RU58841

weak data

Also seen as: RU58841 + Minox Blend, PSK-3841, HMR-3841, RU58841 Minoxidil, RU/Minox Blend

The Dose Guy’s verdict

Sep 1, 2026
4 sources

The original topical antiandrogen, with a real following, a plausible mechanism, and zero human trials. RU58841 works in primates, works in scalp grafts, and the community has run it for over a decade. None of that is a substitute for knowing what it does inside a person long-term. If you want a topical antiandrogen, pyrilutamide is the more interesting bet now, because at least someone is doing the human work. Either way, finasteride and minoxidil are still the foundation.

Would I take it?Caution, you're the trial.

What it is

A nonsteroidal androgen receptor antagonist developed by Roussel-Uclaf in the 1990s and abandoned before it ever reached human trials. You mix raw powder into a solution and apply it to your scalp, where it competes with DHT for the androgen receptor on your hair follicles. The pitch: block the hormone that shrinks your hair, locally, without touching your systemic hormone levels the way finasteride does. The preclinical work was promising. In a macaque model of androgenetic alopecia, topical RU58841 grew hair with no detectable systemic effects. The reason it never went further is probably commercial, not scientific, but the outcome is the same: nobody ran the human trials, and you are the trial.

That makes it a research chemical in the full sense. You buy powder from a vendor, you mix it yourself, and the quality control is a COA you hope is honest. Pyrilutamide is the newer compound chasing the same mechanism through real clinical development, which is why I rank it as the more interesting bet despite RU58841 having far more community mileage.

What the research shows

No human trials. Zero. Everything below is animal or in-vitro work. Read it as “interesting,” not “evidence it works in you.”

The preclinical work is extensive for a compound that never reached humans, with one result worth knowing: in a cotransfection assay, RU58841 promoted androgen receptor activity instead of blocking it. In simpler cell assays without the coactivator, it blocked cleanly. Nobody has tested what that means in living skin. All of the data is from the late 1990s:

Topical RU58841 increased hair density, thickness, and length in a macaque model of androgenetic alopecia, with no detectable systemic effects.Endocrine 1998 · macaque

RU58841 promoted androgen receptor interaction with coactivator ARA70 and enhanced receptor transcriptional activity when both were cotransfected into DU145 cells.PNAS 1998 · in vitro · cotransfection

In human balding scalp grafts on testosterone-conditioned nude mice, topical RU58841 produced significantly higher linear hair growth rates than ethanol control, p < 0.04.Br J Dermatol 1997 · scalp grafts · n=20 grafts

Topical 1% RU58841 for two months produced sebaceous regression equivalent to castration in rats, with no significant changes in serum testosterone or DHT.Dermatology 1997 · rat

No clinical trial testing RU58841 in living human participants exists in the published literature.as of Aug 2026

Realistic protocols

The community has been running RU58841 for over a decade, so the protocol is well-established even though the evidence behind it is not. You buy raw powder, dissolve it in a vehicle, the standard being 70/30 ethanol and propylene glycol or a pre-mixed KB solution, and apply it to your scalp once daily. The consensus concentration is 5%, which comes from early forum experiments, not preclinical or human data. The studies used 1%. Most people apply at night, let it dry, and go to bed.

The compound degrades in water, so the vehicle and storage matter. Keep it in an anhydrous solution, mix in small batches, and refrigerate what you are not using. Pre-mixed solutions from vendors save the hassle but add a trust layer you cannot verify without independent testing.

The practical tell is shedding. A few weeks in, some people see increased hair fall as the antiandrogen resets affected follicles into a new growth cycle. That is the expected mechanism, not a sign it is failing. Judge by photos at month three, not the shower drain at week two. And understand this is maintenance: hair you gain while using it will regress when you stop.

Concentration5% (50 mg/mL)Community standard. Preclinical heritage, not human dose-finding.

FrequencyOnce dailyApplied to scalp and left to dry. Most run it at night.

VehicleEthanol/PG or KBDegrades in water. Anhydrous vehicle, small batches, refrigerate.

DurationOngoingEffects reverse when you stop. This is maintenance, not a course.

Side effects

No human safety data exists. Everything here is community-reported:

anecdotalScalp irritation, dryness, and flaking, usually from the vehicle more than the compound. Switching vehicles often fixes it.

anecdotalInitial shedding in the first weeks, consistent with follicle-cycle reset.

anecdotalHeart palpitations and chest tightness, reported by a small minority. Hard to attribute without pharmacokinetic data, but stop and reassess if they show.

anecdotalMood changes, lowered libido, and rare gynecomastia reports from long-term users. These are the systemic antiandrogen signals you would expect if the compound reaches your bloodstream.

unknownNo human safety data exists at any timepoint. You are running a compound abandoned before phase 1, for years, without published data on its systemic absorption, metabolism, or long-term profile.