Proviron
Mesterolone · Provironum · Vistimon · 1-methyl-DHT · 1α-methyl-4 · 5α-dihydrotestosterone
Last updated
At a glance
40
Testosterone = 100
150
Testosterone = 100
Overview
Why Proviron Has a Permanent Spot in the Cycle Spreadsheet#
Proviron (mesterolone) isn't a mass-builder and was never meant to be. It's the compound experienced users bolt onto a cycle to drop SHBG, raise free testosterone, soften estrogen, and rescue libido — the tuning knob that makes everything else on the stack work better. A 1α-methylated DHT derivative with negligible hepatotoxicity, it sidesteps the c17-alkylated liver load of Anadrol or Winstrol while delivering a pure, non-aromatizing androgenic signal.
The community has settled on three reasons to run it: hardening a cut (especially stacked with Masteron or Tren in the final weeks before a photo), restoring drive and erectile quality on cycles where an AI has over-suppressed E2 or where 19-nors like Deca have blunted libido, and optimizing free T on TRT by displacing testosterone from SHBG.
"The sex hormone-binding globulin of human blood plasma binds mesterolone with higher affinity than testosterone itself, suggesting a capability to displace testosterone and estradiol from SHBG." — Saartok et al., Endocrinology (1984)
That SHBG mechanism is why 25–50 mg/day can noticeably shift how your existing testosterone feels without changing your weekly dose at all. Below, this guide covers the full dosing ladder, how Proviron fits into cut / cruise / 19-nor rescue stacks, half-life and AM/PM split logic, the side-effect profile (including why finasteride won't save your hairline here), and why it's a terrible choice for PCT despite persistent forum folklore.
How Proviron works
Mesterolone is a 1α-methylated dihydrotestosterone derivative — structurally a pure androgen, functionally a tuning compound the physique community uses to free up testosterone, harden a look, and rescue libido. It doesn't build tissue directly in any meaningful way (anabolic rating ~40, androgenic ~150). What it does is rearrange the hormonal environment around the testosterone you're already running so more of it actually works.
Four mechanisms drive the real-world effects.
SHBG Displacement and Free Testosterone Elevation#
The headline mechanism. Mesterolone binds sex hormone-binding globulin with unusually high affinity — higher than testosterone itself — physically displacing bound T and estradiol off the carrier protein and into the free, bioavailable pool. This is why 25–50 mg/day can produce a noticeable "more on the same dose" effect on TRT or cruise without touching the testosterone ester.
"The sex hormone-binding globulin of human blood plasma binds mesterolone with higher affinity than testosterone itself, suggesting a capability to displace testosterone and estradiol from SHBG." — Saartok T, Dahlberg E, Gustafsson JÅ. Endocrinology, 1984
Practical outcome: higher free T, better libido, better erection quality, better subjective well-being — typically visible on bloodwork within 2–4 weeks, with SHBG dropping measurably. For high-SHBG guys on TRT whose total T looks fine but whose free T is still symptomatic, this is the entire pitch.
Direct Androgen Receptor Agonism in DHT-Sensitive Tissue#
Mesterolone is a strong AR ligand with a classic DHT profile — it lights up receptors in skin, scalp, prostate, CNS, and the reproductive tract rather than driving hypertrophy in skeletal muscle. This is where the "hardening" aesthetic, aggression, libido drive, and confidence come from on a cut. It also explains the downside column: acne, sebum, androgenetic hair loss, prostate growth.
"Among widely used AAS, mesterolone is noteworthy for minimal hepatotoxicity, but like other DHT derivatives, presents dose-dependent androgenic side effects including acne and hair loss." — Skrzypiec-Spring M, et al. Journal of Clinical Medicine, 2024
Because the molecule is DHT (with a 1α-methyl on the A-ring), oral 5α-reductase inhibitors like finasteride and dutasteride do not block its action at the scalp or prostate. Hair-vulnerable users running Proviron need topical AR antagonists — RU58841 or pyrilutamide — at the follicle itself. Finasteride is the wrong tool for this compound.
Weak Competitive Aromatase Inhibition#
Mesterolone occupies the aromatase enzyme without being a viable substrate, producing a modest tissue-level anti-estrogen effect. It's not an AI replacement — don't drop anastrozole on a heavy test cycle and expect Proviron to hold E2 — but on a moderate test-only run (250–500 mg/week), 50 mg/day often covers the estrogen gap without the crash risk of dosing a real AI. This is also why stacking Proviron on top of a properly dosed AI is how people accidentally flatten estrogen and kill the libido they were trying to protect.
No Aromatization, No Further 5α-Reduction#
Because mesterolone is already 5α-reduced, it is a metabolic dead end for both aromatase and 5α-reductase. It cannot convert to estrogen, and it cannot be amplified into a stronger androgen the way testosterone becomes DHT in target tissues. What you dose is what acts. This gives the "clean DHT" profile the community values — no water, no estrogenic sides, no gyno risk, no nipple sensitivity — and is the reason it slots so cleanly into pre-contest and hardening protocols.
1α-Methyl Oral Activity Without Hepatotoxicity#
Unmodified DHT is orally inactive — it gets chewed up by hepatic 3α-hydroxysteroid dehydrogenase before it can act systemically. Mesterolone's 1α-methyl group blocks that degradation pathway, making the molecule orally bioavailable without resorting to 17α-alkylation.
"Mesterolone is rendered orally active by the introduction of a 1-alpha methyl group, which is sufficient to protect the molecule from rapid hepatic degradation typical for DHT-type androgens." — Nieschlag E, Behre HM (eds), Testosterone: Action, Deficiency, Substitution, 4th ed., 2012
Practical outcome: you get an oral androgen that doesn't behave like an oral in the way that matters — liver values stay clean, no cholestatic pattern, no need for TUDCA or NAC at reasonable doses, and cycle length can extend to 12–16 weeks without the hepatic ceiling that limits Anadrol or Dianabol to 4–6 weeks. This is the single feature that makes Proviron practical as a year-round TRT adjunct rather than a time-limited cycle drug.
Protocol
| Level | Dose | Frequency | Notes |
|---|---|---|---|
| Low | 25–25 mg | Twice daily | Documented entry-level range |
| Mid | 50–50 mg | Twice daily | Most commonly studied range |
| High | 75–100 mg | Twice daily | Split AM/PM with meals due to ~12 h half-life. Three-times-daily dosing at 75–100 mg/day keeps serum levels steadier. |
Cycle length & outcomes
Documented cycle
8–16 weeks
Plateau after
12 wks
Cycle Structure#
Proviron isn't a compound you "cycle" in the traditional sense — it's a tuning tool bolted onto a testosterone base, a cruise, or a TRT protocol. There's no loading phase, no taper, and no hepatic clock forcing you off. The 1α-methyl substitution dodges the c17-alkylated hepatotoxicity problem entirely, which is why run lengths are dictated by the underlying cycle, not by the mesterolone itself.
"Mesterolone is rendered orally active by the introduction of a 1-alpha methyl group, which is sufficient to protect the molecule from rapid hepatic degradation typical for DHT-type androgens." — Nieschlag & Behre, Testosterone: Action, Deficiency, Substitution, 4th ed. (2012)
Dose Ladder by Goal#
| Goal | Cycle Length | Daily Dose | Split |
|---|---|---|---|
| TRT free-T optimizer (SHBG drop) | 8–16 weeks or continuous | 25 mg | Single AM dose |
| On-cycle libido / erectile rescue | Run for duration of AAS cycle | 25–50 mg | AM / PM |
| Cut hardening (final phase) | Last 6–10 weeks pre-peak | 50 mg | AM / PM |
| 19-nor rescue (Deca/NPP stacks) | Full duration of nandrolone run | 50 mg | AM / PM |
| Advanced / pre-contest finisher | 8–12 weeks | 75–100 mg | 3× daily with meals |
The 50 mg/day split is the community consensus sweet spot — enough SHBG displacement and androgenic tone to see and feel, without the DHT sides climbing into problem territory.
"Most users find 50mg split AM and PM to be the sweet spot — excellent for hardening, libido, and keeping SHBG down without excessive androgenic sides." — r/steroids community guide (2016)
Dosing Frequency & Timing#
With a ~12–13 hour half-life, once-daily dosing creates a real peak-trough swing. Split AM/PM at 50 mg/day, or three times daily with meals at 75–100 mg/day, to keep serum levels stable. Take with food — mesterolone is lipophilic and absorption is better with a meal containing fat.
There's no benefit to pre-workout timing specifically; steady-state serum levels are what drive the effect, not an acute spike.
Onset Timing — What to Expect#
- Days 3–7: Libido and morning erections pick up noticeably. This is the fastest, most reliable subjective marker that the product is real and dosed correctly.
- Weeks 2–4: SHBG drops measurably on bloodwork; free T rises from the same weekly test dose. Skin looks slightly tighter, physique feels denser.
- Weeks 4–8: Hardening and aesthetic effect peaks. At low body fat, this is where Proviron earns its reputation as a finisher.
- Week 8+: Plateau. AR saturation means pushing past 100 mg/day yields more sides than benefits.
If morning wood and SHBG haven't moved by week 3 on 50 mg/day, the product is underdosed — Proviron is one of the most counterfeited orals on the underground market, and bloodwork is the only way to know.
Bloodwork Cadence#
Run a baseline panel before starting, mid-cycle at 6–8 weeks, and end-of-cycle. The core markers:
- Total T, Free T, SHBG — the SHBG drop is the objective confirmation the compound is working. Expect a meaningful fall within 2–4 weeks on 50 mg/day.
- E2 sensitive — mesterolone's weak aromatase inhibition will nudge E2 down; don't crash it by stacking a full AI dose on top.
- Hematocrit — additive erythrocytosis risk on a test base.
- Lipids — modest HDL hit, milder than alkylated orals but real.
- PSA — relevant for users 35+ or with prostate history.
- LH/FSH — if you care about keeping your axis awake on a cruise; mesterolone becomes clearly suppressive at 75–100 mg/day.
PCT Considerations#
Proviron is not PCT. Despite decades of forum folklore, mesterolone is suppressive at physique doses and has no LH-restoring action. Run your standard SERM-based PCT (clomid/nolva) driven by the underlying cycle, not by the Proviron.
"Although mesterolone was initially developed to treat male infertility, its suppressive effects at higher doses can paradoxically diminish spermatogenesis." — Jung & Seo, Clin Exp Reprod Med (2014)
Tapering & Discontinuation#
No taper required. Because Proviron doesn't suppress the HPTA meaningfully at 25–50 mg/day and carries no hepatic rebound, you can stop abruptly at the end of the cycle. The SHBG will drift back up over 2–3 weeks and libido will settle to whatever the underlying testosterone level supports. That's it — no crash, no rebound estrogen surge, no liver recovery window.
Body Transformation Preview
Lean Mass Gain
1.4 lbs
1.0–1.7 lbs range
Fat Loss
0.0 lbs
0.0–0.0 lbs range
Lean Gain by Week
Risks & mistakes
Common (most users)#
- Increased libido / spontaneous erections — usually welcome, but can be disruptive at 75–100 mg/day. Drop to 50 mg if it's interfering with sleep or daily life.
- Oily skin and mild acne — classic DHT signature. Manage with a salicylic acid wash, benzoyl peroxide on the back/shoulders, and a retinoid if you're already acne-prone.
- Accelerated scalp hair shedding (in predisposed users) — mesterolone IS DHT, so oral finasteride/dutasteride will NOT protect the scalp. Topical AR antagonists (RU58841, pyrilutamide) plus minoxidil are the only real mitigation while running it.
- Increased body/facial hair growth — cosmetic, not a health issue; dose-dependent.
- Mild sleep disruption / wakefulness — take the PM dose with dinner rather than right before bed.
- Subjective aggression / drive increase — mostly positive, but watch for short fuse at 75 mg+.
"Most users find 50 mg split AM and PM to be the sweet spot — excellent for hardening, libido, and keeping SHBG down without excessive androgenic sides." — r/steroids community guide (2016)
Uncommon (dose-dependent or individual)#
- Hematocrit creep — additive with any testosterone base. Check CBC at 6–8 weeks; donate blood or reduce dose if HCT climbs past ~52%.
- Negative lipid shift (HDL↓, LDL↑) — milder than c17-alkylated orals but real. Pull a lipid panel mid-cycle; add cardio, fish oil, and consider citrus bergamot if HDL falls off a cliff.
- Estrogen crash symptoms — dry joints, flat mood, dead libido — when stacked with an AI on a moderate cycle. If this happens, drop the AI first, not the Proviron; the whole point of adding mesterolone was to avoid needing the AI.
- HPTA suppression — mild at 25 mg, clearly suppressive at 75–100 mg/day. Mesterolone is not a PCT drug despite old forum folklore.
- Suppressed spermatogenesis at physique doses — paradoxical given its off-label fertility use at low clinical doses.
"Although mesterolone was initially developed to treat male infertility, its suppressive effects at higher doses can paradoxically diminish spermatogenesis." — Jung & Seo, Clin Exp Reprod Med (2014)
- PSA elevation / mild prostate enlargement — minor at standard doses in young users; monitor with a PSA draw if you're 40+ or have any BPH history.
- Irritability / anxiety — uncommon but reported above 75 mg/day. Back off to 50 mg.
Rare but serious#
- Clinically significant polycythemia (HCT >54%) — warning signs are headaches, facial flushing, visual disturbances, ringing ears. Stop, donate blood, and re-test before resuming.
- Prostate pathology — difficulty urinating, weak stream, nocturia, or a rising PSA trend. Stop and get evaluated.
- Hepatic strain — genuinely rare with mesterolone. If you see RUQ pain, jaundice, or dark urine, stop immediately and pull an LFT panel, though this is almost always a sign the "Proviron" was actually something else (counterfeit / mislabeled oral).
"Among widely used AAS, mesterolone is noteworthy for minimal hepatotoxicity, but like other DHT derivatives, presents dose-dependent androgenic side effects including acne and hair loss." — Skrzypiec-Spring et al., J Clin Med (2024)
Hard contraindications#
- Prostate cancer, active or in remission — mesterolone is a strong AR agonist; do not use.
- Existing or prior hepatic tumors — rare class-level risk for all AAS.
- Women — strongly virilizing (voice deepening, clitoral hypertrophy, hirsutism) with no legitimate female use case. Do not use.
- Pregnancy or potential pregnancy in a partner exposed to the tablets — androgenic, teratogenic potential to a female fetus.
- Men actively trying to conceive in the next 3–6 months — suppresses spermatogenesis at 50 mg+ daily.
- Untreated polycythemia (baseline HCT already >52%) — address first, then reassess.
- Untreated hypertension or severe dyslipidemia — get these in range before adding any oral androgen to a cycle.
Gender and PCT considerations#
Women: Do not use. The anabolic:androgenic ratio (~40:150) is virtually all androgenic, and virilization risk is higher than with anavar or primobolan at any meaningful dose.
Fertility: If conception is on the roadmap, run mesterolone out and allow 3+ months of washout with the rest of the cycle before attempting. The low-dose clinical fertility protocols (25 mg) are a different tool used for a different endpoint and don't translate to bodybuilding dosing.
PCT: Mesterolone is not a PCT compound — it is suppressive, not restorative, and will actively interfere with HPTA recovery. Standard SERM-based PCT (nolvadex / clomid) is driven by the testosterone base of the cycle, not by the Proviron. Drop the mesterolone when you drop the test, then run PCT as normal.
Stack & combine
Multipliers applied when these compounds run together. Values > 1 indicate a bonus on that axis. Tap a partner to expand the mechanism.
| Partner | Type | Lean | Fat loss | Recovery |
|---|---|---|---|---|
| synergistic | ×1.08 | ×1.03 | ×1.15 | |
| synergistic | ×1.05 | ×1.02 | ×1.12 |
FAQ — Proviron
Research & citations
5 studies cited on this page.
Conclusion
Proviron is a nearly side-effect-free way to sharpen a cycle, boost free testosterone, and rescue libido without risking your liver or crashing your estrogen.
Key takeaways:
- Standard dose: 25–50 mg/day (split AM/PM) is effective for SHBG drop, hardening, and libido; advanced users reach 75–100 mg/day if hair and prostate aren't concerns
- Oral route, 12–13 hour half-life; split dosing keeps blood levels steady
- Cycle length: 8–16 weeks typical; can be run year-round at 25 mg/day with TRT
- Best stacked as an add-on — not a mass builder, but the gold-standard free-T and 'libido rescue' ancillary for test cycles, cutting stacks, and 19-nor protocols
- No PCT required for short/low doses, but avoid for anyone managing fertility, hair loss, or at risk of prostate issues
- Side effects: manageable androgenic (acne, hair loss, mild HDL drop), negligible hepatotoxicity
If you want your test to hit harder, look drier on stage, or fix cycle-induced libido issues, Proviron is one of the most community-tested ancillaries in the kit — just run proper bloodwork to confirm your source and results.