RU58841

What RU58841 is

RU58841 is a small synthetic molecule, neither a hormone nor a steroid. The Roussel Uclaf research group described it in 1994 as a topical antiandrogen, that is, an agent that, applied to the skin, curbs the effect of male hormones. As targets they named acne, hereditary hair loss and excessive body hair in women. It never reached approval. Today it is offered online as a research chemical and as a hair serum.

The idea behind it is tempting for many men with hair loss: androgen blockade where it is needed, without the body-wide hormone reduction that comes with finasteride and dutasteride. What is rated here is the state of knowledge, and so far it ends before the first efficacy study in humans.

How it works

Hereditary hair loss occurs when dihydrotestosterone (DHT), acting via the androgen receptor, gradually shrinks the hair follicles. Finasteride and dutasteride lower DHT production. RU58841 acts one step later and occupies the receptor itself. In prostate cancer cells it inhibited the effect of DHT about as strongly as hydroxyflutamide, the active form of the prostate cancer drug flutamide.

The idea was that the substance stays in the skin. In hamsters, an androgen-dependent skin organ regressed even with very small amounts on the skin, without any effect on the internal sex glands and without a change in testosterone levels; injected under the skin, a multiple of the amount was needed for the same effect. In humans, precisely this assumption has not been confirmed: after a single application to the scalp, doping analysts in Cologne found the active substance in the blood.

What the studies show

Battmann 1994: the starting point

The Roussel Uclaf research group showed in hamsters that RU58841 on the skin shrank an androgen-dependent skin organ in a dose-dependent manner, without any effect on the internal sex glands and without altering testosterone levels. In rats, small amounts had no effect by any route. From this the authors concluded that RU58841 could treat acne, hair loss and excessive body hair locally.

De Brouwer 1997: human scalp on mice

Twenty pieces of scalp from bald areas of men were grafted onto female nude mice that received testosterone through the skin. Ten grafts each were treated in a blinded manner with RU58841 solution or with the solvent alone and followed for six months. Under RU58841, 8 of 29 active follicles (28 percent) entered a second hair cycle, under solvent 2 of 28 (7 percent); the hair grew significantly faster (p less than 0.04). The authors saw this as a reason for a clinical trial. To this day, no such trial has been published.

Pan 1998: cells and monkeys

In prostate cancer cells, RU58841 inhibited the effect of DHT at the androgen receptor as strongly as hydroxyflutamide. On the bald forehead of stump-tailed macaques, density, thickness and length of the hair increased markedly, without detectable effects in the rest of the body. The authors themselves pointed out that such an effective receptor blocker could act throughout the body if it is absorbed through the skin.

Okutan 2026: the first study in humans

The Center for Preventive Doping Research at the German Sport University Cologne studied for the first time what the human body does with RU58841. Six healthy men applied once to the scalp a hair serum containing RU58841 bought online, whose purity had been checked beforehand. Five metabolites were found in the urine, one of them in one participant even after 213 hours. In capillary blood, the active substance itself and one metabolite were detectable, which the authors interpret as considerable absorption into the body. The steroid profile in the urine, which is measured in sport for the Athlete Biological Passport, remained unchanged. The study says nothing about the effect on hair.

Where the data stop

• Effect in humans. No study has tested whether RU58841 on the scalp slows hair loss or brings hair back in humans. ClinicalTrials.gov lists no entry (queried October 7, 2026).
• The local effect. The central promise that the active substance stays in the skin comes from experiments in hamsters and monkeys. In humans it was measurable in the blood after a single application; what happens with daily use over months has not been studied.
• Hormonal consequences. Whether the absorbed amounts affect libido, potency, breast tissue or the hormone balance has never been recorded. All that is known is that the steroid profile in the urine stayed the same after a single application.
• Products from the internet. No authority checks what is sold as RU58841; content, purity and solvents depend on the seller. More on this under gray market.

Status, approval and legal

RU58841 is not approved as a medicine anywhere, and no clinical trial is registered at ClinicalTrials.gov. In Germany it is listed neither in the German Narcotics Act nor in the German Ordinance on Prescription-Only Medicines. It is offered as a research chemical or as a hair serum without any authority having checked its quality or safety.

In sport, according to the wording of the WADA Prohibited List, it falls under S0, the non-approved substances, and is therefore banned at all times. The 2026 Cologne study describes the metabolites that doping laboratories can look for and shows that a single application does not distort the steroid profile in doping controls.

Safety

For RU58841 there are no tolerability data from studies in humans. The only human study was designed for metabolism and detection, not for side effects. All that is established is this: the active substance enters the blood after application to the scalp, and metabolites remain in the body for days.

What follows from this is open. Data on women, pregnancy, fertility and use over months do not exist. Anyone who wants to know how proven hair loss treatments perform will find the study situation under minoxidil, finasteride and dutasteride.

Sources

• Battmann T et al., J Steroid Biochem Mol Biol 1994 – RU 58841 as a new topical antiandrogen, experiments in hamsters and rats
• Matias JR, Gaillard M, Ann N Y Acad Sci 1995 – local inhibition of the sebaceous glands on the hamster ear
• De Brouwer B et al., Br J Dermatol 1997 – RU58841 on human scalp grafts on nude mice, controlled study
• Pan HJ et al., Endocrine 1998 – RU58841 in prostate cancer cells and on the bald scalp of stump-tailed macaques
• Münster U et al., Pharmazie 2005 – RU-58841 myristate as a prodrug in lipid nanoparticles
• Okutan A et al., Biomed Chromatogr 2026 – metabolism and excretion of RU 58841 in humans, 6 men, single application to the scalp
• WADA Prohibited List 2026, informational German translation by NADA – S0 non-approved substances