Study design
Controlled preclinical study
Funding
not stated in the source

One small SCID study with no berberine or cannabidiol arm. It is the only experimental link in the records reviewed to the vitamin part of self-treatment protocols.

Read the original source

Has fenbendazole been tested in people?

Not for cancer. A PubMed search on 10 October 2026 for fenbendazole with human trial filters returned 3 records, none about cancer, and a ClinicalTrials.gov query returned no registered study of fenbendazole itself. No human pharmacokinetics of fenbendazole given as itself were found.

A PubMed search on 10 October 2026 for fenbendazole in humans with randomized controlled trial, clinical trial or controlled clinical trial publication types returned 3 records: two anthelmintic reports from 1976 and 1980 and a 2026 oxfendazole pharmacokinetic paper. None concerned cancer. The 1976 trial gave single doses against intestinal worms and reported effectiveness against Ascaris, substantial egg count reductions for hookworm and good results against Trichuris at the higher dose. Its abstract reports no safety outcome.

A ClinicalTrials.gov query for fenbendazole on the same day returned 9 records: 5 oxfendazole studies and 4 unrelated studies. That means no registered study of fenbendazole itself and no registered cancer trial.

No human pharmacokinetics of fenbendazole given as itself were found. The closest is a healthy-adult study of oxfendazole, a different drug, that modeled fenbendazole as one of its metabolites. A 2024 review states that fenbendazole's human pharmacokinetics and safety are not well documented.

3 trial-type records, none about cancer; no registered fenbendazole study

PubMed search record

PubMed search for fenbendazole AND humans[mh] AND (randomized controlled trial[pt] OR clinical trial[pt] OR controlled clinical trial[pt]), run 10 October 2026. ClinicalTrials.gov query for fenbendazole and a PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin, both run the same day.

A PubMed search on 10 October 2026 for fenbendazole in humans with randomized controlled trial, clinical trial or controlled clinical trial publication types returned 3 records: two anthelmintic reports from 1976 and 1980 (PMIDs 779682 and 7010692) and a 2026 oxfendazole pharmacokinetic paper (PMID 41662151). None concerned cancer. The 1976 trial gave single doses per person against intestinal worms, reporting effectiveness against Ascaris, substantial egg count reductions for hookworm and good results against Trichuris at the higher dose, and its abstract reports no safety outcome. A ClinicalTrials.gov query for fenbendazole the same day returned 9 records: 5 oxfendazole studies and 4 unrelated studies, so no registered study of fenbendazole itself and no registered cancer trial. No human pharmacokinetics of fenbendazole given as itself were found; the closest is a healthy-adult oxfendazole study (PMID 33526484) that modeled fenbendazole as a metabolite. A 2024 review (PMID 39197912) states that fenbendazole is not approved by FDA or EMA and that its human pharmacokinetics and safety are not well documented. A PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin returned 1 record, a honey bee paper.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Searches run on 10 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 10 October 2026, not proof that no unpublished work exists. Oxfendazole is a separate drug and is not cited as fenbendazole evidence.

Read the original source

Do the claims sellers make about fenbendazole hold up?

The antiparasitic use is real in animals under veterinary labels. The experimental oncology label is accurate only as a description of cell and animal studies with conflicting results, and neither the remission story sellers cite nor the protocols that pair fenbendazole with vitamin E succinate, berberine and CBD has controlled evidence behind it in the records reviewed.

Sellers describe fenbendazole as an antiparasitic with experimental oncology uses, made well known by the Joe Tippens remission story and by self-treatment protocols that pair it with vitamin E succinate, berberine and CBD. The antiparasitic use is real in animals under the veterinary labels described above, and a 1976 human trial of single doses against intestinal worms exists.

The remission story is a personal account that sellers cite. It is not a study: a PubMed query for Tippens and fenbendazole on 10 October 2026 returned 0 records. A 2025 case series of self-treating patients is marked RETRACTED ARTICLE in PubMed, with a retraction notice in Case Rep Oncol, 2026 Jan 21;19(1):169, and it is not cited here as support for any outcome. Self-reports with other treatments and no control cannot show that any drug caused a tumor response.

The combination protocols have no study behind them in the records reviewed. A PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin returned 1 record, a honey bee paper. The only experimental link to the vitamin part is the small SCID lymphoma study described above, which did not name the vitamins and had no berberine or cannabidiol arm.

Retracted case series; Tippens query returned 0 records

Case report

Makis W et al. Case Rep Oncol. 2025;18(1):856-863. PMID 40605964.

A 2025 case series of self-treating patients is marked RETRACTED ARTICLE in PubMed, with a retraction notice in Case Rep Oncol, 2026 Jan 21;19(1):169. It is not cited as support for any outcome. The remission story that sellers cite is a personal account, not a study: a PubMed query for Tippens AND fenbendazole run on 10 October 2026 returned 0 records.

Participants / model
Adults who self-treated, per a retracted report
Treatment
Not reproduced because the report is retracted
Follow-up
Not applicable
Study design
Retracted case series; a personal account that is not a study
Funding
not stated in the source

Retracted, so it cannot be cited as support. Self-reports with other treatments and no control cannot show that any drug caused a tumor response.

Read the original source
3 trial-type records, none about cancer; no registered fenbendazole study

PubMed search record

PubMed search for fenbendazole AND humans[mh] AND (randomized controlled trial[pt] OR clinical trial[pt] OR controlled clinical trial[pt]), run 10 October 2026. ClinicalTrials.gov query for fenbendazole and a PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin, both run the same day.

A PubMed search on 10 October 2026 for fenbendazole in humans with randomized controlled trial, clinical trial or controlled clinical trial publication types returned 3 records: two anthelmintic reports from 1976 and 1980 (PMIDs 779682 and 7010692) and a 2026 oxfendazole pharmacokinetic paper (PMID 41662151). None concerned cancer. The 1976 trial gave single doses per person against intestinal worms, reporting effectiveness against Ascaris, substantial egg count reductions for hookworm and good results against Trichuris at the higher dose, and its abstract reports no safety outcome. A ClinicalTrials.gov query for fenbendazole the same day returned 9 records: 5 oxfendazole studies and 4 unrelated studies, so no registered study of fenbendazole itself and no registered cancer trial. No human pharmacokinetics of fenbendazole given as itself were found; the closest is a healthy-adult oxfendazole study (PMID 33526484) that modeled fenbendazole as a metabolite. A 2024 review (PMID 39197912) states that fenbendazole is not approved by FDA or EMA and that its human pharmacokinetics and safety are not well documented. A PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin returned 1 record, a honey bee paper.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Searches run on 10 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 10 October 2026, not proof that no unpublished work exists. Oxfendazole is a separate drug and is not cited as fenbendazole evidence.

Read the original source
20 SCID mice, 4 diet groups: effect only with fenbendazole plus vitamins

Animal study

Gao P et al. J Am Assoc Lab Anim Sci. 2008;47(6):37-40. PMID 19049251.

In SCID mice with a human lymphoma xenograft (20 mice, 4 diet groups), neither fenbendazole alone nor supplementary vitamins alone changed tumor growth, but the two together significantly inhibited it. The authors call the mechanism unknown, and the abstract does not name which vitamins.

Participants / model
20 SCID mice with a human lymphoma xenograft
Treatment
Four diet groups, including fenbendazole alone, supplementary vitamins alone and both together; doses not stated in the source
Follow-up
not stated in the source
Study design
Controlled preclinical study
Funding
not stated in the source

One small SCID study with no berberine or cannabidiol arm. It is the only experimental link in the records reviewed to the vitamin part of self-treatment protocols.

Read the original source
Veterinary labels: dogs, cattle and goats; no human application found

Official label

DailyMed, National Library of Medicine. Panacur C Canine (fenbendazole) granules, Merck Animal Health, label effective 2026-05-15. Safe-Guard suspension 10% (set ID 9188886a-54bc-4c68-9f1d-37a20e031076), label effective 2026-06-17. openFDA Drugs@FDA query for fenbendazole, run 10 October 2026.

FDA approves fenbendazole as an animal drug. The Panacur C Canine label (Merck Animal Health, label effective 15 May 2026) is for dogs only, covers roundworms, hookworms, whipworms and tapeworms, and states approval under NADA 121-473. In US clinical studies 3 of 240 dogs (about 1%) vomited. The Safe-Guard suspension 10% label (set ID 9188886a-54bc-4c68-9f1d-37a20e031076, label effective 17 June 2026) is for beef and dairy cattle and goats under NADA 128-620 and carries withdrawal periods for meat and milk. An openFDA Drugs@FDA query for fenbendazole returned no match, so no human drug application was found. Approval status of the other labelers on DailyMed was not reviewed.

Participants / model
Dogs; cattle and goats
Treatment
Oral granules; oral suspension
Follow-up
Label versions effective 15 May 2026 and 17 June 2026
Study design
Veterinary labels plus a regulatory database query
Funding
not stated in the source

Veterinary labels only. They are not human prescribing information and give no basis for human use. Label dosing is not reproduced on this page.

Read the original source

How does fenbendazole act in cells and animals?

In cell and mouse studies fenbendazole bound mammalian tubulin with moderate affinity, was cytotoxic to human cancer cells at micromolar concentrations, and affected p53 localization and glucose handling. Whether any of this happens in people is unknown, because no human study measured it.

In one preclinical report, fenbendazole showed moderate affinity for mammalian tubulin and was cytotoxic to human cancer cells at micromolar concentrations. It caused mitochondrial translocation of p53 and inhibited glucose uptake, GLUT transporter expression and hexokinase II.

In EMT6 mouse mammary tumor cells, intensive fenbendazole was toxic in vitro, more so under severe hypoxia, and additive with radiation or docetaxel. Maximally intensive regimens did not alter EMT6 tumor growth in mice. No human pharmacokinetic study of fenbendazole given as itself exists, so exposure in people is not established.

Cells and nu/nu mice: tubulin, p53, glucose uptake, xenograft growth

Animal study

Dogra N et al. Sci Rep. 2018;8(1):11926. PMID 30093705.

Fenbendazole showed moderate affinity for mammalian tubulin and was cytotoxic to human cancer cells at micromolar concentrations. It caused mitochondrial translocation of p53 and inhibited glucose uptake, GLUT transporter expression and hexokinase II. Fed orally to nu/nu mice, it blocked the growth of human xenografts. The abstract gives no dose, tumor type or effect size.

Participants / model
Human cancer cell lines; nu/nu mice with human xenografts
Treatment
Fenbendazole in cell culture; oral feeding in mice; dose not stated in the abstract
Follow-up
not stated in the source
Study design
Original preclinical study, cell culture and mouse xenografts
Funding
not stated in the source

Cells and mice only. The abstract gives no dose, tumor type or effect size, and the later mouse studies below did not all agree with it.

Read the original source
EMT6 cells toxic in vitro; no change in EMT6 tumor growth in mice

Animal study

Duan Q et al. Anticancer Res. 2013;33(2):355-62. PMID 23393324.

In EMT6 mouse mammary tumor cells, intensive fenbendazole was toxic in vitro (more so under severe hypoxia) and additive with radiation or docetaxel. Maximally intensive regimens did not alter EMT6 tumor growth in mice or add to radiation, and the authors report no evidence that it has value in cancer therapy.

Participants / model
EMT6 mouse mammary tumor cells; mice with EMT6 tumors
Treatment
Fenbendazole in cell culture and in mice, alone and with radiation or docetaxel; dose and route not stated in the source
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

A negative tumor-growth result in mice.

Read the original source
3 trial-type records, none about cancer; no registered fenbendazole study

PubMed search record

PubMed search for fenbendazole AND humans[mh] AND (randomized controlled trial[pt] OR clinical trial[pt] OR controlled clinical trial[pt]), run 10 October 2026. ClinicalTrials.gov query for fenbendazole and a PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin, both run the same day.

A PubMed search on 10 October 2026 for fenbendazole in humans with randomized controlled trial, clinical trial or controlled clinical trial publication types returned 3 records: two anthelmintic reports from 1976 and 1980 (PMIDs 779682 and 7010692) and a 2026 oxfendazole pharmacokinetic paper (PMID 41662151). None concerned cancer. The 1976 trial gave single doses per person against intestinal worms, reporting effectiveness against Ascaris, substantial egg count reductions for hookworm and good results against Trichuris at the higher dose, and its abstract reports no safety outcome. A ClinicalTrials.gov query for fenbendazole the same day returned 9 records: 5 oxfendazole studies and 4 unrelated studies, so no registered study of fenbendazole itself and no registered cancer trial. No human pharmacokinetics of fenbendazole given as itself were found; the closest is a healthy-adult oxfendazole study (PMID 33526484) that modeled fenbendazole as a metabolite. A 2024 review (PMID 39197912) states that fenbendazole is not approved by FDA or EMA and that its human pharmacokinetics and safety are not well documented. A PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin returned 1 record, a honey bee paper.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Searches run on 10 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 10 October 2026, not proof that no unpublished work exists. Oxfendazole is a separate drug and is not cited as fenbendazole evidence.

Read the original source

What is known about the safety of fenbendazole?

Case reports describe severe liver injury after self-sourced veterinary fenbendazole, LiverTox lists clinically apparent acute liver injury, and a rat study points to liver tumor promotion. No human safety study exists, and human pharmacokinetics are not established.

The NIDDK LiverTox entry states that fenbendazole therapy is commonly associated with mild and transient serum enzyme elevations and can also lead to clinically apparent acute liver injury.

Two case reports describe hepatocellular injury after self-sourced use. A 67-year-old woman with 2 weeks of jaundice after self-administering fenbendazole had histologically confirmed severe hepatocellular drug-induced liver injury, with liver tests normal 3 months after stopping. A 65-year-old man with prostate cancer took veterinary fenbendazole and ivermectin for 3 months and presented with jaundice and abdominal pain, with ALT 1764 U/L, AST 1132 U/L, total bilirubin 12.9 mg/dL and R-value 37.50, and viral, autoimmune and biliary causes ruled out. Transaminases fell 58% within 9 days and normalized within 6 weeks after both agents were stopped. The RUCAM score was 9 (highly probable) for the pair, so fenbendazole cannot be separated from ivermectin in that case.

Further reports involve patients on immune checkpoint inhibitors, where attribution is hard. An 80-year-old woman with advanced non-small cell lung cancer on pembrolizumab had severe liver injury 9 months after starting it, after one month of fenbendazole taken on social media information; the dysfunction resolved spontaneously after she stopped, and she had no tumor shrinkage. A 47-year-old woman with metastatic colon cancer on nivolumab and relatlimab had severe hepatocellular injury after raising her fenbendazole dose, with RUCAM 8 (probable), quick biochemical improvement after stopping and safe reintroduction of immunotherapy. A Norwegian case report with an English abstract (PMID 41097960) describes a cancer patient admitted two weeks after immunotherapy with a tenfold rise in cholestatic parameters, and normal ASAT, ALAT, bilirubin and INR, who had taken fenbendazole the week before; biopsy showed lobular and portal inflammation and values fell spontaneously within two weeks. A further report (PMID 42383214) describes fenbendazole-associated liver injury with TUDCA taken as an intended hepatoprotective, and its abstract gives no clinical details. All of these are single case reports.

In 70 male F344 rats given a single intraperitoneal injection of 100 mg/kg diethylnitrosamine (DEN) or vehicle and then fenbendazole in the diet at 3,600 to 70 ppm for 8 weeks, relative liver weight rose and periportal hepatocellular hypertrophy appeared at 600 ppm and above, with or without DEN, and CYP1A2, 2B1 and 4A1 were induced. After DEN, connexin 32 fell and GST-P positive cells rose at 1,800 and 3,600 ppm, and the authors conclude that fenbendazole may be a liver tumor promoter. A 2007 review of rodent studies states that lifetime rat studies show it is not a carcinogen but may act as a tumor promoter after certain initiators. Dietary ppm in rats does not convert to a human dose.

LiverTox: not approved for humans; acute liver injury possible

Regulatory record

Hoofnagle JH. Fenbendazole. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2012. PMID 42081641.

The entry states that fenbendazole is used mainly for worm infestations in domestic cats and dogs, is not approved for use in humans, and has been claimed to have antineoplastic activity, and that because it is sold over the counter it has been used off label for cancer. It states that therapy is commonly associated with mild and transient serum enzyme elevations and can also lead to clinically apparent acute liver injury.

Participants / model
Humans, summary of the case literature
Treatment
Oral veterinary product
Follow-up
Not applicable
Study design
NIH drug-induced liver injury reference (LiverTox)
Funding
not stated in the source

Summary of the case literature. The record reviewed gives no incidence figure.

Read the original source
Case report: 67-year-old woman, jaundice, histologically confirmed injury

Case report

Thakurdesai A et al. ACG Case Rep J. 2024;11(5):e01354. PMID 38706451.

A 67-year-old woman with 2 weeks of jaundice after self-administering fenbendazole had histologically confirmed severe hepatocellular drug-induced liver injury, with liver tests normal 3 months after stopping.

Participants / model
A 67-year-old woman
Treatment
Self-administered veterinary fenbendazole
Follow-up
2 weeks of jaundice before presentation; liver tests normal 3 months after stopping
Study design
Single case report
Funding
not stated in the source

A single case with histologic confirmation. It shows what happened to one person, not how often this happens.

Read the original source
Case report: 65-year-old man, ALT 1764 U/L, RUCAM 9 for the pair

Case report

Powderly GE et al. Cureus. 2026;18(5):e108896. PMID 42299164.

A 65-year-old man with prostate cancer took veterinary fenbendazole and ivermectin for 3 months and presented with jaundice and abdominal pain: ALT 1764 U/L, AST 1132 U/L, total bilirubin 12.9 mg/dL and R-value 37.50, with viral, autoimmune and biliary causes ruled out. Transaminases fell 58% within 9 days and normalized within 6 weeks after both agents were stopped, and the RUCAM score was 9 (highly probable) for the pair.

Participants / model
A 65-year-old man with prostate cancer
Treatment
Self-administered veterinary fenbendazole and ivermectin
Follow-up
3 months of use; transaminases normalized within 6 weeks of stopping
Study design
Single case report
Funding
not stated in the source

Fenbendazole cannot be separated from ivermectin in this case, because the RUCAM score applies to the pair.

Read the original source
Case report: 80-year-old woman on pembrolizumab, spontaneous recovery

Case report

Yamaguchi T et al. Case Rep Oncol. 2021;14(2):886-891. PMID 34248555.

An 80-year-old woman with advanced non-small cell lung cancer on pembrolizumab had severe liver injury 9 months after starting it, after one month of fenbendazole taken on social media information. The dysfunction resolved spontaneously after she stopped, and she had no tumor shrinkage.

Participants / model
An 80-year-old woman with advanced non-small cell lung cancer on pembrolizumab
Treatment
Self-administered veterinary fenbendazole alongside pembrolizumab
Follow-up
One month of fenbendazole; injury 9 months after starting pembrolizumab
Study design
Single case report
Funding
not stated in the source

Attribution is hard because she was also on an immune checkpoint inhibitor.

Read the original source
Case report: 47-year-old woman on nivolumab and relatlimab, RUCAM 8

Case report

Krishnan A et al. World J Clin Cases. 2026;14(2):116700. PMID 41608149.

A 47-year-old woman with metastatic colon cancer on nivolumab and relatlimab had severe hepatocellular injury after raising her fenbendazole dose, with RUCAM 8 (probable), quick biochemical improvement after stopping and safe reintroduction of immunotherapy.

Participants / model
A 47-year-old woman with metastatic colon cancer on nivolumab and relatlimab
Treatment
Self-administered veterinary fenbendazole alongside immunotherapy
Follow-up
not stated in the source
Study design
Single case report
Funding
not stated in the source

Attribution is hard because she was also on immune checkpoint inhibitors.

Read the original source
70 F344 rats, 8 weeks: liver hypertrophy, CYP induction, possible tumor promoter

Animal study

Shoda T et al. Toxicol Pathol. 1999;27(5):553-62. PMID 10528635.

In 70 male F344 rats given a single intraperitoneal injection of 100 mg/kg diethylnitrosamine (DEN) or vehicle and then fenbendazole in the diet at 3,600 to 70 ppm for 8 weeks, relative liver weight rose and periportal hepatocellular hypertrophy appeared at 600 ppm and above with or without DEN, and CYP1A2, 2B1 and 4A1 were induced. After DEN, connexin 32 fell and GST-P positive cells rose at 1,800 and 3,600 ppm, and the authors conclude that fenbendazole may be a liver tumor promoter.

Participants / model
70 male F344 rats
Treatment
A single intraperitoneal injection of 100 mg/kg diethylnitrosamine or vehicle, then fenbendazole in the diet at 3,600 to 70 ppm
Follow-up
8 weeks of dietary fenbendazole
Study design
Controlled toxicology study
Funding
not stated in the source

Rats only. Dietary ppm in rats does not convert to a human dose.

Read the original source
2007 review: not a carcinogen in lifetime rat studies, possible tumor promoter

Animal study

Villar D et al. J Am Assoc Lab Anim Sci. 2007;46(6):8-15. PMID 17994667.

A 2007 review of rodent studies states that lifetime rat studies show fenbendazole is not a carcinogen but may act as a tumor promoter after certain initiators.

Participants / model
Rodent literature
Treatment
not stated in the source
Follow-up
not stated in the source
Study design
Review of rodent studies
Funding
not stated in the source

A rodent review, not human data.

Read the original source

Why does fenbendazole sit in F tier?

F fits documented human harm with no human efficacy data. Case reports describe liver injury after self-sourced use, LiverTox lists clinically apparent acute liver injury and a rat study points to tumor promotion, while the cancer rationale rests on conflicting cell and mouse results, no controlled human cancer study and a retracted case series.

No human approval exists. The cancer rationale rests on cell and mouse work that conflicts: a positive nu/nu xenograft report, no effect on EMT6 tumors in mice, and an effect in one SCID model only alongside added vitamins. There is no controlled human cancer study and no registered study of fenbendazole itself, and a 2025 case series of self-treating patients was retracted.

Against that, case reports describe liver injury after self-sourced use, including histologic confirmation in one and RUCAM scores of 8 and 9 in two others, LiverTox lists clinically apparent acute liver injury, and a rat study points to tumor promotion in the liver. That is documented human harm with no human efficacy data.

LiverTox: not approved for humans; acute liver injury possible

Regulatory record

Hoofnagle JH. Fenbendazole. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2012. PMID 42081641.

The entry states that fenbendazole is used mainly for worm infestations in domestic cats and dogs, is not approved for use in humans, and has been claimed to have antineoplastic activity, and that because it is sold over the counter it has been used off label for cancer. It states that therapy is commonly associated with mild and transient serum enzyme elevations and can also lead to clinically apparent acute liver injury.

Participants / model
Humans, summary of the case literature
Treatment
Oral veterinary product
Follow-up
Not applicable
Study design
NIH drug-induced liver injury reference (LiverTox)
Funding
not stated in the source

Summary of the case literature. The record reviewed gives no incidence figure.

Read the original source
Case report: 67-year-old woman, jaundice, histologically confirmed injury

Case report

Thakurdesai A et al. ACG Case Rep J. 2024;11(5):e01354. PMID 38706451.

A 67-year-old woman with 2 weeks of jaundice after self-administering fenbendazole had histologically confirmed severe hepatocellular drug-induced liver injury, with liver tests normal 3 months after stopping.

Participants / model
A 67-year-old woman
Treatment
Self-administered veterinary fenbendazole
Follow-up
2 weeks of jaundice before presentation; liver tests normal 3 months after stopping
Study design
Single case report
Funding
not stated in the source

A single case with histologic confirmation. It shows what happened to one person, not how often this happens.

Read the original source
Case report: 65-year-old man, ALT 1764 U/L, RUCAM 9 for the pair

Case report

Powderly GE et al. Cureus. 2026;18(5):e108896. PMID 42299164.

A 65-year-old man with prostate cancer took veterinary fenbendazole and ivermectin for 3 months and presented with jaundice and abdominal pain: ALT 1764 U/L, AST 1132 U/L, total bilirubin 12.9 mg/dL and R-value 37.50, with viral, autoimmune and biliary causes ruled out. Transaminases fell 58% within 9 days and normalized within 6 weeks after both agents were stopped, and the RUCAM score was 9 (highly probable) for the pair.

Participants / model
A 65-year-old man with prostate cancer
Treatment
Self-administered veterinary fenbendazole and ivermectin
Follow-up
3 months of use; transaminases normalized within 6 weeks of stopping
Study design
Single case report
Funding
not stated in the source

Fenbendazole cannot be separated from ivermectin in this case, because the RUCAM score applies to the pair.

Read the original source
70 F344 rats, 8 weeks: liver hypertrophy, CYP induction, possible tumor promoter

Animal study

Shoda T et al. Toxicol Pathol. 1999;27(5):553-62. PMID 10528635.

In 70 male F344 rats given a single intraperitoneal injection of 100 mg/kg diethylnitrosamine (DEN) or vehicle and then fenbendazole in the diet at 3,600 to 70 ppm for 8 weeks, relative liver weight rose and periportal hepatocellular hypertrophy appeared at 600 ppm and above with or without DEN, and CYP1A2, 2B1 and 4A1 were induced. After DEN, connexin 32 fell and GST-P positive cells rose at 1,800 and 3,600 ppm, and the authors conclude that fenbendazole may be a liver tumor promoter.

Participants / model
70 male F344 rats
Treatment
A single intraperitoneal injection of 100 mg/kg diethylnitrosamine or vehicle, then fenbendazole in the diet at 3,600 to 70 ppm
Follow-up
8 weeks of dietary fenbendazole
Study design
Controlled toxicology study
Funding
not stated in the source

Rats only. Dietary ppm in rats does not convert to a human dose.

Read the original source
3 trial-type records, none about cancer; no registered fenbendazole study

PubMed search record

PubMed search for fenbendazole AND humans[mh] AND (randomized controlled trial[pt] OR clinical trial[pt] OR controlled clinical trial[pt]), run 10 October 2026. ClinicalTrials.gov query for fenbendazole and a PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin, both run the same day.

A PubMed search on 10 October 2026 for fenbendazole in humans with randomized controlled trial, clinical trial or controlled clinical trial publication types returned 3 records: two anthelmintic reports from 1976 and 1980 (PMIDs 779682 and 7010692) and a 2026 oxfendazole pharmacokinetic paper (PMID 41662151). None concerned cancer. The 1976 trial gave single doses per person against intestinal worms, reporting effectiveness against Ascaris, substantial egg count reductions for hookworm and good results against Trichuris at the higher dose, and its abstract reports no safety outcome. A ClinicalTrials.gov query for fenbendazole the same day returned 9 records: 5 oxfendazole studies and 4 unrelated studies, so no registered study of fenbendazole itself and no registered cancer trial. No human pharmacokinetics of fenbendazole given as itself were found; the closest is a healthy-adult oxfendazole study (PMID 33526484) that modeled fenbendazole as a metabolite. A 2024 review (PMID 39197912) states that fenbendazole is not approved by FDA or EMA and that its human pharmacokinetics and safety are not well documented. A PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin returned 1 record, a honey bee paper.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Searches run on 10 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 10 October 2026, not proof that no unpublished work exists. Oxfendazole is a separate drug and is not cited as fenbendazole evidence.

Read the original source
Cells and nu/nu mice: tubulin, p53, glucose uptake, xenograft growth

Animal study

Dogra N et al. Sci Rep. 2018;8(1):11926. PMID 30093705.

Fenbendazole showed moderate affinity for mammalian tubulin and was cytotoxic to human cancer cells at micromolar concentrations. It caused mitochondrial translocation of p53 and inhibited glucose uptake, GLUT transporter expression and hexokinase II. Fed orally to nu/nu mice, it blocked the growth of human xenografts. The abstract gives no dose, tumor type or effect size.

Participants / model
Human cancer cell lines; nu/nu mice with human xenografts
Treatment
Fenbendazole in cell culture; oral feeding in mice; dose not stated in the abstract
Follow-up
not stated in the source
Study design
Original preclinical study, cell culture and mouse xenografts
Funding
not stated in the source

Cells and mice only. The abstract gives no dose, tumor type or effect size, and the later mouse studies below did not all agree with it.

Read the original source
EMT6 cells toxic in vitro; no change in EMT6 tumor growth in mice

Animal study

Duan Q et al. Anticancer Res. 2013;33(2):355-62. PMID 23393324.

In EMT6 mouse mammary tumor cells, intensive fenbendazole was toxic in vitro (more so under severe hypoxia) and additive with radiation or docetaxel. Maximally intensive regimens did not alter EMT6 tumor growth in mice or add to radiation, and the authors report no evidence that it has value in cancer therapy.

Participants / model
EMT6 mouse mammary tumor cells; mice with EMT6 tumors
Treatment
Fenbendazole in cell culture and in mice, alone and with radiation or docetaxel; dose and route not stated in the source
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

A negative tumor-growth result in mice.

Read the original source
20 SCID mice, 4 diet groups: effect only with fenbendazole plus vitamins

Animal study

Gao P et al. J Am Assoc Lab Anim Sci. 2008;47(6):37-40. PMID 19049251.

In SCID mice with a human lymphoma xenograft (20 mice, 4 diet groups), neither fenbendazole alone nor supplementary vitamins alone changed tumor growth, but the two together significantly inhibited it. The authors call the mechanism unknown, and the abstract does not name which vitamins.

Participants / model
20 SCID mice with a human lymphoma xenograft
Treatment
Four diet groups, including fenbendazole alone, supplementary vitamins alone and both together; doses not stated in the source
Follow-up
not stated in the source
Study design
Controlled preclinical study
Funding
not stated in the source

One small SCID study with no berberine or cannabidiol arm. It is the only experimental link in the records reviewed to the vitamin part of self-treatment protocols.

Read the original source
Retracted case series; Tippens query returned 0 records

Case report

Makis W et al. Case Rep Oncol. 2025;18(1):856-863. PMID 40605964.

A 2025 case series of self-treating patients is marked RETRACTED ARTICLE in PubMed, with a retraction notice in Case Rep Oncol, 2026 Jan 21;19(1):169. It is not cited as support for any outcome. The remission story that sellers cite is a personal account, not a study: a PubMed query for Tippens AND fenbendazole run on 10 October 2026 returned 0 records.

Participants / model
Adults who self-treated, per a retracted report
Treatment
Not reproduced because the report is retracted
Follow-up
Not applicable
Study design
Retracted case series; a personal account that is not a study
Funding
not stated in the source

Retracted, so it cannot be cited as support. Self-reports with other treatments and no control cannot show that any drug caused a tumor response.

Read the original source

Studies and sources

PubChem: fenbendazole identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 3334, fenbendazole.

Fenbendazole is a benzimidazole carbamate anthelmintic, PubChem CID 3334, C15H13N3O2S, 299.3 g/mol, CAS 43210-67-9, IUPAC name methyl N-(6-phenylsulfanyl-1H-benzimidazol-2-yl)carbamate. Synonyms include Panacur, Safe-Guard and Hoe 881v. It is a single defined molecule with no salt form.

Participants / model
Chemical identity, not a clinical population
Treatment
Defined molecule
Follow-up
Not applicable
Study design
Chemical database record
Funding
not stated in the source

Identity record only. Material used for self-treatment is typically animal-grade product, and DailyMed lists many fenbendazole suspensions, pastes and tablets from different labelers whose excipients and purity are not those of any product studied in people. Oxfendazole is a different drug, related by metabolism.

Read the original source
Veterinary labels: dogs, cattle and goats; no human application found

Official label

DailyMed, National Library of Medicine. Panacur C Canine (fenbendazole) granules, Merck Animal Health, label effective 2026-05-15. Safe-Guard suspension 10% (set ID 9188886a-54bc-4c68-9f1d-37a20e031076), label effective 2026-06-17. openFDA Drugs@FDA query for fenbendazole, run 10 October 2026.

FDA approves fenbendazole as an animal drug. The Panacur C Canine label (Merck Animal Health, label effective 15 May 2026) is for dogs only, covers roundworms, hookworms, whipworms and tapeworms, and states approval under NADA 121-473. In US clinical studies 3 of 240 dogs (about 1%) vomited. The Safe-Guard suspension 10% label (set ID 9188886a-54bc-4c68-9f1d-37a20e031076, label effective 17 June 2026) is for beef and dairy cattle and goats under NADA 128-620 and carries withdrawal periods for meat and milk. An openFDA Drugs@FDA query for fenbendazole returned no match, so no human drug application was found. Approval status of the other labelers on DailyMed was not reviewed.

Participants / model
Dogs; cattle and goats
Treatment
Oral granules; oral suspension
Follow-up
Label versions effective 15 May 2026 and 17 June 2026
Study design
Veterinary labels plus a regulatory database query
Funding
not stated in the source

Veterinary labels only. They are not human prescribing information and give no basis for human use. Label dosing is not reproduced on this page.

Read the original source
LiverTox: not approved for humans; acute liver injury possible

Regulatory record

Hoofnagle JH. Fenbendazole. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2012. PMID 42081641.

The entry states that fenbendazole is used mainly for worm infestations in domestic cats and dogs, is not approved for use in humans, and has been claimed to have antineoplastic activity, and that because it is sold over the counter it has been used off label for cancer. It states that therapy is commonly associated with mild and transient serum enzyme elevations and can also lead to clinically apparent acute liver injury.

Participants / model
Humans, summary of the case literature
Treatment
Oral veterinary product
Follow-up
Not applicable
Study design
NIH drug-induced liver injury reference (LiverTox)
Funding
not stated in the source

Summary of the case literature. The record reviewed gives no incidence figure.

Read the original source
Case report: 67-year-old woman, jaundice, histologically confirmed injury

Case report

Thakurdesai A et al. ACG Case Rep J. 2024;11(5):e01354. PMID 38706451.

A 67-year-old woman with 2 weeks of jaundice after self-administering fenbendazole had histologically confirmed severe hepatocellular drug-induced liver injury, with liver tests normal 3 months after stopping.

Participants / model
A 67-year-old woman
Treatment
Self-administered veterinary fenbendazole
Follow-up
2 weeks of jaundice before presentation; liver tests normal 3 months after stopping
Study design
Single case report
Funding
not stated in the source

A single case with histologic confirmation. It shows what happened to one person, not how often this happens.

Read the original source
Case report: 65-year-old man, ALT 1764 U/L, RUCAM 9 for the pair

Case report

Powderly GE et al. Cureus. 2026;18(5):e108896. PMID 42299164.

A 65-year-old man with prostate cancer took veterinary fenbendazole and ivermectin for 3 months and presented with jaundice and abdominal pain: ALT 1764 U/L, AST 1132 U/L, total bilirubin 12.9 mg/dL and R-value 37.50, with viral, autoimmune and biliary causes ruled out. Transaminases fell 58% within 9 days and normalized within 6 weeks after both agents were stopped, and the RUCAM score was 9 (highly probable) for the pair.

Participants / model
A 65-year-old man with prostate cancer
Treatment
Self-administered veterinary fenbendazole and ivermectin
Follow-up
3 months of use; transaminases normalized within 6 weeks of stopping
Study design
Single case report
Funding
not stated in the source

Fenbendazole cannot be separated from ivermectin in this case, because the RUCAM score applies to the pair.

Read the original source
Case report: 80-year-old woman on pembrolizumab, spontaneous recovery

Case report

Yamaguchi T et al. Case Rep Oncol. 2021;14(2):886-891. PMID 34248555.

An 80-year-old woman with advanced non-small cell lung cancer on pembrolizumab had severe liver injury 9 months after starting it, after one month of fenbendazole taken on social media information. The dysfunction resolved spontaneously after she stopped, and she had no tumor shrinkage.

Participants / model
An 80-year-old woman with advanced non-small cell lung cancer on pembrolizumab
Treatment
Self-administered veterinary fenbendazole alongside pembrolizumab
Follow-up
One month of fenbendazole; injury 9 months after starting pembrolizumab
Study design
Single case report
Funding
not stated in the source

Attribution is hard because she was also on an immune checkpoint inhibitor.

Read the original source
Case report: 47-year-old woman on nivolumab and relatlimab, RUCAM 8

Case report

Krishnan A et al. World J Clin Cases. 2026;14(2):116700. PMID 41608149.

A 47-year-old woman with metastatic colon cancer on nivolumab and relatlimab had severe hepatocellular injury after raising her fenbendazole dose, with RUCAM 8 (probable), quick biochemical improvement after stopping and safe reintroduction of immunotherapy.

Participants / model
A 47-year-old woman with metastatic colon cancer on nivolumab and relatlimab
Treatment
Self-administered veterinary fenbendazole alongside immunotherapy
Follow-up
not stated in the source
Study design
Single case report
Funding
not stated in the source

Attribution is hard because she was also on immune checkpoint inhibitors.

Read the original source
Retracted case series; Tippens query returned 0 records

Case report

Makis W et al. Case Rep Oncol. 2025;18(1):856-863. PMID 40605964.

A 2025 case series of self-treating patients is marked RETRACTED ARTICLE in PubMed, with a retraction notice in Case Rep Oncol, 2026 Jan 21;19(1):169. It is not cited as support for any outcome. The remission story that sellers cite is a personal account, not a study: a PubMed query for Tippens AND fenbendazole run on 10 October 2026 returned 0 records.

Participants / model
Adults who self-treated, per a retracted report
Treatment
Not reproduced because the report is retracted
Follow-up
Not applicable
Study design
Retracted case series; a personal account that is not a study
Funding
not stated in the source

Retracted, so it cannot be cited as support. Self-reports with other treatments and no control cannot show that any drug caused a tumor response.

Read the original source
Cells and nu/nu mice: tubulin, p53, glucose uptake, xenograft growth

Animal study

Dogra N et al. Sci Rep. 2018;8(1):11926. PMID 30093705.

Fenbendazole showed moderate affinity for mammalian tubulin and was cytotoxic to human cancer cells at micromolar concentrations. It caused mitochondrial translocation of p53 and inhibited glucose uptake, GLUT transporter expression and hexokinase II. Fed orally to nu/nu mice, it blocked the growth of human xenografts. The abstract gives no dose, tumor type or effect size.

Participants / model
Human cancer cell lines; nu/nu mice with human xenografts
Treatment
Fenbendazole in cell culture; oral feeding in mice; dose not stated in the abstract
Follow-up
not stated in the source
Study design
Original preclinical study, cell culture and mouse xenografts
Funding
not stated in the source

Cells and mice only. The abstract gives no dose, tumor type or effect size, and the later mouse studies below did not all agree with it.

Read the original source
EMT6 cells toxic in vitro; no change in EMT6 tumor growth in mice

Animal study

Duan Q et al. Anticancer Res. 2013;33(2):355-62. PMID 23393324.

In EMT6 mouse mammary tumor cells, intensive fenbendazole was toxic in vitro (more so under severe hypoxia) and additive with radiation or docetaxel. Maximally intensive regimens did not alter EMT6 tumor growth in mice or add to radiation, and the authors report no evidence that it has value in cancer therapy.

Participants / model
EMT6 mouse mammary tumor cells; mice with EMT6 tumors
Treatment
Fenbendazole in cell culture and in mice, alone and with radiation or docetaxel; dose and route not stated in the source
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

A negative tumor-growth result in mice.

Read the original source
150 ppm fenbendazole diet: no change in EMT6 tumors in BALB/c mice

Animal study

Duan Q et al. J Am Assoc Lab Anim Sci. 2012;51(2):224-30. PMID 22776123.

A 150 ppm fenbendazole diet did not change EMT6 tumor growth, invasion or metastasis in BALB/c mice.

Participants / model
BALB/c mice with EMT6 mammary tumors
Treatment
Fenbendazole at 150 ppm in the diet
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

A negative result in mice. Dietary ppm in mice does not convert to a human dose.

Read the original source
20 SCID mice, 4 diet groups: effect only with fenbendazole plus vitamins

Animal study

Gao P et al. J Am Assoc Lab Anim Sci. 2008;47(6):37-40. PMID 19049251.

In SCID mice with a human lymphoma xenograft (20 mice, 4 diet groups), neither fenbendazole alone nor supplementary vitamins alone changed tumor growth, but the two together significantly inhibited it. The authors call the mechanism unknown, and the abstract does not name which vitamins.

Participants / model
20 SCID mice with a human lymphoma xenograft
Treatment
Four diet groups, including fenbendazole alone, supplementary vitamins alone and both together; doses not stated in the source
Follow-up
not stated in the source
Study design
Controlled preclinical study
Funding
not stated in the source

One small SCID study with no berberine or cannabidiol arm. It is the only experimental link in the records reviewed to the vitamin part of self-treatment protocols.

Read the original source
70 F344 rats, 8 weeks: liver hypertrophy, CYP induction, possible tumor promoter

Animal study

Shoda T et al. Toxicol Pathol. 1999;27(5):553-62. PMID 10528635.

In 70 male F344 rats given a single intraperitoneal injection of 100 mg/kg diethylnitrosamine (DEN) or vehicle and then fenbendazole in the diet at 3,600 to 70 ppm for 8 weeks, relative liver weight rose and periportal hepatocellular hypertrophy appeared at 600 ppm and above with or without DEN, and CYP1A2, 2B1 and 4A1 were induced. After DEN, connexin 32 fell and GST-P positive cells rose at 1,800 and 3,600 ppm, and the authors conclude that fenbendazole may be a liver tumor promoter.

Participants / model
70 male F344 rats
Treatment
A single intraperitoneal injection of 100 mg/kg diethylnitrosamine or vehicle, then fenbendazole in the diet at 3,600 to 70 ppm
Follow-up
8 weeks of dietary fenbendazole
Study design
Controlled toxicology study
Funding
not stated in the source

Rats only. Dietary ppm in rats does not convert to a human dose.

Read the original source
2007 review: not a carcinogen in lifetime rat studies, possible tumor promoter

Animal study

Villar D et al. J Am Assoc Lab Anim Sci. 2007;46(6):8-15. PMID 17994667.

A 2007 review of rodent studies states that lifetime rat studies show fenbendazole is not a carcinogen but may act as a tumor promoter after certain initiators.

Participants / model
Rodent literature
Treatment
not stated in the source
Follow-up
not stated in the source
Study design
Review of rodent studies
Funding
not stated in the source

A rodent review, not human data.

Read the original source
3 trial-type records, none about cancer; no registered fenbendazole study

PubMed search record

PubMed search for fenbendazole AND humans[mh] AND (randomized controlled trial[pt] OR clinical trial[pt] OR controlled clinical trial[pt]), run 10 October 2026. ClinicalTrials.gov query for fenbendazole and a PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin, both run the same day.

A PubMed search on 10 October 2026 for fenbendazole in humans with randomized controlled trial, clinical trial or controlled clinical trial publication types returned 3 records: two anthelmintic reports from 1976 and 1980 (PMIDs 779682 and 7010692) and a 2026 oxfendazole pharmacokinetic paper (PMID 41662151). None concerned cancer. The 1976 trial gave single doses per person against intestinal worms, reporting effectiveness against Ascaris, substantial egg count reductions for hookworm and good results against Trichuris at the higher dose, and its abstract reports no safety outcome. A ClinicalTrials.gov query for fenbendazole the same day returned 9 records: 5 oxfendazole studies and 4 unrelated studies, so no registered study of fenbendazole itself and no registered cancer trial. No human pharmacokinetics of fenbendazole given as itself were found; the closest is a healthy-adult oxfendazole study (PMID 33526484) that modeled fenbendazole as a metabolite. A 2024 review (PMID 39197912) states that fenbendazole is not approved by FDA or EMA and that its human pharmacokinetics and safety are not well documented. A PubMed query for fenbendazole with vitamin E succinate, berberine, cannabidiol or curcumin returned 1 record, a honey bee paper.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Searches run on 10 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 10 October 2026, not proof that no unpublished work exists. Oxfendazole is a separate drug and is not cited as fenbendazole evidence.

Read the original source

Why is Fenbendazole in F tier?

F fits a compound with documented human harm and no human efficacy data. Case reports describe severe liver injury after self-sourced use, LiverTox lists clinically apparent acute liver injury, and a rat study points to liver tumor promotion. Against that stand conflicting cell and mouse cancer results, no controlled human cancer study and a retracted case series.