RESEARCH MONOGRAPH · KDC-MN-281

RU58841

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 3 min read

Our opinion on this compound

58/100

The forum-favorite topical AR antagonist that never made it past phase 2, but the mechanism is genuinely interesting

Look, RU58841 is one of those compounds where the research story and the internet story have completely diverged. Roussel-Uclaf developed it in the 90s as a topical androgen receptor antagonist with the explicit goal of getting AR blockade locally without crashing systemic testosterone. Mechanistically it's a non-steroidal antiandrogen that binds AR with reasonably high affinity and (importantly) gets rapidly cleared by hepatic esterases if it reaches circulation. That last bit is the whole pitch.

The hair loss forums treat this thing like it's an approved drug. It's not. Development stopped at phase 2 in the late 90s when Roussel-Uclaf got swallowed by what became Sanofi, and the compound just sat there. ProStrakan picked it up briefly under PSK-3841 and then dropped it too. So we're working off a small primate study (the famous stumptailed macaque work), a couple of human phase 1/2 reports, and a lot of self-reported research from people running it on themselves.

What we like: the local-clearance design is elegant in theory, and the in vitro AR antagonism is real. The macaque data showed actual hair regrowth at concentrations that didn't move systemic androgens much.

What we dont like: zero long-term human safety data. The reason development stopped isn't fully public, but the bet that hepatic clearance fully protects from systemic exposure has never been proven at the duration scales people actually use this. Skin absorption with carrier solvents (ethanol, propylene glycol, the usual) is hard to model. And the literature is genuinely thin, which the marketing volume doesnt reflect.

Sourcing is a bigger problem than people admit. RU58841 isn't manufactured at pharma scale anywhere, so what you're buying is small-batch research-grade from Chinese suppliers with variable QC. HPLC purity reports help, but theyre not the same as actual pharmacopoeia oversight.

For lab work on AR biology in skin and follicle models, it's a useful tool compound. As a research molecule with thousands of hours of self-experimentation behind it but a fraction of a percent of the human data we'd want? thats the gap. We keep it stocked because the mechanism work is real and the demand isnt going away, but the evidence base is genuinely partial.

Evidence: 35
Mechanism: 70
Reliability: 55
Safety: 50
Sourcing: 65
Value: 60
Signal: 72
Staying power: 55

Plain-language summary Intrigue 55 / 100

RU58841 is a topical androgen receptor blocker developed by Roussel-Uclaf in the 1990s as a hair-loss treatment. The idea was elegant: rather than systemically lowering DHT (and risking sexual side effects), apply an AR blocker directly to the scalp where it competes with DHT at the hair follicle, with minimal absorption into the rest of the body. Phase 1 and 2 trials showed efficacy in slowing or reversing male-pattern baldness, but the compound was abandoned commercially (the reasons remain unclear and the compound was simply shelved). It is now used in DIY scalp solutions sourced as a research chemical, with minimal long-term safety data and no manufacturer accountability. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Topical androgen receptor antagonist

A topical non-steroidal AR antagonist developed for androgenetic alopecia; never advanced to commercial development but widely used as a research compound.

Abstract

RU58841 (PSK3841; CAS 154992-24-2; molecular formula C17H18F3N3O3; molecular weight 369.34) is a non-steroidal androgen receptor antagonist developed at Roussel-Uclaf (now Sanofi) in the 1990s as a topical treatment for androgenetic alopecia. The compound is structurally a hydantoin and binds the AR with sufficient affinity to compete with DHT in scalp tissue. Topical application allows local AR antagonism in hair follicles with minimal systemic absorption, theoretically avoiding the sexual side effects of systemic 5AR inhibitors. Phase 1 and 2 trials demonstrated efficacy in slowing or reversing scalp hair loss. Development was discontinued at Roussel-Uclaf (subsequent corporate merger and prioritization). The compound entered the research-grade and DIY hair loss community via the published patents and has remained in informal use without regulatory approval. Used as a reference topical AR antagonist in dermatologic and androgen pharmacology research.

Mechanism of action

Topical non-steroidal AR antagonist; competitive blockade of AR in scalp tissue. Minimal systemic absorption with topical application.

Reported research dose ranges

DIY topical use commonly 5 percent solution, 1 mL applied to scalp daily. No clinical trials in current development.

References

Battmann T, et al. Pharmacological profile of RU58841, a novel non-steroidal antiandrogen. Eur J Pharmacol 1998.
Munster U, et al. RU58841-myristate: prodrug development for topical treatment of acne and androgenetic alopecia. Pharmazie 2005.
Sintov AC, et al. Topical antiandrogens: properties and use. Drugs 2001.

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The full reference document is available as a research-use-only PDF download. Note: PDFs for newly added compounds may take a few hours to propagate after this article was published.

KDC-MN-281

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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RU58841

Abstract

Mechanism of action

Reported research dose ranges

References

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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