Mibolerone

updated

Mibolerone is a 19-nor androgen sold as Cheque Drops, and its only approval in the US record is veterinary: an oral solution for preventing estrus in adult female dogs. No study of mibolerone in a person exists. The dog and cat work records clitoral enlargement, masculinized female offspring, thyroid changes in cats and ovarian fibromas in 12 of 92 dogs on long-term dosing, and no study in any species shows it increases aggression, focus or performance.

17-alpha-alkylated 19-nor androgen (anabolic androgenic steroid)

  • FDA's only codified approvals for mibolerone are veterinary: an oral solution for dogs only (21 CFR 520.1430) and a medicated-feed entry (21 CFR 558.348). It is a Schedule III controlled substance (21 CFR 1308.13(f)(63)).
  • Mibolerone is 7-alpha,17-alpha-dimethyl-19-nortestosterone, nandrolone with a 7-alpha and a 17-alpha methyl group (PubChem CID 251636, C20H30O2, molecular weight 302.5).
  • A 9.6-year dog study found small dense ovarian fibromas in 12 of 92 dogs given mibolerone at the approximate efficacious dose, and none in 60 vehicle controls or 55 animals on exaggerated doses.
  • Female offspring of treated Beagle bitches were masculinized, and cats developed cervical dermal thickening and clitoral hypertrophy after 3 months.
  • A PubMed search on 9 October 2026 returned 248 records for mibolerone; the only clinical-trial-type record is a dog field trial, and none involves a human clinical trial.
  • No study in any species shows mibolerone increases aggression, focus or performance; the one behavioral observation, in cats, recorded no behavioral change.

What is mibolerone, and who has approved it?

Mibolerone is 7-alpha,17-alpha-dimethyl-19-nortestosterone, nandrolone with two added methyl groups. Its only approval in the US record is veterinary, for preventing estrus in adult female dogs. It has no human product and is a Schedule III controlled substance.

Mibolerone is PubChem CID 251636, C20H30O2, molecular weight 302.5, CAS 3704-09-4. PubChem lists Cheque Drops, Cheque, Dihydrolone, Matenon and U-10,997 among its synonyms, and the systematic name 17-beta-hydroxy-7-alpha,17-dimethylestr-4-en-3-one. The estr-4-en-3-one skeleton is the 19-nor skeleton of nandrolone, so mibolerone is nandrolone with a 7-alpha methyl and a 17-alpha methyl. The chemical description sellers use is correct.

The only approval is veterinary. 21 CFR 520.1430 specifies an oral solution of mibolerone for use in dogs only, for the prevention of estrus (heat) in adult female dogs not intended primarily for breeding purposes. It sets a maximum duration of treatment, and federal law restricts the drug to use by or on the order of a licensed veterinarian. A second codified entry, 21 CFR 558.348, covers mibolerone in medicated animal feed. An openFDA Drugs@FDA substance-name query for mibolerone returned no matches on 9 October 2026, and DailyMed returned no human label, so no human product has ever existed in the US record.

Mibolerone is a Schedule III controlled substance in the United States. 21 CFR 1308.13(f)(63) lists it among anabolic steroids, DEA code 4000, covering salts, esters and ethers. The WADA 2026 Prohibited List, in effect 1 January 2026, names mibolerone under S1.1, anabolic androgenic steroids, prohibited at all times as a non-specified substance, and S0 separately prohibits substances approved only for veterinary use, which is mibolerone's status. Legal status outside the United States is not covered here.

PubChem: mibolerone identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 251636, mibolerone.

Mibolerone is PubChem CID 251636, C20H30O2, molecular weight 302.5, CAS 3704-09-4. Listed synonyms include Cheque Drops, Cheque, Dihydrolone, Matenon and U-10,997, and the systematic name is 17-beta-hydroxy-7-alpha,17-dimethylestr-4-en-3-one. The estr-4-en-3-one skeleton is the 19-nor skeleton of nandrolone, so mibolerone is 7-alpha,17-alpha-dimethyl-19-nortestosterone: nandrolone with a 7-alpha methyl and a 17-alpha methyl.

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

The chemical description sellers use (17-alpha-alkylated, 7-alpha-methylated, nandrolone-derived) matches this record. Identity record only; it says nothing about activity or safety in people.

Read the original source
US veterinary regulation: dogs only, estrus prevention

Regulatory record

Electronic Code of Federal Regulations, Title 21, section 520.1430, mibolerone. Rule history: 43 FR 15625, 14 April 1978, as amended at 78 FR 28824, 20 May 2014.

The regulation specifies an oral solution of mibolerone for use in dogs only, for the prevention of estrus (heat) in adult female dogs not intended primarily for breeding purposes. It sets a maximum duration of treatment and restricts the drug to use by or on the order of a licensed veterinarian. A second codified entry, 21 CFR 558.348, covers mibolerone in medicated animal feed.

Participants / model
Adult female dogs
Treatment
Oral solution, for dogs only
Follow-up
Rule in force; history 1978 to 2014 amendment
Study design
Codified federal regulation
Funding
not stated in the source

The only approval mibolerone has in the US record is veterinary. This page does not reproduce label dosing.

Read the original source
No human drug application found

Regulatory record

openFDA Drugs@FDA API, substance_name MIBOLERONE, queried 9 October 2026. DailyMed search run the same day.

An openFDA Drugs@FDA substance-name query for MIBOLERONE returned no matches on 9 October 2026, and a DailyMed search returned no human label. The only codified US approvals are the two veterinary entries in 21 CFR 520.1430 and 21 CFR 558.348.

Participants / model
Regulatory records, not a population
Treatment
Not applicable
Follow-up
Query run on 9 October 2026
Study design
Official FDA API query
Funding
not stated in the source

Shows the absence of any human marketing authorization in the US record.

Read the original source
Schedule III and WADA S1.1

Regulatory record

Electronic Code of Federal Regulations, Title 21, section 1308.13, Schedule III. World Anti-Doping Agency, The 2026 Prohibited List, in effect 1 January 2026.

21 CFR 1308.13(f)(63) lists mibolerone (7alpha,17alpha-dimethyl-17beta-hydroxyestr-4-en-3-one) among anabolic steroids in Schedule III, DEA code 4000, covering salts, esters and ethers. The WADA 2026 Prohibited List names mibolerone under S1.1, anabolic androgenic steroids, prohibited at all times as a non-specified substance. S0 separately prohibits substances approved only for veterinary use, which is mibolerone's status.

Participants / model
Regulatory and anti-doping records, not a population
Treatment
Not applicable
Follow-up
Current eCFR; WADA list in effect 1 January 2026
Study design
Codified federal regulation and official anti-doping record
Funding
not stated in the source

Legal status outside the United States is not covered.

Read the original source

What did the dog and cat studies find?

In Beagle bitches and domestic cats mibolerone prevented estrus, and it also caused clitoral enlargement, masculinized female dog offspring and, in cats, thyroid changes. A 9.6-year dog study found ovarian fibromas in 12 of 92 dogs given the approximate efficacious dose.

The pivotal dog data come from female Beagles. Oral mibolerone inhibited estrous activity in immature and mature bitches in studies lasting up to 730 days. The lowest daily dose tested was 70% effective at preventing estrus. Observed effects included estrus inhibition, prolongation of the interestrous interval at that lowest dose, vaginal discharge, and a dose-related increase in clitoral size. Post-treatment conception rate fell only in bitches receiving the lowest dose for 730 days.

In pregnant Beagles, mibolerone given from 1, 3 or 6 days after first breeding until weaning produced no adverse effects on conception, pregnancy or parturition in the treated bitches, but female offspring were masculinized. There were no gross effects on male offspring.

A 9.6-year study of prolonged oral mibolerone in female dogs found small dense ovarian tumors in 12 of 92 dogs given mibolerone at the approximate efficacious dose. No such tumors appeared in 60 vehicle controls or in 55 animals given exaggerated doses. The tumors were fibromas, growing by expansion with no invasion or metastasis.

In a 280-day study in domestic cats, the highest daily regimen prevented estrus over 180 days, while the lower daily regimen and a weekly regimen did not. Systemic metabolic changes were detected only in thyroid function, as dose- and time-related changes in serum cholesterol, thyroid gland weight and thyroid histology, without clinical thyroid dysfunction over 6 months. Masculinizing changes, cervical dermal thickening and clitoral hypertrophy, were apparent after 3 months on either daily regimen. The authors state that behavioral changes were not observed.

Veterinary study doses are not reproduced on this page. They were chosen for dogs and cats and are not human doses.

Beagles: estrus inhibition for up to 730 days

Animal study

Sokolowski JH et al. Am J Vet Res. 1977;38(9):1371-6. PMID 921032.

Mibolerone inhibited estrous activity in immature and mature Beagle bitches given oral doses for up to 730 days. The lowest daily dose tested was 70% effective at preventing estrus. Observed effects included estrus inhibition, prolongation of the interestrous interval at that lowest dose, vaginal discharge, and a dose-related increase in clitoral size. Post-treatment conception rate fell only in bitches receiving the lowest dose for 730 days.

Participants / model
Immature and mature female Beagles
Treatment
Oral mibolerone, daily, up to 730 days; doses not reproduced on this page
Follow-up
Up to 730 days
Study design
Controlled veterinary pharmacology and tolerance study
Funding
not stated in the source

The pivotal dog efficacy and tolerance data. Veterinary doses are not reproduced and are not human doses.

Read the original source
Pregnant Beagles: female offspring masculinized

Animal study

Sokolowski JH et al. Am J Vet Res. 1978;39(5):837-9. PMID 727584.

Mibolerone given to Beagle bitches from 1, 3 or 6 days after first breeding until weaning produced no adverse effects on conception, pregnancy or parturition in the treated bitches, but female offspring were masculinized. There were no gross effects on male offspring.

Participants / model
Pregnant Beagles and their offspring
Treatment
Oral mibolerone, daily, from after first breeding until weaning; doses not reproduced on this page
Follow-up
From 1, 3 or 6 days after first breeding until weaning
Study design
Controlled veterinary reproductive toxicity study
Funding
not stated in the source

Veterinary study in dogs. It says nothing about pregnancy in people.

Read the original source
9.6-year dog study: ovarian fibromas in 12 of 92

Animal study

Seaman WJ. Toxicol Pathol. 1985;13(3):177-80. PMID 4070927.

A 9.6-year study of prolonged oral mibolerone in female dogs found small dense ovarian tumors in 12 of 92 dogs given mibolerone at the approximate efficacious dose. No such tumors appeared in 60 vehicle controls or in 55 animals given exaggerated doses. The tumors were fibromas, growing by expansion with no invasion or metastasis.

Participants / model
Female dogs: 92 treated at the approximate efficacious dose, 60 vehicle controls and 55 on exaggerated doses
Treatment
Prolonged oral mibolerone; doses not reproduced on this page
Follow-up
9.6 years
Study design
Long-term preclinical toxicology study
Funding
not stated in the source

Veterinary toxicology in dogs. The tumors were fibromas that grew by expansion without invasion or metastasis.

Read the original source
Domestic cats, 280 days: thyroid and masculinizing changes

Animal study

Burke TJ et al. Am J Vet Res. 1977;38(4):469-77. PMID 851279.

In domestic cats, the highest daily regimen prevented estrus over 180 days; the lower daily regimen and a weekly regimen did not. Systemic metabolic changes were detected only in thyroid function, as dose- and time-related changes in serum cholesterol, thyroid gland weight and thyroid histology, without clinical thyroid dysfunction over 6 months. Masculinizing changes, cervical dermal thickening and clitoral hypertrophy, were apparent after 3 months on either daily regimen. The authors state that behavioral changes were not observed.

Participants / model
Domestic cats, 280-day study
Treatment
Oral mibolerone, two daily regimens and one weekly regimen; doses not reproduced on this page
Follow-up
280 days; estrus assessed over 180 days
Study design
Controlled veterinary study
Funding
not stated in the source

The one behavioral observation in the mibolerone literature, and it is a null result.

Read the original source

Has mibolerone ever been studied in people?

No. A PubMed search on 9 October 2026 returned 248 records. Only 1 was a clinical-trial-type record, a dog field trial, and restricting to humans with clinical trial or randomized controlled trial types returned 0.

The one clinical-trial-type record is a controlled blind-labeled field trial of mibolerone for pseudopregnancy in 63 bitches plus 17 placebo controls. The large human-indexed literature is laboratory work, where tritiated mibolerone is used as a radioligand to measure androgen receptor binding in human tissue and cell lines. Mibolerone has never been studied in a person.

No human product exists in the US record. The only codified US approvals are the two veterinary entries described above.

PubMed: 248 records, no human study

PubMed search record

PubMed search for mibolerone, run 9 October 2026, then restricted to the clinical trial publication type.

A PubMed search for mibolerone returned 248 records. Restricting to the clinical trial publication type returned exactly 1 record, a controlled blind-labeled field trial of mibolerone for pseudopregnancy in 63 bitches plus 17 placebo controls. Restricting to humans with clinical trial or randomized controlled trial publication types returned 0 records. The large human-indexed literature on mibolerone is laboratory work, where tritiated mibolerone is used as a radioligand to measure androgen receptor binding in human tissue and cell lines.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature search
Funding
not stated in the source

An absence finding as of 9 October 2026. Mibolerone has not been studied in a person in these records.

Read the original source
No human drug application found

Regulatory record

openFDA Drugs@FDA API, substance_name MIBOLERONE, queried 9 October 2026. DailyMed search run the same day.

An openFDA Drugs@FDA substance-name query for MIBOLERONE returned no matches on 9 October 2026, and a DailyMed search returned no human label. The only codified US approvals are the two veterinary entries in 21 CFR 520.1430 and 21 CFR 558.348.

Participants / model
Regulatory records, not a population
Treatment
Not applicable
Follow-up
Query run on 9 October 2026
Study design
Official FDA API query
Funding
not stated in the source

Shows the absence of any human marketing authorization in the US record.

Read the original source

Does mibolerone increase aggression, focus or performance?

No evidence in any species supports it. A PubMed search on 9 October 2026 for mibolerone with aggression returned 2 records, neither reporting an aggression outcome, and the one behavioral observation in the literature, in cats, recorded no behavioral change.

Sellers describe mibolerone as an extremely potent, short-acting androgen used for pre-event aggression and focus rather than muscle, and as 17-alpha-alkylated, 7-alpha-methylated and nandrolone-derived. The chemistry is right, confirmed by the PubChem record and the DEA listing. The pharmacology claim has no record behind it.

The 2 aggression records are a greyhound urinary metabolite study and a single-dog veterinary behavior case report about aggression after ovariohysterectomy, with no abstract indexed. A search for mibolerone with strength, performance, muscle mass, athlete or doping returned 19 records, which are receptor-biology papers plus the greyhound metabolite study. The cat study recorded no behavioral change.

Extremely potent fits the very small amounts used in the veterinary label, but no human potency comparison has been published. Short-acting could not be sourced, because no human or canine half-life was located.

PubMed: 2 records on aggression, neither an outcome

PubMed search record

PubMed search for mibolerone combined with aggression or aggressive, run 9 October 2026. A second search combined mibolerone with strength, performance, muscle mass, athlete or doping.

A PubMed search for mibolerone with aggression or aggressive returned 2 records. Neither reports an aggression outcome from mibolerone in any species: one is the greyhound urinary metabolite study and the other is a single-dog veterinary behavior case report about aggression after ovariohysterectomy, with no abstract indexed. A search for mibolerone with strength, performance, muscle mass, athlete or doping returned 19 records, which are receptor-biology papers plus the greyhound metabolite study. The one behavioral observation in the entire mibolerone literature is the cat study, which recorded no behavioral change.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature search
Funding
not stated in the source

No evidence that mibolerone increases aggression, focus or performance in any species, and none at all in people.

Read the original source
Domestic cats, 280 days: thyroid and masculinizing changes

Animal study

Burke TJ et al. Am J Vet Res. 1977;38(4):469-77. PMID 851279.

In domestic cats, the highest daily regimen prevented estrus over 180 days; the lower daily regimen and a weekly regimen did not. Systemic metabolic changes were detected only in thyroid function, as dose- and time-related changes in serum cholesterol, thyroid gland weight and thyroid histology, without clinical thyroid dysfunction over 6 months. Masculinizing changes, cervical dermal thickening and clitoral hypertrophy, were apparent after 3 months on either daily regimen. The authors state that behavioral changes were not observed.

Participants / model
Domestic cats, 280-day study
Treatment
Oral mibolerone, two daily regimens and one weekly regimen; doses not reproduced on this page
Follow-up
280 days; estrus assessed over 180 days
Study design
Controlled veterinary study
Funding
not stated in the source

The one behavioral observation in the mibolerone literature, and it is a null result.

Read the original source
PubChem: mibolerone identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 251636, mibolerone.

Mibolerone is PubChem CID 251636, C20H30O2, molecular weight 302.5, CAS 3704-09-4. Listed synonyms include Cheque Drops, Cheque, Dihydrolone, Matenon and U-10,997, and the systematic name is 17-beta-hydroxy-7-alpha,17-dimethylestr-4-en-3-one. The estr-4-en-3-one skeleton is the 19-nor skeleton of nandrolone, so mibolerone is 7-alpha,17-alpha-dimethyl-19-nortestosterone: nandrolone with a 7-alpha methyl and a 17-alpha methyl.

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

The chemical description sellers use (17-alpha-alkylated, 7-alpha-methylated, nandrolone-derived) matches this record. Identity record only; it says nothing about activity or safety in people.

Read the original source

How does mibolerone act, and how long does it last?

Mibolerone is an androgen, and in the laboratory tritiated mibolerone is used as a radioligand to measure androgen receptor binding. No half-life or other pharmacokinetic figure was located, so the short-acting description is not established.

Mibolerone is a 19-nor androgen, nandrolone with a 7-alpha and a 17-alpha methyl group. Tritiated mibolerone is used in the laboratory as a radioligand to measure androgen receptor binding in human tissue and cell lines. In dogs and cats it prevented estrus and caused masculinizing changes.

No human or canine half-life, bioavailability or other pharmacokinetic figure was located in the sources reviewed.

PubChem: mibolerone identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 251636, mibolerone.

Mibolerone is PubChem CID 251636, C20H30O2, molecular weight 302.5, CAS 3704-09-4. Listed synonyms include Cheque Drops, Cheque, Dihydrolone, Matenon and U-10,997, and the systematic name is 17-beta-hydroxy-7-alpha,17-dimethylestr-4-en-3-one. The estr-4-en-3-one skeleton is the 19-nor skeleton of nandrolone, so mibolerone is 7-alpha,17-alpha-dimethyl-19-nortestosterone: nandrolone with a 7-alpha methyl and a 17-alpha methyl.

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

The chemical description sellers use (17-alpha-alkylated, 7-alpha-methylated, nandrolone-derived) matches this record. Identity record only; it says nothing about activity or safety in people.

Read the original source
PubMed: 248 records, no human study

PubMed search record

PubMed search for mibolerone, run 9 October 2026, then restricted to the clinical trial publication type.

A PubMed search for mibolerone returned 248 records. Restricting to the clinical trial publication type returned exactly 1 record, a controlled blind-labeled field trial of mibolerone for pseudopregnancy in 63 bitches plus 17 placebo controls. Restricting to humans with clinical trial or randomized controlled trial publication types returned 0 records. The large human-indexed literature on mibolerone is laboratory work, where tritiated mibolerone is used as a radioligand to measure androgen receptor binding in human tissue and cell lines.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature search
Funding
not stated in the source

An absence finding as of 9 October 2026. Mibolerone has not been studied in a person in these records.

Read the original source
Beagles: estrus inhibition for up to 730 days

Animal study

Sokolowski JH et al. Am J Vet Res. 1977;38(9):1371-6. PMID 921032.

Mibolerone inhibited estrous activity in immature and mature Beagle bitches given oral doses for up to 730 days. The lowest daily dose tested was 70% effective at preventing estrus. Observed effects included estrus inhibition, prolongation of the interestrous interval at that lowest dose, vaginal discharge, and a dose-related increase in clitoral size. Post-treatment conception rate fell only in bitches receiving the lowest dose for 730 days.

Participants / model
Immature and mature female Beagles
Treatment
Oral mibolerone, daily, up to 730 days; doses not reproduced on this page
Follow-up
Up to 730 days
Study design
Controlled veterinary pharmacology and tolerance study
Funding
not stated in the source

The pivotal dog efficacy and tolerance data. Veterinary doses are not reproduced and are not human doses.

Read the original source
Domestic cats, 280 days: thyroid and masculinizing changes

Animal study

Burke TJ et al. Am J Vet Res. 1977;38(4):469-77. PMID 851279.

In domestic cats, the highest daily regimen prevented estrus over 180 days; the lower daily regimen and a weekly regimen did not. Systemic metabolic changes were detected only in thyroid function, as dose- and time-related changes in serum cholesterol, thyroid gland weight and thyroid histology, without clinical thyroid dysfunction over 6 months. Masculinizing changes, cervical dermal thickening and clitoral hypertrophy, were apparent after 3 months on either daily regimen. The authors state that behavioral changes were not observed.

Participants / model
Domestic cats, 280-day study
Treatment
Oral mibolerone, two daily regimens and one weekly regimen; doses not reproduced on this page
Follow-up
280 days; estrus assessed over 180 days
Study design
Controlled veterinary study
Funding
not stated in the source

The one behavioral observation in the mibolerone literature, and it is a null result.

Read the original source

What is known about the safety of mibolerone?

No human safety data exist. In animals the record shows clitoral enlargement in dogs and cats, masculinized female offspring, thyroid changes in cats and ovarian fibromas in 12 of 92 dogs on long-term dosing. A liver risk is an inference from its chemistry, not a measured finding.

The animal findings are specific. Dogs showed a dose-related increase in clitoral size and, in one arm, a fall in post-treatment conception rate. Female offspring of treated Beagle bitches were masculinized. Cats developed cervical dermal thickening and clitoral hypertrophy after 3 months and changes in serum cholesterol, thyroid gland weight and thyroid histology, without clinical thyroid dysfunction over 6 months. In the 9.6-year dog study, small dense ovarian fibromas appeared in 12 of 92 dogs given mibolerone at the approximate efficacious dose.

Mibolerone is 17-alpha-alkylated, so it carries the liver liability of that class of steroids. This is an inference from its confirmed chemistry, not a measured finding for mibolerone, and no liver outcome for mibolerone appears in the sources reviewed.

No human outcome of any kind exists, because mibolerone has never been studied in a person. It is a Schedule III controlled substance in the United States, and its veterinary approval restricts it to use by or on the order of a licensed veterinarian.

Beagles: estrus inhibition for up to 730 days

Animal study

Sokolowski JH et al. Am J Vet Res. 1977;38(9):1371-6. PMID 921032.

Mibolerone inhibited estrous activity in immature and mature Beagle bitches given oral doses for up to 730 days. The lowest daily dose tested was 70% effective at preventing estrus. Observed effects included estrus inhibition, prolongation of the interestrous interval at that lowest dose, vaginal discharge, and a dose-related increase in clitoral size. Post-treatment conception rate fell only in bitches receiving the lowest dose for 730 days.

Participants / model
Immature and mature female Beagles
Treatment
Oral mibolerone, daily, up to 730 days; doses not reproduced on this page
Follow-up
Up to 730 days
Study design
Controlled veterinary pharmacology and tolerance study
Funding
not stated in the source

The pivotal dog efficacy and tolerance data. Veterinary doses are not reproduced and are not human doses.

Read the original source
Pregnant Beagles: female offspring masculinized

Animal study

Sokolowski JH et al. Am J Vet Res. 1978;39(5):837-9. PMID 727584.

Mibolerone given to Beagle bitches from 1, 3 or 6 days after first breeding until weaning produced no adverse effects on conception, pregnancy or parturition in the treated bitches, but female offspring were masculinized. There were no gross effects on male offspring.

Participants / model
Pregnant Beagles and their offspring
Treatment
Oral mibolerone, daily, from after first breeding until weaning; doses not reproduced on this page
Follow-up
From 1, 3 or 6 days after first breeding until weaning
Study design
Controlled veterinary reproductive toxicity study
Funding
not stated in the source

Veterinary study in dogs. It says nothing about pregnancy in people.

Read the original source
9.6-year dog study: ovarian fibromas in 12 of 92

Animal study

Seaman WJ. Toxicol Pathol. 1985;13(3):177-80. PMID 4070927.

A 9.6-year study of prolonged oral mibolerone in female dogs found small dense ovarian tumors in 12 of 92 dogs given mibolerone at the approximate efficacious dose. No such tumors appeared in 60 vehicle controls or in 55 animals given exaggerated doses. The tumors were fibromas, growing by expansion with no invasion or metastasis.

Participants / model
Female dogs: 92 treated at the approximate efficacious dose, 60 vehicle controls and 55 on exaggerated doses
Treatment
Prolonged oral mibolerone; doses not reproduced on this page
Follow-up
9.6 years
Study design
Long-term preclinical toxicology study
Funding
not stated in the source

Veterinary toxicology in dogs. The tumors were fibromas that grew by expansion without invasion or metastasis.

Read the original source
Domestic cats, 280 days: thyroid and masculinizing changes

Animal study

Burke TJ et al. Am J Vet Res. 1977;38(4):469-77. PMID 851279.

In domestic cats, the highest daily regimen prevented estrus over 180 days; the lower daily regimen and a weekly regimen did not. Systemic metabolic changes were detected only in thyroid function, as dose- and time-related changes in serum cholesterol, thyroid gland weight and thyroid histology, without clinical thyroid dysfunction over 6 months. Masculinizing changes, cervical dermal thickening and clitoral hypertrophy, were apparent after 3 months on either daily regimen. The authors state that behavioral changes were not observed.

Participants / model
Domestic cats, 280-day study
Treatment
Oral mibolerone, two daily regimens and one weekly regimen; doses not reproduced on this page
Follow-up
280 days; estrus assessed over 180 days
Study design
Controlled veterinary study
Funding
not stated in the source

The one behavioral observation in the mibolerone literature, and it is a null result.

Read the original source
PubChem: mibolerone identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 251636, mibolerone.

Mibolerone is PubChem CID 251636, C20H30O2, molecular weight 302.5, CAS 3704-09-4. Listed synonyms include Cheque Drops, Cheque, Dihydrolone, Matenon and U-10,997, and the systematic name is 17-beta-hydroxy-7-alpha,17-dimethylestr-4-en-3-one. The estr-4-en-3-one skeleton is the 19-nor skeleton of nandrolone, so mibolerone is 7-alpha,17-alpha-dimethyl-19-nortestosterone: nandrolone with a 7-alpha methyl and a 17-alpha methyl.

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

The chemical description sellers use (17-alpha-alkylated, 7-alpha-methylated, nandrolone-derived) matches this record. Identity record only; it says nothing about activity or safety in people.

Read the original source
Schedule III and WADA S1.1

Regulatory record

Electronic Code of Federal Regulations, Title 21, section 1308.13, Schedule III. World Anti-Doping Agency, The 2026 Prohibited List, in effect 1 January 2026.

21 CFR 1308.13(f)(63) lists mibolerone (7alpha,17alpha-dimethyl-17beta-hydroxyestr-4-en-3-one) among anabolic steroids in Schedule III, DEA code 4000, covering salts, esters and ethers. The WADA 2026 Prohibited List names mibolerone under S1.1, anabolic androgenic steroids, prohibited at all times as a non-specified substance. S0 separately prohibits substances approved only for veterinary use, which is mibolerone's status.

Participants / model
Regulatory and anti-doping records, not a population
Treatment
Not applicable
Follow-up
Current eCFR; WADA list in effect 1 January 2026
Study design
Codified federal regulation and official anti-doping record
Funding
not stated in the source

Legal status outside the United States is not covered.

Read the original source

Why does mibolerone sit in F tier?

The published downside outweighs any reported upside. The record is a veterinary estrus suppressant with documented masculinizing, thyroid and ovarian tumor findings and no human study, while the claimed aggression and focus benefit has no support in any species.

What the evidence base documents is clitoral enlargement in dogs and cats, masculinization of female offspring, thyroid changes in cats and ovarian fibromas in 12 of 92 dogs on long-term dosing. Against that, the claimed benefit has no evidence in any species: the single behavioral observation in the literature is a null result in cats, and the aggression and focus claims that drive its sale have never been tested.

It is a Schedule III androgen with no human study of any kind and a veterinary approval it was never meant to leave. The 17-alpha-alkyl liver liability is an inference from its chemistry, stated as such.

Beagles: estrus inhibition for up to 730 days

Animal study

Sokolowski JH et al. Am J Vet Res. 1977;38(9):1371-6. PMID 921032.

Mibolerone inhibited estrous activity in immature and mature Beagle bitches given oral doses for up to 730 days. The lowest daily dose tested was 70% effective at preventing estrus. Observed effects included estrus inhibition, prolongation of the interestrous interval at that lowest dose, vaginal discharge, and a dose-related increase in clitoral size. Post-treatment conception rate fell only in bitches receiving the lowest dose for 730 days.

Participants / model
Immature and mature female Beagles
Treatment
Oral mibolerone, daily, up to 730 days; doses not reproduced on this page
Follow-up
Up to 730 days
Study design
Controlled veterinary pharmacology and tolerance study
Funding
not stated in the source

The pivotal dog efficacy and tolerance data. Veterinary doses are not reproduced and are not human doses.

Read the original source
Pregnant Beagles: female offspring masculinized

Animal study

Sokolowski JH et al. Am J Vet Res. 1978;39(5):837-9. PMID 727584.

Mibolerone given to Beagle bitches from 1, 3 or 6 days after first breeding until weaning produced no adverse effects on conception, pregnancy or parturition in the treated bitches, but female offspring were masculinized. There were no gross effects on male offspring.

Participants / model
Pregnant Beagles and their offspring
Treatment
Oral mibolerone, daily, from after first breeding until weaning; doses not reproduced on this page
Follow-up
From 1, 3 or 6 days after first breeding until weaning
Study design
Controlled veterinary reproductive toxicity study
Funding
not stated in the source

Veterinary study in dogs. It says nothing about pregnancy in people.

Read the original source
9.6-year dog study: ovarian fibromas in 12 of 92

Animal study

Seaman WJ. Toxicol Pathol. 1985;13(3):177-80. PMID 4070927.

A 9.6-year study of prolonged oral mibolerone in female dogs found small dense ovarian tumors in 12 of 92 dogs given mibolerone at the approximate efficacious dose. No such tumors appeared in 60 vehicle controls or in 55 animals given exaggerated doses. The tumors were fibromas, growing by expansion with no invasion or metastasis.

Participants / model
Female dogs: 92 treated at the approximate efficacious dose, 60 vehicle controls and 55 on exaggerated doses
Treatment
Prolonged oral mibolerone; doses not reproduced on this page
Follow-up
9.6 years
Study design
Long-term preclinical toxicology study
Funding
not stated in the source

Veterinary toxicology in dogs. The tumors were fibromas that grew by expansion without invasion or metastasis.

Read the original source
Domestic cats, 280 days: thyroid and masculinizing changes

Animal study

Burke TJ et al. Am J Vet Res. 1977;38(4):469-77. PMID 851279.

In domestic cats, the highest daily regimen prevented estrus over 180 days; the lower daily regimen and a weekly regimen did not. Systemic metabolic changes were detected only in thyroid function, as dose- and time-related changes in serum cholesterol, thyroid gland weight and thyroid histology, without clinical thyroid dysfunction over 6 months. Masculinizing changes, cervical dermal thickening and clitoral hypertrophy, were apparent after 3 months on either daily regimen. The authors state that behavioral changes were not observed.

Participants / model
Domestic cats, 280-day study
Treatment
Oral mibolerone, two daily regimens and one weekly regimen; doses not reproduced on this page
Follow-up
280 days; estrus assessed over 180 days
Study design
Controlled veterinary study
Funding
not stated in the source

The one behavioral observation in the mibolerone literature, and it is a null result.

Read the original source
PubMed: 248 records, no human study

PubMed search record

PubMed search for mibolerone, run 9 October 2026, then restricted to the clinical trial publication type.

A PubMed search for mibolerone returned 248 records. Restricting to the clinical trial publication type returned exactly 1 record, a controlled blind-labeled field trial of mibolerone for pseudopregnancy in 63 bitches plus 17 placebo controls. Restricting to humans with clinical trial or randomized controlled trial publication types returned 0 records. The large human-indexed literature on mibolerone is laboratory work, where tritiated mibolerone is used as a radioligand to measure androgen receptor binding in human tissue and cell lines.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature search
Funding
not stated in the source

An absence finding as of 9 October 2026. Mibolerone has not been studied in a person in these records.

Read the original source
PubMed: 2 records on aggression, neither an outcome

PubMed search record

PubMed search for mibolerone combined with aggression or aggressive, run 9 October 2026. A second search combined mibolerone with strength, performance, muscle mass, athlete or doping.

A PubMed search for mibolerone with aggression or aggressive returned 2 records. Neither reports an aggression outcome from mibolerone in any species: one is the greyhound urinary metabolite study and the other is a single-dog veterinary behavior case report about aggression after ovariohysterectomy, with no abstract indexed. A search for mibolerone with strength, performance, muscle mass, athlete or doping returned 19 records, which are receptor-biology papers plus the greyhound metabolite study. The one behavioral observation in the entire mibolerone literature is the cat study, which recorded no behavioral change.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature search
Funding
not stated in the source

No evidence that mibolerone increases aggression, focus or performance in any species, and none at all in people.

Read the original source
Schedule III and WADA S1.1

Regulatory record

Electronic Code of Federal Regulations, Title 21, section 1308.13, Schedule III. World Anti-Doping Agency, The 2026 Prohibited List, in effect 1 January 2026.

21 CFR 1308.13(f)(63) lists mibolerone (7alpha,17alpha-dimethyl-17beta-hydroxyestr-4-en-3-one) among anabolic steroids in Schedule III, DEA code 4000, covering salts, esters and ethers. The WADA 2026 Prohibited List names mibolerone under S1.1, anabolic androgenic steroids, prohibited at all times as a non-specified substance. S0 separately prohibits substances approved only for veterinary use, which is mibolerone's status.

Participants / model
Regulatory and anti-doping records, not a population
Treatment
Not applicable
Follow-up
Current eCFR; WADA list in effect 1 January 2026
Study design
Codified federal regulation and official anti-doping record
Funding
not stated in the source

Legal status outside the United States is not covered.

Read the original source

Studies and sources

PubChem: mibolerone identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 251636, mibolerone.

Mibolerone is PubChem CID 251636, C20H30O2, molecular weight 302.5, CAS 3704-09-4. Listed synonyms include Cheque Drops, Cheque, Dihydrolone, Matenon and U-10,997, and the systematic name is 17-beta-hydroxy-7-alpha,17-dimethylestr-4-en-3-one. The estr-4-en-3-one skeleton is the 19-nor skeleton of nandrolone, so mibolerone is 7-alpha,17-alpha-dimethyl-19-nortestosterone: nandrolone with a 7-alpha methyl and a 17-alpha methyl.

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

The chemical description sellers use (17-alpha-alkylated, 7-alpha-methylated, nandrolone-derived) matches this record. Identity record only; it says nothing about activity or safety in people.

Read the original source
US veterinary regulation: dogs only, estrus prevention

Regulatory record

Electronic Code of Federal Regulations, Title 21, section 520.1430, mibolerone. Rule history: 43 FR 15625, 14 April 1978, as amended at 78 FR 28824, 20 May 2014.

The regulation specifies an oral solution of mibolerone for use in dogs only, for the prevention of estrus (heat) in adult female dogs not intended primarily for breeding purposes. It sets a maximum duration of treatment and restricts the drug to use by or on the order of a licensed veterinarian. A second codified entry, 21 CFR 558.348, covers mibolerone in medicated animal feed.

Participants / model
Adult female dogs
Treatment
Oral solution, for dogs only
Follow-up
Rule in force; history 1978 to 2014 amendment
Study design
Codified federal regulation
Funding
not stated in the source

The only approval mibolerone has in the US record is veterinary. This page does not reproduce label dosing.

Read the original source
Beagles: estrus inhibition for up to 730 days

Animal study

Sokolowski JH et al. Am J Vet Res. 1977;38(9):1371-6. PMID 921032.

Mibolerone inhibited estrous activity in immature and mature Beagle bitches given oral doses for up to 730 days. The lowest daily dose tested was 70% effective at preventing estrus. Observed effects included estrus inhibition, prolongation of the interestrous interval at that lowest dose, vaginal discharge, and a dose-related increase in clitoral size. Post-treatment conception rate fell only in bitches receiving the lowest dose for 730 days.

Participants / model
Immature and mature female Beagles
Treatment
Oral mibolerone, daily, up to 730 days; doses not reproduced on this page
Follow-up
Up to 730 days
Study design
Controlled veterinary pharmacology and tolerance study
Funding
not stated in the source

The pivotal dog efficacy and tolerance data. Veterinary doses are not reproduced and are not human doses.

Read the original source
Pregnant Beagles: female offspring masculinized

Animal study

Sokolowski JH et al. Am J Vet Res. 1978;39(5):837-9. PMID 727584.

Mibolerone given to Beagle bitches from 1, 3 or 6 days after first breeding until weaning produced no adverse effects on conception, pregnancy or parturition in the treated bitches, but female offspring were masculinized. There were no gross effects on male offspring.

Participants / model
Pregnant Beagles and their offspring
Treatment
Oral mibolerone, daily, from after first breeding until weaning; doses not reproduced on this page
Follow-up
From 1, 3 or 6 days after first breeding until weaning
Study design
Controlled veterinary reproductive toxicity study
Funding
not stated in the source

Veterinary study in dogs. It says nothing about pregnancy in people.

Read the original source
9.6-year dog study: ovarian fibromas in 12 of 92

Animal study

Seaman WJ. Toxicol Pathol. 1985;13(3):177-80. PMID 4070927.

A 9.6-year study of prolonged oral mibolerone in female dogs found small dense ovarian tumors in 12 of 92 dogs given mibolerone at the approximate efficacious dose. No such tumors appeared in 60 vehicle controls or in 55 animals given exaggerated doses. The tumors were fibromas, growing by expansion with no invasion or metastasis.

Participants / model
Female dogs: 92 treated at the approximate efficacious dose, 60 vehicle controls and 55 on exaggerated doses
Treatment
Prolonged oral mibolerone; doses not reproduced on this page
Follow-up
9.6 years
Study design
Long-term preclinical toxicology study
Funding
not stated in the source

Veterinary toxicology in dogs. The tumors were fibromas that grew by expansion without invasion or metastasis.

Read the original source
Domestic cats, 280 days: thyroid and masculinizing changes

Animal study

Burke TJ et al. Am J Vet Res. 1977;38(4):469-77. PMID 851279.

In domestic cats, the highest daily regimen prevented estrus over 180 days; the lower daily regimen and a weekly regimen did not. Systemic metabolic changes were detected only in thyroid function, as dose- and time-related changes in serum cholesterol, thyroid gland weight and thyroid histology, without clinical thyroid dysfunction over 6 months. Masculinizing changes, cervical dermal thickening and clitoral hypertrophy, were apparent after 3 months on either daily regimen. The authors state that behavioral changes were not observed.

Participants / model
Domestic cats, 280-day study
Treatment
Oral mibolerone, two daily regimens and one weekly regimen; doses not reproduced on this page
Follow-up
280 days; estrus assessed over 180 days
Study design
Controlled veterinary study
Funding
not stated in the source

The one behavioral observation in the mibolerone literature, and it is a null result.

Read the original source
Schedule III and WADA S1.1

Regulatory record

Electronic Code of Federal Regulations, Title 21, section 1308.13, Schedule III. World Anti-Doping Agency, The 2026 Prohibited List, in effect 1 January 2026.

21 CFR 1308.13(f)(63) lists mibolerone (7alpha,17alpha-dimethyl-17beta-hydroxyestr-4-en-3-one) among anabolic steroids in Schedule III, DEA code 4000, covering salts, esters and ethers. The WADA 2026 Prohibited List names mibolerone under S1.1, anabolic androgenic steroids, prohibited at all times as a non-specified substance. S0 separately prohibits substances approved only for veterinary use, which is mibolerone's status.

Participants / model
Regulatory and anti-doping records, not a population
Treatment
Not applicable
Follow-up
Current eCFR; WADA list in effect 1 January 2026
Study design
Codified federal regulation and official anti-doping record
Funding
not stated in the source

Legal status outside the United States is not covered.

Read the original source
No human drug application found

Regulatory record

openFDA Drugs@FDA API, substance_name MIBOLERONE, queried 9 October 2026. DailyMed search run the same day.

An openFDA Drugs@FDA substance-name query for MIBOLERONE returned no matches on 9 October 2026, and a DailyMed search returned no human label. The only codified US approvals are the two veterinary entries in 21 CFR 520.1430 and 21 CFR 558.348.

Participants / model
Regulatory records, not a population
Treatment
Not applicable
Follow-up
Query run on 9 October 2026
Study design
Official FDA API query
Funding
not stated in the source

Shows the absence of any human marketing authorization in the US record.

Read the original source
PubMed: 248 records, no human study

PubMed search record

PubMed search for mibolerone, run 9 October 2026, then restricted to the clinical trial publication type.

A PubMed search for mibolerone returned 248 records. Restricting to the clinical trial publication type returned exactly 1 record, a controlled blind-labeled field trial of mibolerone for pseudopregnancy in 63 bitches plus 17 placebo controls. Restricting to humans with clinical trial or randomized controlled trial publication types returned 0 records. The large human-indexed literature on mibolerone is laboratory work, where tritiated mibolerone is used as a radioligand to measure androgen receptor binding in human tissue and cell lines.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature search
Funding
not stated in the source

An absence finding as of 9 October 2026. Mibolerone has not been studied in a person in these records.

Read the original source
PubMed: 2 records on aggression, neither an outcome

PubMed search record

PubMed search for mibolerone combined with aggression or aggressive, run 9 October 2026. A second search combined mibolerone with strength, performance, muscle mass, athlete or doping.

A PubMed search for mibolerone with aggression or aggressive returned 2 records. Neither reports an aggression outcome from mibolerone in any species: one is the greyhound urinary metabolite study and the other is a single-dog veterinary behavior case report about aggression after ovariohysterectomy, with no abstract indexed. A search for mibolerone with strength, performance, muscle mass, athlete or doping returned 19 records, which are receptor-biology papers plus the greyhound metabolite study. The one behavioral observation in the entire mibolerone literature is the cat study, which recorded no behavioral change.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature search
Funding
not stated in the source

No evidence that mibolerone increases aggression, focus or performance in any species, and none at all in people.

Read the original source

Why is Mibolerone in F tier?

F fits a compound whose published downside outweighs any reported upside. The record is a veterinary estrus suppressant for dogs, and what it documents is clitoral enlargement in dogs and cats, masculinized female offspring, thyroid changes in cats and ovarian fibromas in 12 of 92 dogs on long-term dosing. The claimed aggression and focus benefit has no support in any species, and the one behavioral observation is a null result in cats. It is a Schedule III androgen with no human study of any kind.