Encyclopedia · antiandrogen
RU58841
A topical androgen blocker from the 1990s that grew hair in animal and graft models but has no human efficacy trial and is sold online as a research chemical.
What it is
RU58841 is a non-steroidal antiandrogen developed for topical use on androgen-dependent skin conditions. Pan 1998 We found no approval for any use from the FDA, EMA or MHRA. Online vendors sell it as a "research chemical" and in unregulated hair products whose quality, purity and dose are unknown.
How it works
It competes with DHT at the androgen receptor. In cell work its potency was comparable to hydroxyflutamide. Pan 1998
What the studies show
- Human scalp grafts on mice (20 grafts, 6 months): more follicles recycled into a second hair cycle (28% vs 7%) and hair grew faster in treated grafts. De Brouwer 1997
- Macaques: it blocked DHT activation of the receptor in cells and increased hair density, thickness and length in bald stumptailed macaques, with no systemic effects detected. Pan 1998
- Prodrug (lab work): a myristate version converted to RU58841 in human skin cells, with negligible permeation through skin models. Munster 2005
- Humans (6 men, one dose): after a single topical 30 mg dose of a hair product, the parent drug and a metabolite appeared in dried blood spots, meaning considerable systemic exposure; steroid profile was unaffected. Okutan 2026
- No randomised human trial of RU58841 for hair loss was found.
Side effects and safety
There is no human safety trial. The 2026 data show absorption into the blood, which matters because the animal work was reported to show no systemic effects; systemic antiandrogen effects in people remain uncharacterised. Okutan 2026 Androgen receptor blockers as a class can affect a male fetus, so it is not for anyone who may be pregnant.
Bottom line
The evidence is animal, graft and lab data only: a plausible mechanism, but no human efficacy or safety data and no regulated supply. Better-supported topical antiandrogens are now in late trials; see clascoterone and pyrilutamide. Discuss with a doctor.
Fun facts
- Because it is a doping-control concern, the first human metabolism data came from an anti-doping laboratory in Cologne, not a hair clinic. Okutan 2026
Studies 4
De Brouwer B et al. Topical application of RU58841 on balding human scalp grafts in nude mice. Br J Dermatol. 1997
Tested: RU58841 1% in ethanol vs ethanol
Result: More follicles re-entered a second hair cycle (28% vs 7%) and hair grew faster in treated grafts.
Read the study ↗Pan HJ et al. RU58841 in PC3 cells and bald stumptailed macaques. Endocrine. 1998
Tested: topical RU58841
Result: Blocked DHT activation of the androgen receptor (potency similar to hydroxyflutamide in cells); raised hair density, thickness and length in macaques with no systemic effects detected.
Read the study ↗Munster U et al. RU 58841-myristate prodrug in lipid nanoparticles for topical treatment. Pharmazie. 2005
Tested: RU58841 myristate prodrug in lipid nanoparticles
Result: Prodrug converted to RU58841 in human skin cells with negligible permeation through skin models.
Read the study ↗Okutan A et al. Metabolism and elimination of RU 58841 in humans. Biomed Chromatogr. 2026
Tested: one topical 30 mg dose
Result: Parent drug and a metabolite were found in dried blood spots, showing considerable systemic exposure; steroid profile unaffected.
Read the study ↗Related
- ClascoteroneA topical androgen blocker already approved as an acne cream whose 5% scalp solution reported positive phase 3 results in men; it is not yet approved for hair.
- PyrilutamideA topical androgen blocker from the Chinese company Kintor that reported positive pivotal results in China; no peer-reviewed efficacy paper yet.
- FluridilA topical antiandrogen designed to break down in the skin; its only human evidence is one small 2002 trial by its inventors.
- FinasterideA prescription pill (and in some countries a scalp spray) that lowers DHT and is the best-proven drug for stopping male pattern hair loss.
- Antiandrogen comparison for hair lossA side-by-side of the drugs, topicals and supplements that work on the androgen pathway, with who they were studied in and how strong the evidence is.