RU58841
PSK-3841
RU58841 (PSK-3841) is a hormonal & sexual research compound. Non-steroidal androgen receptor antagonist designed for topical use — it blocks DHT AT the follicle rather than lowering it systemically, which is the entire appeal versus finasteride.
RU58841 quick facts
| Reported research dose | 50mg/mL topical, 0.5–1mL to the scalp daily (research) |
| Route | Topical |
| Frequency | 1x at night |
| Half-life | Intended to be locally acting; systemic absorption in humans is not well characterized |
| Forms | Topical |
| Evidence level | Animal and anecdotal only. No human trial has ever been published |
Extremely popular in hair-loss communities and genuinely under-evidenced. It was abandoned in development and no human safety data exists — the claim that it stays local is a design intention, not a demonstrated fact, and there are anecdotal reports of systemic suppression. This entry exists because people are using it and deserve an honest read, not because I'd recommend it.
How RU58841 works
Non-steroidal androgen receptor antagonist designed for topical use — it blocks DHT AT the follicle rather than lowering it systemically, which is the entire appeal versus finasteride.
Proposed benefits
Researched for libido, hormonal signaling and reproductive / sexual function.
Where to get RU58841
Buy RU58841 at Disguised Alpha →The evidence for RU58841
Graded by what exists behind each claim.
Human clinical evidence
- No human trials: development stopped at preclinical, so the ceiling on any claim here is a rodent model — and these transfer poorly.
📊 Correlative data
- Developed for androgenetic alopecia and abandoned before human trials — not for a published safety finding, but the program ended and no data was released, which is itself worth weighing.
- Community use is substantial and long-running, with reports of efficacy comparable to or better than topical finasteride and, in some users, systemic effects that the 'non-systemic' framing does not predict. Beyond that the record is self-reported: community dosing logs are real information about tolerability and almost none about efficacy.
🧪 How the mechanism reads
- A non-steroidal androgen receptor antagonist designed for topical use — it blocks the receptor locally rather than reducing DHT, which is a different mechanism from finasteride entirely.
- The design intent was local action with rapid systemic breakdown. Whether that holds at real-world doses is the unanswered question, and reports of systemic androgen blockade suggest it may not always.
Why an empty tier is not a verdict → · What community dosing logs are worth →
How to read these tiers: they say how much human evidence exists, not how well something works — and ✗ flags harm, never a disappointing trial. How the evidence tiers work →
What RU58841 actually does
Start with what this molecule is, because the structure explains both the design intent and why the design intent is only half-proven. RU58841 is 4-[3-(4-hydroxybutyl)-4,4-dimethyl-2,5-dioxoimidazolidin-1-yl]-2-(trifluoromethyl)benzonitrile, C17H18F3N3O3, molecular weight 369.34, computed XLogP 2.1 National Center for Biotechnology Information 2026. Two halves matter.
The first half is a 4-cyano-3-(trifluoromethyl)phenyl group fused to a dimethylhydantoin. That is not a novel pharmacophore — it is the same benzonitrile-hydantoin architecture that defines the non-steroidal antiandrogen class, and it is why RU58841 is an androgen receptor antagonist and not a 5-alpha-reductase inhibitor. This distinction is the single most important thing on the page. Finasteride and dutasteride reduce how much DHT gets made. RU58841 lets DHT be made and stops it binding. Circulating DHT is therefore unchanged on this compound, which means every bloodwork intuition carried over from finasteride is wrong here.
The second half is the 4-hydroxybutyl chain hanging off the hydantoin nitrogen — a polar handle no other antiandrogen in the class carries. It is a deliberate metabolic soft spot: a primary alcohol is an easy target for oxidation and for conjugation, which is the standard way a medicinal chemist builds a soft drug, one designed to work where it is applied and be dismantled once it reaches the circulation. Combined with a molecular weight under 400 and an XLogP of 2.1 — close to the optimum for crossing the stratum corneum — this is a molecule engineered end to end for topical androgen blockade National Center for Biotechnology Information 2026.
The receptor pharmacology has been measured, and it is not weak. Battmann 1994 reports high affinity for hamster prostate and flank organ androgen receptors. Pan 1998 went further, cotransfecting human prostate cancer PC3 cells with wild-type androgen receptor and an androgen-responsive MMTV-ARE-CAT reporter: across 10−11 to 10−7 M, RU58841 showed no agonist activity at all — it never activated the receptor — and it competitively suppressed DHT activation of the receptor with a potency comparable to hydroxyflutamide, the active metabolite of flutamide.
Sit with that last comparison, because the paper's own authors did. Hydroxyflutamide is a systemically active antiandrogen used to treat prostate cancer. A molecule of equal receptor potency does not become safe by being applied to skin; it becomes safe only if it does not reach the circulation in an active form. Pan 1998 draws exactly that inference in print — that topical RU58841 may induce systemic side effects — in the same abstract that reports its topical success in macaques. The molecule's potency and its safety argument are in tension, and that tension is the honest summary of this compound.
Cell, rodent, human — and where it stops
This is the whole evidence chain. Four papers. There is no fifth, and there is no human trial.
Step one, hamster flank organ. Battmann 1994 applied RU58841 topically to the androgen-dependent flank organ of hamsters and got dose-dependent regression at a dose as low as 1 µg per animal, with no antiandrogenic activity on the deep accessory sex organs and no effect on testosterone up to 100 µg per animal. Then the comparison that quantifies the entire “stays local” claim: given subcutaneously, it took 300 µg per animal to produce a flank organ reduction equivalent to 1 µg applied topically, along with weak systemic activity. That is a roughly 300-fold local-to-systemic advantage — a real, measured number, and it is the strongest single piece of evidence this compound has. It was measured in a hamster.
Step two, hamster ear sebaceous glands, and this one contains two findings nobody quotes. Matias 1995 applied RU58841, RU56187, RU38882 and cyproterone acetate topically for four weeks to the ventral ear pinna of sexually mature male Syrian hamsters. RU58841 was the most effective of the four, producing a maximal 60% reduction in sebaceous gland size at 10 µg per day, with no inhibition on the contralateral untreated ear — direct evidence of local containment in that model. Now the two overlooked results. Extending treatment from 4 weeks to 12 weeks produced no greater inhibition. And the effect was fully reversible: the glands returned to normal size within 4 weeks of stopping. A plateau at one month and complete reversal in one month is the actual shape of this drug's action, and it is not the shape most users assume.
Step three, human tissue — on a mouse. De Brouwer 1997 used the closest thing to a human experiment that exists: 20 productive scalp grafts taken from balding men and maintained on female nude mice conditioned with topical testosterone propionate, 300 µg in 10 µL, five days a week, on the non-grafted flank. Grafts were split by estimated hair production potential and randomized to blinded RU58841 1% in ethanol or ethanol alone, applied five days a week, with hair production followed monthly for six months. The control grafts bore 28 active follicles, of which 2 (7%) started a second hair cycle. The RU58841 grafts bore 29 active follicles, of which 8 (28%) did, and linear hair growth rates were significantly higher (p < 0.04). The authors' closing sentence is that this encourages a clinical trial.
Step four, macaque. Pan 1998 reports that in the stump-tailed macaque model of androgenetic alopecia, topical RU58841 produced a potent increase in hair density, thickness and length, with no systemic effects detected — while the same paper's cell work showed receptor potency comparable to hydroxyflutamide and warned that systemic effects were possible.
The obstacle, and it is not subtle: the clinical trial De Brouwer 1997 called for in 1997 was never published. Twenty-nine years later there is no phase 1, no phase 2, no published human pharmacokinetics, no human safety database and no human efficacy data of any kind. Two further obstacles sit underneath that. The unit of analysis in the best study was a graft, not a person — ten grafts per arm, with the follicle as the counted event. And every containment result comes from an animal whose skin is not human skin: hamster ear and mouse flank differ from human scalp in thickness, follicle density and blood supply, and percutaneous absorption scales with all three. The 300-fold margin Battmann 1994 is a hamster number, and nobody has ever measured the human one.
RU58841 pharmacokinetics — how much of it actually gets in
There is no human pharmacokinetic study of this compound. None. So this section is arithmetic and inference, and it is labeled as such.
Route: topical, and there is no other. No injectable form exists and no oral form is used; there is no published oral bioavailability figure, no measured first-pass extraction and no identified clearing enzyme. What can be said about degradation is structural rather than measured: the 4-hydroxybutyl chain is the designed soft spot National Center for Biotechnology Information 2026, and a primary alcohol on a small lipophilic molecule is normally handled by oxidation via alcohol dehydrogenase or a cytochrome P450, followed by glucuronidation — but no published study names which cytochrome or which esterase does it in a human, and no metabolite has been identified in human plasma. The label statement “systemic absorption in humans is not well characterized” is literally true and is the only honest thing that can be written.
The one exposure comparison that exists, and it is a hamster. Battmann 1994 needed 300 µg subcutaneously to match what 1 µg topically achieved locally. Take that ratio at face value and a scalp dose in the milligram range would need to deliver less than about 0.3% of itself systemically to stay below a pharmacologically active blood concentration. Whether human scalp does that has never been measured.
Do the arithmetic on a real-world dose, because it is sobering. A common research preparation is 50 mg/mL with 0.5–1 mL applied daily — that is 25 to 50 mg per day onto the scalp. Compare with the doses at which every efficacy result in this compound's literature was generated: 1 to 10 µg per animal per day Battmann 1994 Matias 1995, and a 1% solution on a graft De Brouwer 1997. Human use is running three to four orders of magnitude above the milligram-per-day figures in the animal work, on a much larger surface area, with an unmeasured absorption fraction. Even a 1% systemic absorption fraction from 50 mg is 500 µg per day reaching the blood — of a molecule with hydroxyflutamide-level receptor potency Pan 1998. That single calculation is the reason the “it stays local” claim cannot be assumed, and it is why the bloodwork in the next section is not optional.
Onset and offset can be bounded, though. Matias 1995 reports the local effect plateauing by 4 weeks with no further gain out to 12, and complete reversal within 4 weeks of stopping. If human follicles behave like hamster sebaceous glands, that predicts a roughly one-month onset, a ceiling, and a one-month washout — a shorter commitment than finasteride and vastly shorter than dutasteride's five-week half-life.
What would have to be true, and how you would know it was not
The whole point of this compound is a claim about where it acts, and that claim is directly testable with a standard blood panel. Almost nobody using it runs one, which is why the anecdotal record is an argument instead of a dataset.
1. DHT should not move. If it does, something is wrong with your product. This is a receptor antagonist, not a 5-alpha-reductase inhibitor Pan 1998. Draw Total & Free DHT at baseline and at 8 weeks. Prediction: unchanged. A large fall in DHT means you are not taking what the label says — the most likely explanation is a product adulterated with, or substituted by, finasteride or dutasteride, which is a real problem in an unregulated supply chain.
2. The decisive test is LH, and it is decisive because the mechanism forces it. Androgen receptors in the hypothalamus and pituitary mediate testosterone's negative feedback. A systemically present AR antagonist blocks that feedback, so LH & FSH rise and Total Testosterone follows — this is exactly what flutamide and bicalutamide do, and RU58841's receptor potency is comparable to hydroxyflutamide's Pan 1998. Draw LH, FSH and total testosterone at baseline and again at 8–12 weeks of consistent use. If the compound is genuinely staying local, all three are flat. If LH and testosterone have climbed, the drug is in your circulation and is occupying receptors in your brain. There is no third interpretation. Add SHBG to the same draw as a secondary signal of changed hepatic androgen and estrogen tone.
3. The prediction that cuts against it: the effect should stop improving after about a month, and should be gone about a month after you stop. Matias 1995 found no additional inhibition between week 4 and week 12, and full reversal within 4 weeks of cessation. So standardized scalp photography at baseline, 4, 12 and 24 weeks should show most of whatever is going to happen arriving early and then flattening. If somebody reports steadily accelerating gains at month six, the mechanism as characterized does not predict it, and the likeliest explanations are the minoxidil it is usually dissolved with, concurrent finasteride, or the ordinary regression-to-the-mean of a condition that fluctuates.
4. And the negative control nobody runs. Apply vehicle only to a defined patch for eight weeks alongside treated scalp. Every positive result in this compound's literature came from a study with a vehicle control Matias 1995 De Brouwer 1997; the entire human record has none.
What nobody has tested yet
Nobody has ever measured RU58841 in human blood. Not once, not in any published study. It is a small molecule with an established structure National Center for Biotechnology Information 2026; an LC-MS/MS assay is routine analytical chemistry. Ten people applying their usual dose, with plasma sampled at 0, 2, 4, 8 and 24 hours, would produce the single most valuable missing number attached to this compound — and would either confirm the soft-drug design or end the argument permanently. It has never been done, which is remarkable given how many people are applying it nightly.
Nobody has published the reason the program stopped, and the distinction matters. Development ending is not the same as a toxicity finding, and this page will not pretend otherwise. Programs stop for portfolio reasons, patent timing, formulation problems and corporate reorganization at least as often as for safety. What is true is narrower and worse: no safety data was ever generated in humans, so no safety data was ever withheld. The absence of a published harm is not evidence of absence of harm; it is evidence that nobody looked. Anyone citing the abandonment as proof of danger, and anyone citing it as proof of nothing, are both overreading it.
Nobody has run the human dose-response. Every dose in the literature is an animal dose — 1 to 10 µg per animal Battmann 1994 Matias 1995 — or a concentration on a graft De Brouwer 1997. The 50 mg/mL preparations in circulation were not derived from any of it. A four-arm study at 0.5%, 2.5%, 5% and vehicle on standardized scalp photography, with plasma sampling built in, would establish both the effective concentration and the systemic cost, and it is exactly the trial De Brouwer 1997 asked for in 1997.
And nobody has compared it head to head with topical finasteride, the only other locally-acting antiandrogen strategy for the same problem, despite the two being routinely discussed as alternatives.
RU58841 — its own safety story, not its class's
The honest headline: there is no human safety data for this compound at all. Zero published trials, zero published pharmacokinetics, zero adverse event tables, zero long-term follow-up. Everything below is either an animal finding or a mechanism-based prediction, and it is labeled which.
What the animal work actually showed about containment. Matias 1995 found no inhibition of the untreated contralateral ear, and Battmann 1994 found no effect on deep accessory sex organs and no change in testosterone up to 100 µg per animal. Those are genuine negative findings and they are the best evidence the compound has. They were obtained at microgram doses in rodents. They do not transfer automatically to 25–50 mg per day on a human scalp, and no study has tested whether they do.
The predicted risk, stated from mechanism. If enough drug reaches the circulation, RU58841 does what any systemic androgen receptor antagonist does: blocks hypothalamic feedback, raising LH and testosterone; blocks receptors in muscle, bone, libido pathways and breast tissue. The predicted picture is reduced libido, erectile difficulty, low mood and gynecomastia — and note that the gynecomastia route here differs from the aromatase-inhibitor conversation, because unopposed estrogen signaling in breast tissue with androgen signaling blocked is precisely how flutamide and bicalutamide cause it. Community reports of systemic effects are consistent with this mechanism rather than surprising under it.
The liver question, which nobody discusses and should. Non-steroidal antiandrogens sharing this pharmacophore have a documented class history of hepatotoxicity — flutamide's is severe enough to carry a boxed warning in its own right. Whether RU58841 shares it is unknown: nobody has published a liver panel from anybody taking it. A baseline and 12-week Comprehensive Metabolic Panel costs almost nothing and is the only liver surveillance available for a compound with no monitoring guidance because it has no approval.
Sourcing is a safety issue here in a way it is not for an approved drug. There is no pharmacopeial standard for RU58841, no regulatory inspection of who makes it, and no assay on a vial to verify. The specific failure mode to watch for is a product that lowers DHT — which this molecule cannot do — because that indicates a 5-alpha-reductase inhibitor in the bottle, taken by somebody who chose this compound explicitly to avoid one.
What the abandonment does and does not mean, one more time. It means no regulator has assessed this molecule, no manufacturing standard applies, no dose was ever established in a person, and no adverse event reporting system exists. It does not mean a hidden toxicity was found and buried. Both halves of that sentence are load-bearing, and this page exists because people are using the compound and deserve the accurate version rather than either scare story.
Sources read for this page
- Battmann T, Bonfils A, Branche C. RU 58841, a new specific topical antiandrogen: a candidate of choice for the treatment of acne, androgenetic alopecia and hirsutism.. J Steroid Biochem Mol Biol 1994 · PMID 8136306
- Matias JR, Gaillard M. Local inhibition of sebaceous gland growth by topically applied RU 58841.. Ann N Y Acad Sci 1995 · PMID 7625751
- De Brouwer B, Tételin C, Leroy T. A controlled study of the effects of RU58841, a non-steroidal antiandrogen, on human hair production by balding scalp grafts maintained on testosterone-conditioned nude mice.. Br J Dermatol 1997 · PMID 9415227
- Pan HJ, Wilding G, Uno H. Evaluation of RU58841 as an anti-androgen in prostate PC3 cells and a topical anti-alopecia agent in the bald scalp of stumptailed macaques.. Endocrine 1998 · PMID 9798729
- National Center for Biotechnology Information. PubChem Compound Summary for CID 132981, RU-58841.. PubChem, retrieved 2026
RU58841 — safety, predicted from mechanism
Predicted from mechanism, not from a human safety trial. How that reasoning works →
What the mechanism predicts
Derived from the molecule, not a trial.
- These block 5-alpha-reductase, the enzyme converting testosterone to DHT. That is the point — DHT drives androgenetic hair loss and prostate growth — and it is also the mechanism behind every predicted problem, because DHT is not only a hair hormone.
- DHT contributes to libido, erectile function and mood. Suppressing it systemically predicts reduced libido, erectile difficulty and mood changes in a minority of users.
- Topical formulations (RU58841, topical finasteride) exist specifically to reduce systemic exposure. They are not exposure-free — measurable systemic absorption happens — but the argument for them is a real one rather than marketing.
What has actually been reported
- Sexual side effects are on the label and reported in trials at low single-digit percentages, typically resolving on discontinuation.
- Post-finasteride syndrome — persistent symptoms after stopping — is reported by a subset of users and remains genuinely contested. Its mechanism is not established, and dismissing it and asserting it are both overstating what is known.
- Finasteride and dutasteride roughly HALVE PSA. A 'normal' PSA of 2.0 on finasteride is effectively 4.0.
How to reduce the risk
Same mechanism as the prediction.
- Get a baseline PSA before starting, or a later reading has nothing to be compared against and the halving effect hides a real rise.
- Start topical rather than oral if the concern is systemic exposure. Dutasteride inhibits both isoenzymes and has a much longer half-life than finasteride — it is the harder one to reverse quickly.
- Stop at the first sign of persistent sexual or mood change rather than waiting to see whether it settles.
What it does to your bloodwork
A fact about the assay.
- PSA before starting and periodically after — and remember to double the reading for interpretation. Total testosterone, DHT if you want to confirm the drug is doing what you think.
Don't run this if
- You are or may become pregnant, or you are a woman of childbearing potential — these are teratogenic and the risk is to a male fetus. Do not handle crushed or broken tablets.
- You are actively trying to conceive; effects on semen parameters are documented.
The honest unknown
- Whether persistent post-treatment symptoms represent a distinct syndrome, and who is susceptible, is unresolved.
Not medical advice. If you take prescription medication or have a diagnosed condition, check this with a pharmacist or doctor.
RU58841 — interference & stacking
Predicted from mechanism, not from an interaction study. How mechanism-predicted claims are made →
What RU58841 moves on your bloodwork
Expected direction, not a measured one.
- Complete Blood Count (CBC) with Differential — ↑ expected to rise
Hematocrit and hemoglobin rise — androgens stimulate erythropoiesis. This is the most reliably predictable movement of any compound in the Vault.
What to do: This is the number that decides whether you keep going. Baseline and every 3 months. Dehydration on the draw day inflates it, so hydrate normally or you will chase a false reading. - Total Testosterone — ↑ expected to rise
Expected. Trough vs peak matters enormously — the same protocol reads completely differently depending on when you drew.
What to do: Draw at the same point in the cycle every time or the trend is noise. - LH & FSH — ↓ expected to fall
Suppressed by negative feedback. This is the mechanism, not a side effect — and it is why exogenous androgen shuts down your own production.
What to do: Relevant if fertility matters to you. Worth knowing before, not after. - Estradiol, Sensitive (LC/MS-MS) — ↑ expected to rise
Aromatization converts a fraction to estradiol, and it rises with the androgen. Use the sensitive (LC-MS/MS) assay — the standard immunoassay is unreliable in men and produces numbers people then medicate.
What to do: If you are reading estradiol in a man, the assay choice matters more than the result. - SHBG (Sex Hormone-Binding Globulin) — ↓ expected to fall
Falls with androgen exposure, which raises the free fraction — so free testosterone can climb faster than total.
What to do: Read total and SHBG together; total alone understates what changed. - Lipid Panel (Cholesterol, HDL, LDL, Triglycerides) — ↓ expected to worsen
HDL falls, sometimes markedly. Oral 17-alpha-alkylated compounds do this far more aggressively than injectable esters.
What to do: Baseline and 12 weeks. ApoB is the better long-term read than LDL-C. - PSA (Total + Free + % Free) — ↑ expected to rise
Androgens can raise PSA modestly. It does not create prostate cancer that wasn't there, but it can unmask it.
What to do: Baseline before starting matters — without it, a later number has nothing to be compared against.
- How to work up to it, and when not to
- When to take it, and why that window
- Cycle length
- Time off between cycles
- Fasted or fed, and when in the day
- Coach Cam's personal notes
- Which compounds push the same lever, and why the dose adds up faster than people count
- What blunts it — the stacks that waste your money
- What compounds the risk, so a side effect arrives sooner than any one of them suggests
- Coach Cam's read on running it alongside the rest of your protocol
Everything above is free and stays free. Skool is where it becomes a plan — RU58841 in an order, with the rest of what you're running.
Unlock in Skool — $10/mo →Bloodwork to run alongside RU58841
Baseline first, then again at 8–12 weeks.
| Marker | What it’s watching for |
|---|---|
| Total Testosterone | The baseline you can't reconstruct later |
| Free Testosterone | The fraction that does anything — total alone misleads |
| SHBG (Sex Hormone-Binding Globulin) | Explains a normal total sitting on top of a low free |
| Estradiol, Sensitive (LC/MS-MS) | The other half of the ratio, and the source of most symptoms |
| LH & FSH | Separates a testicular problem from a pituitary one |
The “Low T? Rule Out the Reversible Causes First” panel covers these in one order — 11 markers, $211.50 with the discount applied.
Check results you already have → · All 103 markers A–Z
RU58841 — frequently asked questions
What is RU58841?
RU58841 (PSK-3841) is a hormonal & sexual research compound. Non-steroidal androgen receptor antagonist designed for topical use — it blocks DHT AT the follicle rather than lowering it systemically, which is the entire appeal versus finasteride.
Is the full RU58841 protocol on this page?
The reported research dose is on this page, along with how RU58841 works and the evidence behind it. The protocol — how to work up to it, frequency, cycle length, time off, what not to stack it with and Coach Cam's notes — is inside Skool.
What is the half-life of RU58841?
RU58841 has an approximate half-life of Intended to be locally acting; systemic absorption in humans is not well characterized, which is part of what determines how often it's dosed.
What's the evidence behind RU58841?
Current evidence level: Animal and anecdotal only. No human trial has ever been published. RU58841 is offered for research purposes only and is not an approved medicine.
RU58841 inside a finished plan
One arm of 2 Protocol Blueprints, free to read in full.
What RU58841 is used for
RU58841 appears under 2 goals in the goal router.
Related Hormonal & Sexual compounds
Where this goes next
RU58841 is the dht & hair arm of this plan. The page above is the free breakdown of one compound; the plan it belongs to — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.