Mesterolone (Proviron)

Mesterolone, almost always sold under the brand name Proviron, is a man-made oral steroid. More precisely, it’s an anabolic-androgenic steroid (AAS) — a synthetic relative of the male hormone dihydrotestosterone (DHT). It’s an androgen (a male-hormone-type drug), not a peptide and not a SARM. Unlike most of the drugs people mention it alongside, mesterolone was never approved or sold in the United States, so the usual shorthand that “these are mostly approved medicines” simply isn’t true here. Overseas, doctors mainly used it for low testosterone (male hypogonadism) and for male infertility with no clear cause. But the careful human studies on its two best-known medical uses — fertility and mood — came back negative or unconvincing, and its gym reputation as an “anti-estrogen” or a way to free up more testosterone has no solid human evidence behind it. This profile gives no doses, cycles, stacks, or post-cycle plans. It’s a reference, not a how-to.

What it is

Mesterolone (its official generic name, or INN) is a synthetic oral steroid in the DHT family. On paper its chemistry is 1α-methyl-DHT (1α-methyl-5α-androstan-17β-ol-3-one) — basically dihydrotestosterone with a small methyl group bolted on at one spot (the C1α position). That added methyl group lets the drug survive being swallowed: it resists “first-pass metabolism” (the liver’s habit of breaking down a drug before it reaches the bloodstream), so the pill actually works by mouth. Just as important, this means mesterolone is not 17α-alkylated. 17α-alkylation is the chemical tweak that gives many oral steroids — like methyltestosterone and stanozolol — their well-known liver toxicity. Because mesterolone doesn’t have that tweak, it doesn’t carry that obvious liver-damaging signature.

How does it work in the body? Mesterolone switches on the androgen receptor (AR) — the docking point cells use to respond to male hormones. Because it’s already a 5α-reduced DHT derivative, it is not a target for aromatase (the enzyme that turns testosterone into estrogen), so it doesn’t convert into estrogen and has no direct estrogen-like effects of its own. That non-converting trait, plus the fact that it binds tightly to sex hormone-binding globulin (SHBG — a protein in the blood that grabs onto hormones and keeps them inactive), is the rough basis for its reputation as an “anti-estrogen” or a “free-testosterone raiser.” But the actual clinical evidence for that effect is weak. Overall it leans much more toward androgenic effects than muscle-building ones, so it isn’t used to pack on large amounts of lean mass.

The claims

• Medical (outside the US): some historical, occasional use for low androgen levels, and — more controversially — for treating male infertility with no clear cause (oligospermia, meaning a low sperm count), a use that controlled evidence does not support.
• Physique/performance (off-label, illicit): that mesterolone’s SHBG binding raises “free testosterone,” acts as an “anti-estrogen,” boosts libido, and creates a “harder” look — rather than adding bulk.

None of these performance uses are backed by an approved medical indication or by strong human evidence that they work.

What the evidence actually shows

Male infertility — it does not clearly work. A double-blind, placebo-controlled trial (a study where neither patients nor doctors know who got the real drug, and some get a dummy pill for comparison) tested high-dose mesterolone in men with infertility of no clear cause (Gerris et al., Fertil Steril 1991). The pregnancy rate was actually lower in the mesterolone group than in the placebo group (about 26% vs 48%). Sperm numbers improved in the placebo group too, and the authors concluded their data “cast doubt on” whether the treatment helps at all. A larger double-blind, placebo-controlled study from the WHO Task Force (Int J Androl 1989) found only a small bump in pregnancy rate that could easily be chance (placebo 9% vs 12% vs 16% across groups, with wide, overlapping ranges of uncertainty) and no real improvement in sperm quality — in other words, no proven fertility benefit. Older, looser reports (for example, Guillon, 1975, which described a minority of 141 patients feeling subjectively better) had no comparison group, and the controlled trials above contradict them.

Depression / mood — no benefit over a dummy pill. A double-blind, placebo-controlled study of mesterolone in 52 depressed men (Itil et al., Methods Find Exp Clin Pharmacol 1984) found that symptoms improved no more than they did on placebo. Mesterolone also lowered testosterone levels. This fits the broader picture for using male hormones to treat depression — for example, a testosterone-replacement trial in depressed men with low testosterone (Seidman et al., J Clin Psychiatry 2001) found the antidepressant effect “could not be differentiated from” placebo.

Performance / “anti-estrogen” claims. There’s no strong human evidence for the SHBG-driven “free-testosterone,” “anti-estrogen,” or “hardening” effects that make it popular in physique circles.

The bottom line: for its two historic medical uses (fertility and mood), the controlled human evidence is negative or unconvincing, and there’s no credible human evidence behind the performance claims.

Legal and regulatory status

In the United States, mesterolone is a Schedule III controlled substance — classed as an anabolic steroid under the Anabolic Steroid Control Act/Controlled Substances Act — even though it was never sold or FDA-approved here (and isn’t approved in Canada either). Having it or distributing it without a prescription is a federal crime. For context on the drugs it usually gets grouped with: fluoxymesterone is also a Schedule III anabolic steroid; aromatase inhibitors (anastrozole, letrozole, exemestane) and SERMs (selective estrogen receptor modulators — drugs like tamoxifen, clomiphene, raloxifene that block or mimic estrogen in different tissues) are legitimate prescription medicines (not controlled substances) approved for cancer, hormone, and fertility uses, with any performance use being off-label; T3 (liothyronine) and insulin are prescription drugs (not controlled) approved for an underactive thyroid and diabetes respectively, with performance use being off-label and dangerous; and DNP (2,4-dinitrophenol) isn’t approved for people to take at all — the FDA called it “unfit for human consumption” after diet-pill poisonings in the 1930s, and it’s an industrial chemical sold illegally online as a “fat burner,” with deaths still happening today.

In sport, mesterolone is banned at all times — both in and out of competition — as an anabolic agent under WADA Class S1 on the 2026 Prohibited List. For comparison: aromatase inhibitors and anti-estrogens/SERMs fall under S4 (Hormone and Metabolic Modulators) — S4.1 covers aromatase inhibitors and S4.2 covers anti-estrogenic substances/SERMs; insulins and insulin-mimics fall under S4.4 (metabolic modulators); general metabolic modulators also sit under S4.4; and T3/thyroid hormone is not on the WADA Prohibited List.

Safety

Mesterolone carries the usual androgen-class harms, even though it avoids the obvious liver toxicity of the 17α-alkylated oral steroids.

• Androgenic effects: acne, oily skin, and faster male-pattern hair loss in men who are prone to it. In women it can cause virilization (developing male traits — a deeper voice, extra body hair, and clitoral enlargement) that is partly permanent.
• HPG-axis suppression: like other male hormones taken from outside the body, it quiets the hypothalamic-pituitary-gonadal axis (the brain-and-testicle hormone loop that controls natural testosterone), shutting down your own testosterone production.
• Cardiovascular / lipids: harmful shifts in blood fats (notably a drop in HDL, the “good” cholesterol), with possible effects on the heart and prostate from androgen exposure.
• Hepatotoxicity (liver harm): lower than with the 17α-alkylated oral steroids because it lacks that tweak — but that does not make it “safe.”
• Unregulated supply: black-market products aren’t quality-checked and are often mislabeled or contaminated.

Because mesterolone usually gets discussed alongside other, far more dangerous performance drugs, the honest harm picture for those companion drugs matters too:

• DNP (2,4-dinitrophenol): a mitochondrial uncoupler — it forces the body’s energy factories (mitochondria) to burn fuel as runaway heat instead of useful energy. That causes uncontrolled overheating and fatal hyperthermia (body temperatures reported as high as about 44 °C / 111 °F), a racing heart, dangerously acidic blood (metabolic acidosis), and cardiac arrest. There is no specific antidote — all doctors can do is treat the symptoms and cool the person aggressively — and overdoses are often fatal. DNP kills people. It is the most dangerous compound in this group.
• Insulin: misuse by people who aren’t diabetic can drop blood sugar to deadly levels — causing coma, permanent brain damage, and death, sometimes fast and with no warning.
• Aromatase inhibitors: driving estrogen too low harms bone density and worsens cholesterol and heart risk; joint pain and mood changes are common.
• SERMs (e.g., tamoxifen): raise the risk of dangerous blood clots (DVT/PE — clots in the legs or lungs), plus vision and liver effects.
• T3 (liothyronine): pushes the body into an overactive-thyroid state — a racing or irregular heartbeat, strain on the heart, bone loss, muscle breakdown, and shutdown of the body’s own thyroid system that may not bounce back quickly after stopping.

Bottom line

Mesterolone is an old, DHT-derived oral androgen that was sold abroad as Proviron for low testosterone and for male infertility with no clear cause — but it was never approved or sold in the United States. For its two historic uses, the controlled human trials are negative or unconvincing: a placebo-controlled fertility trial showed worse pregnancy rates than the dummy pill, a larger WHO study found no real fertility or sperm benefit, and a controlled depression study showed no benefit over placebo. Its bodybuilding reputation as an “anti-estrogen / free-testosterone” aid rests on its chemistry — it doesn’t convert to estrogen and it binds SHBG — rather than on credible human evidence. It’s a US Schedule III controlled substance, banned at all times in sport, and it carries the full androgen-class risk profile even though it sidesteps the liver toxicity of 17α-alkylated steroids. And among the drugs it tends to travel with, DNP and insulin are genuinely lethal.

Evidence grade: 1/10 · Unsupported.

Sources

• Mesterolone — Wikipedia (chemistry, 1α-methyl-DHT, non-aromatizing, high SHBG affinity, Schering/Proviron ~1967, never marketed in US, Schedule III)
• Mesterolone — DrugBank (DB13587)
• Gerris J et al. Placebo-controlled trial of high-dose mesterolone treatment of idiopathic male infertility. Fertil Steril. 1991 (PMID 1900485)
• WHO Task Force. Mesterolone and idiopathic male infertility: a double-blind study. Int J Androl. 1989 (PMID 2680994)
• Guillon G. Experience with mesterolone in male fertility disorders. Z Hautkr. 1975 (uncontrolled case series; PMID 1226948)
• Itil TM et al. The effects of mesterolone in depressed patients (double-blind controlled study). Methods Find Exp Clin Pharmacol. 1984 (PMID 6431212)
• Seidman SN et al. Testosterone replacement therapy for hypogonadal men with major depressive disorder: a randomized, placebo-controlled trial. J Clin Psychiatry. 2001 (PMID 11465516)
• WADA — The Prohibited List (2026; S1 anabolic agents; S4 hormone & metabolic modulators)
• 2,4-Dinitrophenol — Wikipedia (FDA “unfit for human consumption”; uncoupler; fatal hyperthermia; no antidote)
• Runaway uncoupling in 2,4-dinitrophenol poisoning: clinical and mitochondrial observations from two cases (PMC)
• Toxicological Profile for Dinitrophenols, Health Effects — NCBI Bookshelf (ATSDR)