RU 58841 is a nonsteroidal antiandrogen: a molecule that blocks the androgen receptor, the protein that testosterone and dihydrotestosterone (DHT) act through. Researchers at the French company Roussel Uclaf developed it as a topical treatment for androgen-driven skin conditions such as acne, male-pattern hair loss (androgenetic alopecia) and hirsutism (Battmann et al., J Steroid Biochem Mol Biol 1994). Today it is sold online, mostly as a scalp solution for hair loss.
The most important fact is how little is known in people. RU 58841 has never received regulatory approval, and no controlled human trial of its effect on hair, skin or safety has been published. The only published human study, from 2026, gave a single scalp dose to six men and found that the drug reaches the bloodstream in measurable amounts (Okutan et al., Biomed Chromatogr 2026).
This page summarizes what the animal studies and that single human study report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Nonsteroidal androgen receptor antagonist (N-substituted aryl hydantoin) |
| Origin | Roussel Uclaf research center, France; first published 1994; also coded PSK-3841 and HMR-3841 |
| Approval | None; never approved by any regulator |
| Route studied | Topical solution (animals, human scalp grafts); one single-dose human scalp study |
| Studied doses | 1% solutions in animal and graft studies; a single 30 mg scalp dose in the only human study |
| Half-life | About 1 h after IV dosing in rats; no human half-life published |
| Human exposure | Detected in blood of all 6 men after one scalp dose, up to 168 h |
| US status | Not an approved drug; not listed as a Schedule III anabolic steroid |
| WADA status | Not named on the 2026 Prohibited List |
What it is
RU 58841’s chemical name is 4-[3-(4-hydroxybutyl)-4,4-dimethyl-2,5-dioxoimidazolidin-1-yl]-2-(trifluoromethyl)benzonitrile. Its formula is C₁₇H₁₈F₃N₃O₃ and its molecular weight is 369.34 g/mol (PubChem). It is not a steroid. It belongs to a series of aryl hydantoins and thiohydantoins that Roussel Uclaf built as androgen receptor blockers (Cousty-Berlin et al., J Steroid Biochem Mol Biol 1994).
It works at a different step than the 5α-reductase inhibitors finasteride and dutasteride, which lower the conversion of testosterone to DHT. RU 58841 instead competes with androgens for the receptor itself, like the oral antiandrogen bicalutamide (Okutan et al., 2026). In rats treated on the skin for 2 months, it did not change blood testosterone or DHT (Ye et al., Skin Pharmacol 1997). Minoxidil, the other common hair-loss treatment, is covered on its own page.
The design goal was a drug that blocks androgens in skin while leaving the rest of the body alone. In rats, RU 58841 itself left the blood quickly, and it formed very little of a slowly cleared, systemically active breakdown product. The developers argued this explained why it acted locally without systemic effects in animals (Cousty-Berlin et al., 1994). The 2026 human study, described below, challenges the idea that it stays local.
How it behaves in the body
Animal data
In rats given 10 mg/kg intravenously, RU 58841 had an elimination half-life of about 1 hour. Only about 1% of the dose was converted to the N-desalkyl metabolite (a breakdown product that has lost its side chain), RU 56279. That metabolite is antiandrogenic and is cleared much more slowly (Cousty-Berlin et al., 1994).
On skin, the sebaceous glands appear to be the main route of entry. In hairless rats, 3–4 times more RU 58841 was absorbed over 24 hours through normal skin than through scar skin that lacks sebaceous glands (Bernard et al., J Pharm Sci 1997). A fatty-acid prodrug, RU 58841-myristate, showed only negligible permeation through reconstructed human epidermis and pig skin within 6 hours in the lab (Münster et al., Pharmazie 2005).
The only human study
In 2026, researchers at the German Sport University Cologne gave six healthy men a single 1 mL application of an RU 58841 hair serum bought online, applied to the scalp. The product was labeled 50 mg/mL but measured 30 mg/mL, so each man received 30 mg (Okutan et al., 2026; PMC full text).
| Finding | Result |
|---|---|
| Parent drug in blood (dried blood spots) | Detected in all 6 men |
| Time to highest levels | Within the first 12 h |
| Highest concentration observed | About 5 µg/mL |
| Return toward baseline | Near baseline by 36 h; traces in one man after 120 h; detectable up to 168 h |
| Parent drug in urine | Not detected |
| Urinary metabolites | Five, formed by oxidation, side-chain removal (N-dealkylation) and glucuronidation |
| Longest urine detection | Glucuronide metabolites up to 213 h |
| Urinary steroid profile | No change after the single dose |
The authors concluded that RU 58841 is systemically available after scalp application and therefore has the potential to cause systemic effects. One urinary metabolite is an acyl glucuronide, a chemically reactive type of conjugate. With six men and one dose, the study cannot describe effects of daily long-term use, which the authors flagged as unstudied.
Regulatory status
- Approval. RU 58841 has no regulatory approval for any use; it is nonetheless sold by online suppliers (Okutan et al., 2026).
- Clinical trials. No published randomized trial in people exists for hair loss, acne or hirsutism.
- US controlled substances. It is not a steroid and is not among the anabolic steroids listed in Schedule III (21 CFR 1308.13).
- Sport. It is not named on the WADA 2026 Prohibited List. The hormone modulator class (S4) lists aromatase inhibitors, anti-estrogenic substances, agents preventing activin receptor IIB activation and metabolic modulators, but not androgen receptor antagonists. A single 30 mg dose did not change the urinary steroid profile used in doping control.
What the research shows
All efficacy data come from cell culture, animals or human scalp tissue grafted onto mice.
Androgen receptor blocking in cells
In human prostate cancer cells (PC3) engineered to express the androgen receptor, RU 58841 blocked DHT activation of the receptor. Its potency was comparable to hydroxyflutamide, and it did not activate the receptor on its own (Pan et al., Endocrine 1998). In a different prostate cell line (DU145), however, RU 58841 and other antiandrogens, including bicalutamide, increased receptor activity when the coactivator protein ARA70 was added. This shows that “pure antagonist” behavior can depend on the cellular setting (Miyamoto et al., PNAS 1998).
Hair growth in animal models
- Stump-tailed macaques. This monkey develops androgen-driven frontal baldness after puberty. Topical RU 58841 produced a “potent increase in density, thickening, and length of hair” on the bald scalp, with no systemic effects detected (Pan et al., 1998; Obana et al., Endocrinology 1997). The abstracts do not report the number of animals or effect sizes.
- Human scalp grafts on mice. Twenty scalp grafts from balding men were placed on female nude mice that were given testosterone. Ten grafts received 1% RU 58841 in ethanol and ten received ethanol alone, 5 days a week, with monthly hair counts for 6 months (De Brouwer et al., Br J Dermatol 1997).
| Outcome (graft study) | RU 58841 1% | Ethanol control |
|---|---|---|
| Active follicles | 29 | 28 |
| Follicles entering a second hair cycle | 8 (28%) | 2 (7%) |
| Linear hair growth rate | Significantly higher (p under 0.04) | Reference |
The authors said these results encouraged a clinical trial. No such trial has been published since.
Sebaceous glands (acne model)
Oil glands in skin enlarge in response to androgens, which is relevant to acne.
| Model | Dose and duration | Result |
|---|---|---|
| Hamster flank organ (Battmann et al., 1994) | Topical, from 1 µg per animal | Dose-dependent shrinkage; no effect on internal sex organs or testosterone up to 100 µg per animal |
| Hamster ear (Matias and Gaillard, Ann N Y Acad Sci 1995) | 10 µg/day topically for 4–12 weeks | Up to 60% smaller glands; untreated ear unaffected; glands back to normal within 4 weeks of stopping |
| Fuzzy rat (Ye et al., Skin Pharmacol 1997) | 1% solution for 2 months | Gland and duct shrinkage equal to castration; no change in blood testosterone or DHT; prostate weight not reduced |
In the hamster study, 300 µg injected under the skin gave only the same flank-organ effect as 1 µg applied topically, supporting a local rather than systemic action in that species.
Side effects and risks
No human safety data
No study has reported side effects of RU 58841 in people. The 2026 human study measured drug levels and urinary steroids after one dose. It did not assess adverse effects, and it did not study repeated use. The absence of reported harms reflects the absence of studies, not evidence of safety.
Systemic exposure
Animal work suggested RU 58841 acts locally, and older descriptions of it as “topical only” rest on those data. In humans, one scalp application produced blood levels detectable for days in every participant (Okutan et al., 2026). The authors noted that this gives it the potential for systemic effects. They also point out that blocking the androgen receptor body-wide reduces the receptor’s feedback signal, which can raise luteinizing hormone (LH) and androgen levels. For the effects seen with an approved oral drug of this class, see the bicalutamide page. Whether daily scalp use of RU 58841 causes such effects has not been studied.
Product quality
RU 58841 is available only from unregulated suppliers. The one product tested in the human study contained 30 mg/mL against a labeled 50 mg/mL, 40% less than stated, although no other drugs were detected (Okutan et al., 2026). Dose, purity and sterility of such products are not verified by any regulator.
Key takeaways
- A topical androgen receptor blocker that was never approved. Roussel Uclaf developed it for hair loss, acne and hirsutism (first published in 1994), but it was never approved.
- No human efficacy trials. Evidence for hair growth comes from macaques and from human scalp grafts on mice, where 28% vs 7% of follicles started a new growth cycle.
- It does reach the blood. In the only human study, one 30 mg scalp dose was detected in the blood of all six men for days, contradicting the “stays local” picture from animal studies.
- Safety is unknown. No study has reported adverse effects or long-term outcomes in people.
- Unregulated products. The one product tested contained 40% less drug than its label stated.
- Not scheduled or listed. It is not a US Schedule III steroid and is not named on the WADA 2026 list.
Sources
- Battmann T, Bonfils A, Branche C, et al. 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;48(1):55–60. PubMed.
- Cousty-Berlin D, Bergaud B, Bruyant MC, et al. Preliminary pharmacokinetics and metabolism of novel non-steroidal antiandrogens in the rat: relation of their systemic activity to the formation of a common metabolite. J Steroid Biochem Mol Biol. 1994;51(1-2):47–55. PubMed.
- Okutan A, Krug O, Fußhöller G, et al. Investigation into the metabolism and elimination behavior of RU 58841, and its influence on the steroid profile in humans. Biomed Chromatogr. 2026;40(10):e70602. PubMed; PMC.
- National Center for Biotechnology Information. RU 58841, compound summary (CID 132981). PubChem.
- Bernard E, Dubois JL, Wepierre J. Importance of sebaceous glands in cutaneous penetration of an antiandrogen: target effect of liposomes. J Pharm Sci. 1997;86(5):573–578. PubMed.
- Münster U, Nakamura C, Haberland A, et al. RU 58841-myristate–prodrug development for topical treatment of acne and androgenetic alopecia. Pharmazie. 2005;60(1):8–12. PubMed.
- Pan HJ, Wilding G, Uno H, et al. 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;9(1):39–43. PubMed.
- Miyamoto H, Yeh S, Wilding G, Chang C. Promotion of agonist activity of antiandrogens by the androgen receptor coactivator, ARA70, in human prostate cancer DU145 cells. Proc Natl Acad Sci U S A. 1998;95(13):7379–7384. PubMed.
- Obana N, Chang C, Uno H. Inhibition of hair growth by testosterone in the presence of dermal papilla cells from the frontal bald scalp of the postpubertal stumptailed macaque. Endocrinology. 1997;138(1):356–361. PubMed.
- De Brouwer B, Tételin C, Leroy T, et al. 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;137(5):699–702. PubMed.
- Matias JR, Gaillard M. Local inhibition of sebaceous gland growth by topically applied RU 58841. Ann N Y Acad Sci. 1995;761:56–65. PubMed.
- Ye F, Imamura K, Imanishi N, et al. Effects of topical antiandrogen and 5-alpha-reductase inhibitors on sebaceous glands in male fuzzy rats. Skin Pharmacol. 1997;10(5-6):288–297. PubMed.
- Code of Federal Regulations. 21 CFR 1308.13, Schedule III. eCFR.
- World Anti-Doping Agency. 2026 Prohibited List. WADA.