Mesterolone
Mesterolone is the oral androgen in Proviron tablets, authorized in Spain for documented male androgen deficiency and hypogonadism-associated infertility. The regulated tablet has human pharmacokinetic data. Controlled idiopathic-infertility trials were negative or inconclusive, and no human trial supports aromatase inhibition, post-cycle recovery, muscle gain, strength, or athletic performance.
oral dihydrotestosterone-derived androgen
- Proviron is a brand name for mesterolone, an oral DHT-derived steroidal androgen.
- Spain authorizes the tablet for documented adult male androgen deficiency and hypogonadism-associated infertility.
- Three controlled idiopathic-infertility trials did not show a convincing pregnancy benefit.
- Binding SHBG and being non-aromatizable do not prove higher free testosterone or aromatase inhibition.
- A 2025 seized-product study found only two of four mesterolone-labeled samples contained mesterolone alone.
Are Proviron and mesterolone the same drug?
Yes when Proviron refers to the authorized 25 mg Bayer tablet: mesterolone is its active ingredient. Mesterolone is a methylated dihydrotestosterone derivative and an oral steroidal androgen, not a peptide, testosterone precursor, aromatase inhibitor, or SARM.
The Spanish product information and PubChem record anchor the medicine and molecule identities. An online product using the brand or generic name is not thereby authenticated as the authorized tablet.
AEMPS · current Spanish product information
Official national product information
Agencia Española de Medicamentos y Productos Sanitarios and Bayer. Proviron 25 mg tablets, text revision January 2023.
The official Spanish label identifies mesterolone 25 mg tablets, narrow adult-male indications, contraindications, adverse effects, interaction cautions, abuse risks, and formulation-specific pharmacokinetics including about 3% oral bioavailability and a 12-to-13-hour terminal half-life.
- Participants / model
- Adult men within the labeled indications
- Treatment
- Authorized Proviron 25 mg oral tablets
- Follow-up
- According to indication and medical supervision; no self-use protocol inferred
- Study design
- Regulatory product information
- Funding
- Bayer product authorization
The authorization is Spanish and product-specific; it is not an FDA label or evidence for bodybuilding use.
Read the original sourcePubChem · chemical identity
Official chemical identity record
National Center for Biotechnology Information. PubChem CID 15020.
The record identifies mesterolone with formula C20H32O2, molecular weight 304.5 g/mol, CAS 1424-00-6, and UNII 0SRQ75X9I9.
- Study design
- Chemical database record
Identity registration is not evidence of approval or a product's contents.
Read the original sourceWhat is Proviron authorized to treat?
Spain's current product information authorizes mesterolone for androgen replacement in adult men with androgen deficiency and for male infertility associated with male hypogonadism. The cited U.S. FDA records list no approval or labeled indication for idiopathic infertility, age-related optimization, physique use, or post-cycle treatment.
The label lists first authorization on 1 February 1970 and a January 2023 text revision. Its indications and safety instructions apply to that regulated product and jurisdiction.
AEMPS · current Spanish product information
Official national product information
Agencia Española de Medicamentos y Productos Sanitarios and Bayer. Proviron 25 mg tablets, text revision January 2023.
The official Spanish label identifies mesterolone 25 mg tablets, narrow adult-male indications, contraindications, adverse effects, interaction cautions, abuse risks, and formulation-specific pharmacokinetics including about 3% oral bioavailability and a 12-to-13-hour terminal half-life.
- Participants / model
- Adult men within the labeled indications
- Treatment
- Authorized Proviron 25 mg oral tablets
- Follow-up
- According to indication and medical supervision; no self-use protocol inferred
- Study design
- Regulatory product information
- Funding
- Bayer product authorization
The authorization is Spanish and product-specific; it is not an FDA label or evidence for bodybuilding use.
Read the original sourceWADA 2026 · mesterolone named
Official anti-doping standard
World Anti-Doping Agency. The 2026 Prohibited List, effective 1 January 2026.
Section S1.1 explicitly names mesterolone among anabolic androgenic steroids prohibited at all times.
- Participants / model
- Athletes subject to the World Anti-Doping Code
- Follow-up
- Calendar year 2026
- Study design
- Anti-doping prohibited list
- Funding
- World Anti-Doping Agency
Sport prohibition is separate from national medicine authorization.
Read the original sourceDoes mesterolone improve libido, mood, or low-testosterone symptoms?
A 34-man uncontrolled study reported improved symptom and urinary scores over two months, while total and calculated available testosterone fell. In a four-week randomized comparison, testosterone undecanoate produced better libido, erection, ejaculation, and mental-state scores than mesterolone. A 52-man placebo-controlled depression trial found no meaningful treatment-placebo difference.
| Study | Population and design | Result | Limit |
|---|---|---|---|
| Luisi and Franchi 1980 | 26 hypogonadal men; randomized double-blind double-dummy; four weeks | Testosterone undecanoate beat mesterolone at week four for libido (p<.001), erections (p<.01), ejaculation (p<.05), and mental state (p<.001) | Tiny, short, subjective outcomes, no placebo |
| Dugeroglu 2014 | 34 men with symptoms and/or total T <300 ng/dL; uncontrolled; two months | AMS 48.62→30.06; IPSS 17.44→8.44; prostate QoL 4.32→2.56 | No control or blinding; broad entry criteria; multiple outcomes |
| Itil 1984 | 52 male depressed outpatients; double-blind placebo-controlled; six weeks | Both groups improved; no statistically appreciable difference. Total and protein-bound testosterone fell with mesterolone. | Specialized depression population and old study; no modern replication |
Luisi and Franchi · four-week active comparison
Randomized double-blind active-comparator trial
Luisi M, Franchi F. Journal of Endocrinological Investigation. 1980;3(3):305-308. DOI 10.1007/BF03348281.
Twenty-six hypogonadal men were randomized in a double-dummy design to testosterone undecanoate or mesterolone for four weeks. Testosterone undecanoate produced significantly better week-four libido, erection, ejaculation, and mental-state scores.
- Participants / model
- 26 hypogonadal men aged 21 to 41; testosterone undecanoate n=12 and mesterolone n=14
- Treatment
- Oral testosterone undecanoate or oral mesterolone in double-dummy capsules
- Follow-up
- 4 weeks after withdrawal of injectable testosterone for at least 3 weeks
- Study design
- Randomized, double-blind, double-dummy active-comparator trial
- Funding
- Italian National Research Council grant
The trial had no placebo, used short subjective scales in heterogeneous hypogonadal diagnoses, measured no post-treatment hormone or performance endpoint, and did not describe systematic adverse-event collection.
Read the original sourceDugeroglu et al. · uncontrolled symptom and hormone study
Prospective uncontrolled clinical study
Dugeroglu H, Ozturk M, Atmaca M, Seven I. Journal of the Pakistan Medical Association. 2014;64(12):1366-1369. PMID 25842579.
AMS fell 48.62→30.06, IPSS 17.44→8.44, and prostate QoL 4.32→2.56. Total testosterone fell 436.73→352.48 ng/dL, SHBG 48.76→40.65 nmol/L, calculated free and bioavailable testosterone fell, and RIA free testosterone was unchanged (p=.337). Mean prostate volume and PSA did not change significantly.
- Participants / model
- 34 men, mean age 43±12, with aging-male symptoms and/or total testosterone below 300 ng/dL
- Treatment
- Oral mesterolone
- Follow-up
- 2 months
- Study design
- Prospective uncontrolled before-after study
No randomization, comparator, or blinding; broad entry criteria, multiple outcomes, and exclusion of known heart disease or suspected prostate cancer. Funding and conflicts are not reported in the cited publication.
Read the original sourceItil et al. · placebo-controlled depression trial
Randomized double-blind placebo-controlled trial
Itil TM, et al. Methods and Findings in Experimental and Clinical Pharmacology. 1984;6(6):331-337. PMID 6431212.
Both treatment and placebo groups improved over six weeks, with no statistically appreciable difference. Mesterolone lowered total and protein-bound testosterone.
- Participants / model
- 52 male depressed outpatients aged 26 to 53
- Treatment
- Mesterolone versus placebo
- Follow-up
- 6 weeks
- Study design
- Double-blind placebo-controlled trial
The population, high research exposure, and old EEG rationale do not establish a general mood or energy benefit.
Read the original sourceDoes mesterolone improve pregnancy rates or semen quality in idiopathic male infertility?
The three controlled fertility trials did not show a convincing pregnancy benefit. The 248-couple WHO trial found numerically higher pregnancy estimates at the higher mesterolone group, but confidence intervals included no effect. A 368-man randomized comparison and a 52-man placebo trial were also negative.
| Evidence | Population and design | Duration | Result and limit |
|---|---|---|---|
| WHO randomized trial | 248 couples randomized at seven centers; 157 met strict eligibility; double blind against placebo | Six months; pregnancy followed through eight months | Pregnancy estimates were 9%, 12%, and 16% in all randomized couples; confidence intervals included no effect and semen measures did not favor mesterolone; abstract only |
| Scottish randomized trial | 368 men; mesterolone versus vitamin C | Nine months | No pregnancy-rate difference overall or in the reported low-testosterone or low-sperm subgroup; abstract only |
| Gerris placebo trial | 52 men; double blind against placebo | Twelve months | Pregnancy was 26% with mesterolone and 48% with placebo; motility and morphology improved similarly; abstract only |
| Varma and Patel cohort | 250 treated men plus 100 separately followed untreated men; nonrandomized and unblinded | Twelve months | Pregnancy was 115/250 versus 14/100, but treatment followed severity, attrition was substantial, and pregnancy stopped follow-up; causal attribution is weak |
The approved label's hypogonadism-associated infertility indication is narrower than idiopathic infertility in otherwise unexplained subfertility.
WHO trial · 248 randomized couples
Multicenter randomized placebo-controlled trial
World Health Organization Task Force on the Diagnosis and Treatment of Infertility. International Journal of Andrology. 1989;12(4):254-264. PMID 2680994.
At seven centers, 248 couples were randomized to placebo or two mesterolone groups for six months; 157 satisfied strict eligibility criteria. Eight-month pregnancy estimates were 9%, 12%, and 16% in all randomized couples and 11%, 12%, and 19% in the strict subset, but confidence intervals included no effect. Semen outcomes did not significantly favor mesterolone.
- Participants / model
- 248 couples with idiopathic male infertility randomized; 157 in strict eligible subset
- Treatment
- Placebo or oral mesterolone at two study levels
- Follow-up
- 6 months treatment; pregnancy assessment through 8 months
- Study design
- Double-blind multicenter randomized trial
- Funding
- World Health Organization program
The abstract supports the multicenter randomized pregnancy and semen non-result but does not provide enough detail to assess allocation, attrition, adverse-event collection, or center-level methods.
Read the original sourceScottish Infertility Group · 368-man randomized trial
Prospective randomized active-comparator infertility trial
Hargreave TB, Kyle KF, Baxby K, Rogers ACN, Scott R, Tolley DA, Abel BJ, Orr PS, Elton RA; Scottish Infertility Group. British Journal of Urology. 1984;56(6):740-744. DOI 10.1111/j.1464-410x.1984.tb06160.x.
In 368 men with infertile marriages, pregnancy rates did not differ between mesterolone and vitamin C over nine months, including the reported low-testosterone or low-sperm-count subgroup with partners of normal fertility.
- Participants / model
- 368 men in infertile marriages
- Treatment
- Mesterolone versus vitamin C
- Follow-up
- 9 months
- Study design
- Prospective randomized active-comparator trial
The abstract reports the pregnancy non-result but does not provide enough detail to assess allocation concealment, attrition, adverse events, or numerical subgroup estimates.
Read the original sourceGerris et al. · 52-man placebo trial
Double-blind placebo-controlled infertility trial
Gerris J, Comhaire F, Hellemans P, Peeters K, Schoonjans F. Fertility and Sterility. 1991;55(3):603-607. DOI 10.1016/S0015-0282(16)54193-4.
Fifty-two men received mesterolone or placebo for 12 months. The abstract reports pregnancy in 26% of mesterolone couples and 48% of placebo couples, while motility and morphology improved similarly in both groups.
- Participants / model
- 52 men with idiopathic infertility
- Treatment
- Oral mesterolone versus placebo
- Follow-up
- 12 months
- Study design
- Double-blind placebo-controlled trial; the cited abstract does not report the allocation method
The abstract supports the negative result but does not provide enough detail to verify randomization, attrition, adverse-event collection, or exact denominators.
Read the original sourceVarma and Patel · nonrandomized controlled cohort
Nonrandomized controlled clinical cohort
Varma TR, Patel RH. International Journal of Gynaecology and Obstetrics. 1988;26(1):121-128. DOI 10.1016/0020-7292(88)90206-8.
The study followed 250 treated men and a separate 100-man untreated comparison cohort for one year. Pregnancy occurred in 115 of 250 treated couples and 14 of 100 untreated couples; semen measures improved in the moderate-oligospermia subgroup but not the severe subgroup. Attrition and pregnancy-related stopping reduced the denominators over time.
- Participants / model
- 250 treated men aged 22 to 46 with idiopathic oligospermia or oligoasthenospermia; 100 untreated men followed separately
- Treatment
- Oral mesterolone in clinical dose groups
- Follow-up
- 12 months
- Study design
- Nonrandomized, unblinded controlled cohort with repeated semen and hormone measures
The untreated cohort was not randomized, baseline comparability was incompletely reported, treatment differed by baseline severity, pregnancy stopped treatment, and paired analyses used diminishing follow-up samples. These limits prevent a causal pregnancy estimate.
Read the original sourceAEMPS · current Spanish product information
Official national product information
Agencia Española de Medicamentos y Productos Sanitarios and Bayer. Proviron 25 mg tablets, text revision January 2023.
The official Spanish label identifies mesterolone 25 mg tablets, narrow adult-male indications, contraindications, adverse effects, interaction cautions, abuse risks, and formulation-specific pharmacokinetics including about 3% oral bioavailability and a 12-to-13-hour terminal half-life.
- Participants / model
- Adult men within the labeled indications
- Treatment
- Authorized Proviron 25 mg oral tablets
- Follow-up
- According to indication and medical supervision; no self-use protocol inferred
- Study design
- Regulatory product information
- Funding
- Bayer product authorization
The authorization is Spanish and product-specific; it is not an FDA label or evidence for bodybuilding use.
Read the original sourceDoes mesterolone build muscle or work as an anti-estrogen?
No controlled human study in the cited evidence measured lean mass, hypertrophy, strength, power, endurance, or sport performance. Mesterolone activates the androgen receptor and animal muscle studies show biological activity, but they do not supply a human effect size. The product label says mesterolone is not converted to estrogen; no human study showed that it blocks aromatase or controls estrogen made from another androgen.
In the 2014 cohort, estradiol and SHBG fell together with total and calculated free or bioavailable testosterone. That pattern does not demonstrate aromatase inhibition.
AEMPS · current Spanish product information
Official national product information
Agencia Española de Medicamentos y Productos Sanitarios and Bayer. Proviron 25 mg tablets, text revision January 2023.
The official Spanish label identifies mesterolone 25 mg tablets, narrow adult-male indications, contraindications, adverse effects, interaction cautions, abuse risks, and formulation-specific pharmacokinetics including about 3% oral bioavailability and a 12-to-13-hour terminal half-life.
- Participants / model
- Adult men within the labeled indications
- Treatment
- Authorized Proviron 25 mg oral tablets
- Follow-up
- According to indication and medical supervision; no self-use protocol inferred
- Study design
- Regulatory product information
- Funding
- Bayer product authorization
The authorization is Spanish and product-specific; it is not an FDA label or evidence for bodybuilding use.
Read the original sourceHuman evidence · no controlled performance trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for mesterolone and human performance.
The cited records include fertility and androgen-use literature but no controlled human trial establishing muscle gain, strength, body-composition improvement, athletic performance, aromatase inhibition, or post-cycle recovery. ClinicalTrials.gov lists no exact-name intervention or title match.
- Participants / model
- Public indexed and registered human mesterolone evidence
Dugeroglu et al. · uncontrolled symptom and hormone study
Prospective uncontrolled clinical study
Dugeroglu H, Ozturk M, Atmaca M, Seven I. Journal of the Pakistan Medical Association. 2014;64(12):1366-1369. PMID 25842579.
AMS fell 48.62→30.06, IPSS 17.44→8.44, and prostate QoL 4.32→2.56. Total testosterone fell 436.73→352.48 ng/dL, SHBG 48.76→40.65 nmol/L, calculated free and bioavailable testosterone fell, and RIA free testosterone was unchanged (p=.337). Mean prostate volume and PSA did not change significantly.
- Participants / model
- 34 men, mean age 43±12, with aging-male symptoms and/or total testosterone below 300 ng/dL
- Treatment
- Oral mesterolone
- Follow-up
- 2 months
- Study design
- Prospective uncontrolled before-after study
No randomization, comparator, or blinding; broad entry criteria, multiple outcomes, and exclusion of known heart disease or suspected prostate cancer. Funding and conflicts are not reported in the cited publication.
Read the original sourceDoes SHBG binding raise testosterone, or does mesterolone restart the axis after AAS?
Neither claim has direct outcome support. In ten healthy men, total testosterone fell from about 5.2 to 4.0 and then 3.5 ng/mL across two four-week periods; the study's free-testosterone estimate did not materially rise. The 2014 cohort also recorded lower total, calculated free, and calculated bioavailable testosterone. The cited evidence includes no mesterolone-specific post-AAS hormone, symptom, semen, or fertility recovery trial.
Mesterolone appears in illicit PCT products, which documents a use pattern. It does not show recovery efficacy. As an exogenous androgen, it cannot be assumed to restart LH and FSH.
Aakvaag and Strømme · healthy-men hormone study
Small sequential clinical pharmacology study
Aakvaag A, Strømme SB. Acta Endocrinologica. 1974;77(2):380-386. PMID 4479415. DOI 10.1530/acta.0.0770380.
In ten healthy men, total testosterone fell from about 5.2 to 4.0 and then 3.5 ng/mL across sequential four-week periods. LH and FSH changed little; a diluted-plasma free-testosterone estimate changed from 0.37 to 0.41 ng/mL.
- Participants / model
- 10 healthy men
- Treatment
- Sequential lower and higher mesterolone exposure
- Follow-up
- 8 weeks
- Study design
- Uncontrolled sequential clinical pharmacology study
This small older study used a diluted-plasma free-testosterone method; it does not show clinical benefit or post-AAS recovery.
Read the original sourceDugeroglu et al. · uncontrolled symptom and hormone study
Prospective uncontrolled clinical study
Dugeroglu H, Ozturk M, Atmaca M, Seven I. Journal of the Pakistan Medical Association. 2014;64(12):1366-1369. PMID 25842579.
AMS fell 48.62→30.06, IPSS 17.44→8.44, and prostate QoL 4.32→2.56. Total testosterone fell 436.73→352.48 ng/dL, SHBG 48.76→40.65 nmol/L, calculated free and bioavailable testosterone fell, and RIA free testosterone was unchanged (p=.337). Mean prostate volume and PSA did not change significantly.
- Participants / model
- 34 men, mean age 43±12, with aging-male symptoms and/or total testosterone below 300 ng/dL
- Treatment
- Oral mesterolone
- Follow-up
- 2 months
- Study design
- Prospective uncontrolled before-after study
No randomization, comparator, or blinding; broad entry criteria, multiple outcomes, and exclusion of known heart disease or suspected prostate cancer. Funding and conflicts are not reported in the cited publication.
Read the original sourceBlazewicz et al. · seized PCT product testing
Official-laboratory analytical study
Blazewicz A, Poplawska M, Daniszewska B, Piorunska K, Karynski M. Frontiers in Chemistry. 2025;13:1536858. PMID 40177353. DOI 10.3389/fchem.2025.1536858.
The Polish official laboratory tested 601 seized PED samples, including 63 labeled PCT products. Of four labeled mesterolone, two contained mesterolone alone, one contained stanozolol plus sildenafil, and one contained no active ingredient.
- Participants / model
- 601 police- or prosecutor-seized performance-enhancing product samples collected in Poland from 2020 through August 2024
- Treatment
- Laboratory identity testing; no human administration
- Follow-up
- Samples collected 2020 to 2024
- Study design
- Cross-sectional qualitative chemical analysis of seized products
The seizure sample is not representative of all products or sellers. It documents identity failure and PCT marketing, not recovery efficacy. Authors declared no commercial or financial conflict.
Read the original sourceHuman evidence · no controlled performance trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for mesterolone and human performance.
The cited records include fertility and androgen-use literature but no controlled human trial establishing muscle gain, strength, body-composition improvement, athletic performance, aromatase inhibition, or post-cycle recovery. ClinicalTrials.gov lists no exact-name intervention or title match.
- Participants / model
- Public indexed and registered human mesterolone evidence
What human pharmacokinetics are stated?
The Spanish label reports rapid absorption after the authorized oral tablet but only about 3% oral bioavailability. After one 25 mg tablet, the reported peak was 3.1 plus or minus 1.1 ng/mL at 1.6 plus or minus 0.6 hours, and terminal half-life was 12 to 13 hours. The label does not give the participant count or population for those values.
The label also reports about 98% protein binding, divided between albumin and SHBG, and mostly metabolite excretion. These data describe the authorized tablet; they do not authenticate an unregulated product or establish an effect duration.
AEMPS · current Spanish product information
Official national product information
Agencia Española de Medicamentos y Productos Sanitarios and Bayer. Proviron 25 mg tablets, text revision January 2023.
The official Spanish label identifies mesterolone 25 mg tablets, narrow adult-male indications, contraindications, adverse effects, interaction cautions, abuse risks, and formulation-specific pharmacokinetics including about 3% oral bioavailability and a 12-to-13-hour terminal half-life.
- Participants / model
- Adult men within the labeled indications
- Treatment
- Authorized Proviron 25 mg oral tablets
- Follow-up
- According to indication and medical supervision; no self-use protocol inferred
- Study design
- Regulatory product information
- Funding
- Bayer product authorization
The authorization is Spanish and product-specific; it is not an FDA label or evidence for bodybuilding use.
Read the original sourceWhat are the official contraindications, adverse effects, and interaction concerns?
The Spanish label lists prostate and liver contraindications and reports acne, alopecia, headache, abdominal pain, increased erections or priapism, and benign or malignant liver tumors. It warns that androgen abuse, often in combination, can cause severe or fatal cardiovascular, hepatic, psychiatric, and dependence-related harm. No mesterolone-specific interaction study was performed, and small short trials cannot establish long-term safety.
The label gives class-based cautions involving enzyme inducers or inhibitors, coumarin anticoagulants, diabetes medicines, ACTH or corticosteroids, cyclosporine, thyroid tests, neuromuscular blockers, bupropion, and other hepatotoxic agents.
A six-week mouse study found adverse lipoprotein, troponin, blood-pressure, and cardiac-remodeling changes. It cannot estimate human incidence.
A Polish official laboratory tested 601 seized performance-enhancing products. Four were labeled mesterolone: two contained mesterolone alone, one contained stanozolol plus sildenafil, and one contained no active ingredient. The seized sample is not a random market survey.
AEMPS · current Spanish product information
Official national product information
Agencia Española de Medicamentos y Productos Sanitarios and Bayer. Proviron 25 mg tablets, text revision January 2023.
The official Spanish label identifies mesterolone 25 mg tablets, narrow adult-male indications, contraindications, adverse effects, interaction cautions, abuse risks, and formulation-specific pharmacokinetics including about 3% oral bioavailability and a 12-to-13-hour terminal half-life.
- Participants / model
- Adult men within the labeled indications
- Treatment
- Authorized Proviron 25 mg oral tablets
- Follow-up
- According to indication and medical supervision; no self-use protocol inferred
- Study design
- Regulatory product information
- Funding
- Bayer product authorization
The authorization is Spanish and product-specific; it is not an FDA label or evidence for bodybuilding use.
Read the original sourceFontana et al. · transgenic mouse cardiovascular study
Controlled animal toxicology and exercise study
Fontana K, Oliveira HCF, Leonardo MB, Mandarim-de-Lacerda CA, da Cruz-Höfling MA. International Journal of Experimental Pathology. 2008;89(5):358-366. DOI 10.1111/j.1365-2613.2008.00601.x.
Twenty-four male mice with a human-like lipemic transgenic phenotype were divided into four groups of six. Mesterolone increased atherogenic lipoproteins and troponin T and altered blood pressure and cardiac remodeling; treadmill training attenuated some findings.
- Participants / model
- 24 adult male CETP-expressing LDL-receptor-knockout mice; four groups of six
- Treatment
- Mesterolone or vehicle during the last three weeks of a six-week sedentary or treadmill protocol
- Follow-up
- 6 weeks; mesterolone during the final 3 weeks
- Study design
- Controlled two-factor mouse exercise and toxicology study
- Funding
- Brazilian academic funding listed in the paper
The small genetically modified mouse model cannot provide a human event rate. It is a compound-specific preclinical cardiovascular signal.
Read the original sourceBlazewicz et al. · seized PCT product testing
Official-laboratory analytical study
Blazewicz A, Poplawska M, Daniszewska B, Piorunska K, Karynski M. Frontiers in Chemistry. 2025;13:1536858. PMID 40177353. DOI 10.3389/fchem.2025.1536858.
The Polish official laboratory tested 601 seized PED samples, including 63 labeled PCT products. Of four labeled mesterolone, two contained mesterolone alone, one contained stanozolol plus sildenafil, and one contained no active ingredient.
- Participants / model
- 601 police- or prosecutor-seized performance-enhancing product samples collected in Poland from 2020 through August 2024
- Treatment
- Laboratory identity testing; no human administration
- Follow-up
- Samples collected 2020 to 2024
- Study design
- Cross-sectional qualitative chemical analysis of seized products
The seizure sample is not representative of all products or sellers. It documents identity failure and PCT marketing, not recovery efficacy. Authors declared no commercial or financial conflict.
Read the original sourceWhy is mesterolone B tier?
B for human evidence depth: mesterolone has a regulated tablet, product-specific PK, and several controlled human studies. The stronger infertility trials are negative or inconclusive, testosterone undecanoate performed better in a short replacement comparison, and no direct human trial supports aromatase inhibition, post-cycle recovery, muscle gain, strength, or athletic performance.
AEMPS · current Spanish product information
Official national product information
Agencia Española de Medicamentos y Productos Sanitarios and Bayer. Proviron 25 mg tablets, text revision January 2023.
The official Spanish label identifies mesterolone 25 mg tablets, narrow adult-male indications, contraindications, adverse effects, interaction cautions, abuse risks, and formulation-specific pharmacokinetics including about 3% oral bioavailability and a 12-to-13-hour terminal half-life.
- Participants / model
- Adult men within the labeled indications
- Treatment
- Authorized Proviron 25 mg oral tablets
- Follow-up
- According to indication and medical supervision; no self-use protocol inferred
- Study design
- Regulatory product information
- Funding
- Bayer product authorization
The authorization is Spanish and product-specific; it is not an FDA label or evidence for bodybuilding use.
Read the original sourceWHO trial · 248 randomized couples
Multicenter randomized placebo-controlled trial
World Health Organization Task Force on the Diagnosis and Treatment of Infertility. International Journal of Andrology. 1989;12(4):254-264. PMID 2680994.
At seven centers, 248 couples were randomized to placebo or two mesterolone groups for six months; 157 satisfied strict eligibility criteria. Eight-month pregnancy estimates were 9%, 12%, and 16% in all randomized couples and 11%, 12%, and 19% in the strict subset, but confidence intervals included no effect. Semen outcomes did not significantly favor mesterolone.
- Participants / model
- 248 couples with idiopathic male infertility randomized; 157 in strict eligible subset
- Treatment
- Placebo or oral mesterolone at two study levels
- Follow-up
- 6 months treatment; pregnancy assessment through 8 months
- Study design
- Double-blind multicenter randomized trial
- Funding
- World Health Organization program
The abstract supports the multicenter randomized pregnancy and semen non-result but does not provide enough detail to assess allocation, attrition, adverse-event collection, or center-level methods.
Read the original sourceScottish Infertility Group · 368-man randomized trial
Prospective randomized active-comparator infertility trial
Hargreave TB, Kyle KF, Baxby K, Rogers ACN, Scott R, Tolley DA, Abel BJ, Orr PS, Elton RA; Scottish Infertility Group. British Journal of Urology. 1984;56(6):740-744. DOI 10.1111/j.1464-410x.1984.tb06160.x.
In 368 men with infertile marriages, pregnancy rates did not differ between mesterolone and vitamin C over nine months, including the reported low-testosterone or low-sperm-count subgroup with partners of normal fertility.
- Participants / model
- 368 men in infertile marriages
- Treatment
- Mesterolone versus vitamin C
- Follow-up
- 9 months
- Study design
- Prospective randomized active-comparator trial
The abstract reports the pregnancy non-result but does not provide enough detail to assess allocation concealment, attrition, adverse events, or numerical subgroup estimates.
Read the original sourceGerris et al. · 52-man placebo trial
Double-blind placebo-controlled infertility trial
Gerris J, Comhaire F, Hellemans P, Peeters K, Schoonjans F. Fertility and Sterility. 1991;55(3):603-607. DOI 10.1016/S0015-0282(16)54193-4.
Fifty-two men received mesterolone or placebo for 12 months. The abstract reports pregnancy in 26% of mesterolone couples and 48% of placebo couples, while motility and morphology improved similarly in both groups.
- Participants / model
- 52 men with idiopathic infertility
- Treatment
- Oral mesterolone versus placebo
- Follow-up
- 12 months
- Study design
- Double-blind placebo-controlled trial; the cited abstract does not report the allocation method
The abstract supports the negative result but does not provide enough detail to verify randomization, attrition, adverse-event collection, or exact denominators.
Read the original sourceLuisi and Franchi · four-week active comparison
Randomized double-blind active-comparator trial
Luisi M, Franchi F. Journal of Endocrinological Investigation. 1980;3(3):305-308. DOI 10.1007/BF03348281.
Twenty-six hypogonadal men were randomized in a double-dummy design to testosterone undecanoate or mesterolone for four weeks. Testosterone undecanoate produced significantly better week-four libido, erection, ejaculation, and mental-state scores.
- Participants / model
- 26 hypogonadal men aged 21 to 41; testosterone undecanoate n=12 and mesterolone n=14
- Treatment
- Oral testosterone undecanoate or oral mesterolone in double-dummy capsules
- Follow-up
- 4 weeks after withdrawal of injectable testosterone for at least 3 weeks
- Study design
- Randomized, double-blind, double-dummy active-comparator trial
- Funding
- Italian National Research Council grant
The trial had no placebo, used short subjective scales in heterogeneous hypogonadal diagnoses, measured no post-treatment hormone or performance endpoint, and did not describe systematic adverse-event collection.
Read the original sourceHuman evidence · no controlled performance trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for mesterolone and human performance.
The cited records include fertility and androgen-use literature but no controlled human trial establishing muscle gain, strength, body-composition improvement, athletic performance, aromatase inhibition, or post-cycle recovery. ClinicalTrials.gov lists no exact-name intervention or title match.
- Participants / model
- Public indexed and registered human mesterolone evidence
Do Chinese- or Russian-language records add clinical or preclinical mesterolone evidence?
The cited Chinese and Russian records include no mesterolone treatment study. One Chinese-language paper validated a mass-spectrometry method that included mesterolone, 美睾酮, among 50 analytes in livestock meat. It administered no mesterolone to people or animals and supplied no efficacy, pharmacokinetic, or clinical-safety result.
The Chinese-language record was an analytical-method paper, not a treatment study. Russian-language records were medicine monographs, reviews, conference translations, or secondary pages; some records provided only snippets or index metadata.
Feng et al. · Chinese meat-matrix assay
Chinese-language analytical-method study
Feng Y, Wang J, Hou F, Ding Q, Chu H, Liu Y. 色谱 / Chinese Journal of Chromatography. 2022;40(5):409-422. DOI 10.3724/SP.J.1123.2021.12005.
The full Chinese paper developed and validated a QuEChERS-UPLC-MS/MS panel for 50 food-borne stimulant and hormone analytes in livestock and poultry meat. Mesterolone, labeled 美睾酮, was an analytical target and was chromatographically separated from the isomer mestanolone.
- Participants / model
- Spiked and market livestock/poultry meat samples
- Treatment
- Analytical detection of mesterolone among a multi-analyte panel
- Study design
- Chinese-language analytical method validation
- Funding
- Chinese laboratory and food-safety research program
This Chinese analytical paper distinguishes mesterolone from mestanolone among 50 analytes in livestock meat. It did not administer mesterolone to people or animals, so it provides no efficacy, pharmacokinetic, or clinical-safety evidence.
Read the original sourceChinese and Russian records · no additional treatment study
Literature and registry records
Chinese and Russian literature and registry records for mesterolone.
The cited Chinese records include an analytical paper but no clinical or preclinical treatment study. The cited Russian records include monographs and secondary literature but no administered-subject dataset. Together they add no human performance or pharmacokinetic evidence.
- Participants / model
- Chinese- and Russian-language public literature and registry records
The cited regional records are indexes or secondary accounts rather than clinical evidence. They cannot exclude unpublished work.
Read the original sourceStudies and sources
PubChem · chemical identity
Official chemical identity record
National Center for Biotechnology Information. PubChem CID 15020.
The record identifies mesterolone with formula C20H32O2, molecular weight 304.5 g/mol, CAS 1424-00-6, and UNII 0SRQ75X9I9.
- Study design
- Chemical database record
Identity registration is not evidence of approval or a product's contents.
Read the original sourceAEMPS · current Spanish product information
Official national product information
Agencia Española de Medicamentos y Productos Sanitarios and Bayer. Proviron 25 mg tablets, text revision January 2023.
The official Spanish label identifies mesterolone 25 mg tablets, narrow adult-male indications, contraindications, adverse effects, interaction cautions, abuse risks, and formulation-specific pharmacokinetics including about 3% oral bioavailability and a 12-to-13-hour terminal half-life.
- Participants / model
- Adult men within the labeled indications
- Treatment
- Authorized Proviron 25 mg oral tablets
- Follow-up
- According to indication and medical supervision; no self-use protocol inferred
- Study design
- Regulatory product information
- Funding
- Bayer product authorization
The authorization is Spanish and product-specific; it is not an FDA label or evidence for bodybuilding use.
Read the original sourceWHO trial · 248 randomized couples
Multicenter randomized placebo-controlled trial
World Health Organization Task Force on the Diagnosis and Treatment of Infertility. International Journal of Andrology. 1989;12(4):254-264. PMID 2680994.
At seven centers, 248 couples were randomized to placebo or two mesterolone groups for six months; 157 satisfied strict eligibility criteria. Eight-month pregnancy estimates were 9%, 12%, and 16% in all randomized couples and 11%, 12%, and 19% in the strict subset, but confidence intervals included no effect. Semen outcomes did not significantly favor mesterolone.
- Participants / model
- 248 couples with idiopathic male infertility randomized; 157 in strict eligible subset
- Treatment
- Placebo or oral mesterolone at two study levels
- Follow-up
- 6 months treatment; pregnancy assessment through 8 months
- Study design
- Double-blind multicenter randomized trial
- Funding
- World Health Organization program
The abstract supports the multicenter randomized pregnancy and semen non-result but does not provide enough detail to assess allocation, attrition, adverse-event collection, or center-level methods.
Read the original sourceVarma and Patel · nonrandomized controlled cohort
Nonrandomized controlled clinical cohort
Varma TR, Patel RH. International Journal of Gynaecology and Obstetrics. 1988;26(1):121-128. DOI 10.1016/0020-7292(88)90206-8.
The study followed 250 treated men and a separate 100-man untreated comparison cohort for one year. Pregnancy occurred in 115 of 250 treated couples and 14 of 100 untreated couples; semen measures improved in the moderate-oligospermia subgroup but not the severe subgroup. Attrition and pregnancy-related stopping reduced the denominators over time.
- Participants / model
- 250 treated men aged 22 to 46 with idiopathic oligospermia or oligoasthenospermia; 100 untreated men followed separately
- Treatment
- Oral mesterolone in clinical dose groups
- Follow-up
- 12 months
- Study design
- Nonrandomized, unblinded controlled cohort with repeated semen and hormone measures
The untreated cohort was not randomized, baseline comparability was incompletely reported, treatment differed by baseline severity, pregnancy stopped treatment, and paired analyses used diminishing follow-up samples. These limits prevent a causal pregnancy estimate.
Read the original sourceHuman evidence · no controlled performance trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for mesterolone and human performance.
The cited records include fertility and androgen-use literature but no controlled human trial establishing muscle gain, strength, body-composition improvement, athletic performance, aromatase inhibition, or post-cycle recovery. ClinicalTrials.gov lists no exact-name intervention or title match.
- Participants / model
- Public indexed and registered human mesterolone evidence
WADA 2026 · mesterolone named
Official anti-doping standard
World Anti-Doping Agency. The 2026 Prohibited List, effective 1 January 2026.
Section S1.1 explicitly names mesterolone among anabolic androgenic steroids prohibited at all times.
- Participants / model
- Athletes subject to the World Anti-Doping Code
- Follow-up
- Calendar year 2026
- Study design
- Anti-doping prohibited list
- Funding
- World Anti-Doping Agency
Sport prohibition is separate from national medicine authorization.
Read the original sourceFeng et al. · Chinese meat-matrix assay
Chinese-language analytical-method study
Feng Y, Wang J, Hou F, Ding Q, Chu H, Liu Y. 色谱 / Chinese Journal of Chromatography. 2022;40(5):409-422. DOI 10.3724/SP.J.1123.2021.12005.
The full Chinese paper developed and validated a QuEChERS-UPLC-MS/MS panel for 50 food-borne stimulant and hormone analytes in livestock and poultry meat. Mesterolone, labeled 美睾酮, was an analytical target and was chromatographically separated from the isomer mestanolone.
- Participants / model
- Spiked and market livestock/poultry meat samples
- Treatment
- Analytical detection of mesterolone among a multi-analyte panel
- Study design
- Chinese-language analytical method validation
- Funding
- Chinese laboratory and food-safety research program
This Chinese analytical paper distinguishes mesterolone from mestanolone among 50 analytes in livestock meat. It did not administer mesterolone to people or animals, so it provides no efficacy, pharmacokinetic, or clinical-safety evidence.
Read the original sourceChinese and Russian records · no additional treatment study
Literature and registry records
Chinese and Russian literature and registry records for mesterolone.
The cited Chinese records include an analytical paper but no clinical or preclinical treatment study. The cited Russian records include monographs and secondary literature but no administered-subject dataset. Together they add no human performance or pharmacokinetic evidence.
- Participants / model
- Chinese- and Russian-language public literature and registry records
The cited regional records are indexes or secondary accounts rather than clinical evidence. They cannot exclude unpublished work.
Read the original sourceLuisi and Franchi · four-week active comparison
Randomized double-blind active-comparator trial
Luisi M, Franchi F. Journal of Endocrinological Investigation. 1980;3(3):305-308. DOI 10.1007/BF03348281.
Twenty-six hypogonadal men were randomized in a double-dummy design to testosterone undecanoate or mesterolone for four weeks. Testosterone undecanoate produced significantly better week-four libido, erection, ejaculation, and mental-state scores.
- Participants / model
- 26 hypogonadal men aged 21 to 41; testosterone undecanoate n=12 and mesterolone n=14
- Treatment
- Oral testosterone undecanoate or oral mesterolone in double-dummy capsules
- Follow-up
- 4 weeks after withdrawal of injectable testosterone for at least 3 weeks
- Study design
- Randomized, double-blind, double-dummy active-comparator trial
- Funding
- Italian National Research Council grant
The trial had no placebo, used short subjective scales in heterogeneous hypogonadal diagnoses, measured no post-treatment hormone or performance endpoint, and did not describe systematic adverse-event collection.
Read the original sourceScottish Infertility Group · 368-man randomized trial
Prospective randomized active-comparator infertility trial
Hargreave TB, Kyle KF, Baxby K, Rogers ACN, Scott R, Tolley DA, Abel BJ, Orr PS, Elton RA; Scottish Infertility Group. British Journal of Urology. 1984;56(6):740-744. DOI 10.1111/j.1464-410x.1984.tb06160.x.
In 368 men with infertile marriages, pregnancy rates did not differ between mesterolone and vitamin C over nine months, including the reported low-testosterone or low-sperm-count subgroup with partners of normal fertility.
- Participants / model
- 368 men in infertile marriages
- Treatment
- Mesterolone versus vitamin C
- Follow-up
- 9 months
- Study design
- Prospective randomized active-comparator trial
The abstract reports the pregnancy non-result but does not provide enough detail to assess allocation concealment, attrition, adverse events, or numerical subgroup estimates.
Read the original sourceGerris et al. · 52-man placebo trial
Double-blind placebo-controlled infertility trial
Gerris J, Comhaire F, Hellemans P, Peeters K, Schoonjans F. Fertility and Sterility. 1991;55(3):603-607. DOI 10.1016/S0015-0282(16)54193-4.
Fifty-two men received mesterolone or placebo for 12 months. The abstract reports pregnancy in 26% of mesterolone couples and 48% of placebo couples, while motility and morphology improved similarly in both groups.
- Participants / model
- 52 men with idiopathic infertility
- Treatment
- Oral mesterolone versus placebo
- Follow-up
- 12 months
- Study design
- Double-blind placebo-controlled trial; the cited abstract does not report the allocation method
The abstract supports the negative result but does not provide enough detail to verify randomization, attrition, adverse-event collection, or exact denominators.
Read the original sourceFontana et al. · transgenic mouse cardiovascular study
Controlled animal toxicology and exercise study
Fontana K, Oliveira HCF, Leonardo MB, Mandarim-de-Lacerda CA, da Cruz-Höfling MA. International Journal of Experimental Pathology. 2008;89(5):358-366. DOI 10.1111/j.1365-2613.2008.00601.x.
Twenty-four male mice with a human-like lipemic transgenic phenotype were divided into four groups of six. Mesterolone increased atherogenic lipoproteins and troponin T and altered blood pressure and cardiac remodeling; treadmill training attenuated some findings.
- Participants / model
- 24 adult male CETP-expressing LDL-receptor-knockout mice; four groups of six
- Treatment
- Mesterolone or vehicle during the last three weeks of a six-week sedentary or treadmill protocol
- Follow-up
- 6 weeks; mesterolone during the final 3 weeks
- Study design
- Controlled two-factor mouse exercise and toxicology study
- Funding
- Brazilian academic funding listed in the paper
The small genetically modified mouse model cannot provide a human event rate. It is a compound-specific preclinical cardiovascular signal.
Read the original sourceDugeroglu et al. · uncontrolled symptom and hormone study
Prospective uncontrolled clinical study
Dugeroglu H, Ozturk M, Atmaca M, Seven I. Journal of the Pakistan Medical Association. 2014;64(12):1366-1369. PMID 25842579.
AMS fell 48.62→30.06, IPSS 17.44→8.44, and prostate QoL 4.32→2.56. Total testosterone fell 436.73→352.48 ng/dL, SHBG 48.76→40.65 nmol/L, calculated free and bioavailable testosterone fell, and RIA free testosterone was unchanged (p=.337). Mean prostate volume and PSA did not change significantly.
- Participants / model
- 34 men, mean age 43±12, with aging-male symptoms and/or total testosterone below 300 ng/dL
- Treatment
- Oral mesterolone
- Follow-up
- 2 months
- Study design
- Prospective uncontrolled before-after study
No randomization, comparator, or blinding; broad entry criteria, multiple outcomes, and exclusion of known heart disease or suspected prostate cancer. Funding and conflicts are not reported in the cited publication.
Read the original sourceAakvaag and Strømme · healthy-men hormone study
Small sequential clinical pharmacology study
Aakvaag A, Strømme SB. Acta Endocrinologica. 1974;77(2):380-386. PMID 4479415. DOI 10.1530/acta.0.0770380.
In ten healthy men, total testosterone fell from about 5.2 to 4.0 and then 3.5 ng/mL across sequential four-week periods. LH and FSH changed little; a diluted-plasma free-testosterone estimate changed from 0.37 to 0.41 ng/mL.
- Participants / model
- 10 healthy men
- Treatment
- Sequential lower and higher mesterolone exposure
- Follow-up
- 8 weeks
- Study design
- Uncontrolled sequential clinical pharmacology study
This small older study used a diluted-plasma free-testosterone method; it does not show clinical benefit or post-AAS recovery.
Read the original sourceItil et al. · placebo-controlled depression trial
Randomized double-blind placebo-controlled trial
Itil TM, et al. Methods and Findings in Experimental and Clinical Pharmacology. 1984;6(6):331-337. PMID 6431212.
Both treatment and placebo groups improved over six weeks, with no statistically appreciable difference. Mesterolone lowered total and protein-bound testosterone.
- Participants / model
- 52 male depressed outpatients aged 26 to 53
- Treatment
- Mesterolone versus placebo
- Follow-up
- 6 weeks
- Study design
- Double-blind placebo-controlled trial
The population, high research exposure, and old EEG rationale do not establish a general mood or energy benefit.
Read the original sourceBlazewicz et al. · seized PCT product testing
Official-laboratory analytical study
Blazewicz A, Poplawska M, Daniszewska B, Piorunska K, Karynski M. Frontiers in Chemistry. 2025;13:1536858. PMID 40177353. DOI 10.3389/fchem.2025.1536858.
The Polish official laboratory tested 601 seized PED samples, including 63 labeled PCT products. Of four labeled mesterolone, two contained mesterolone alone, one contained stanozolol plus sildenafil, and one contained no active ingredient.
- Participants / model
- 601 police- or prosecutor-seized performance-enhancing product samples collected in Poland from 2020 through August 2024
- Treatment
- Laboratory identity testing; no human administration
- Follow-up
- Samples collected 2020 to 2024
- Study design
- Cross-sectional qualitative chemical analysis of seized products
The seizure sample is not representative of all products or sellers. It documents identity failure and PCT marketing, not recovery efficacy. Authors declared no commercial or financial conflict.
Read the original sourceWhy is Mesterolone in B tier?
B for human evidence depth: mesterolone has a regulated tablet, product-specific PK, and several controlled human studies. The stronger infertility trials are negative or inconclusive, testosterone undecanoate performed better in a short replacement comparison, and no direct human trial supports aromatase inhibition, post-cycle recovery, muscle gain, strength, or athletic performance.