RU-58841

An abandoned 1990s French pharmaceutical candidate — a topical antiandrogen designed to block DHT at the hair follicle without (in theory) finasteride's systemic suppression. Development died in corporate transitions; it survives only as an unapproved product.

RU58841 is a non-steroidal androgen receptor antagonist designed to be applied to the scalp and act locally — blocking the receptor in hair follicles so DHT cannot signal there, without lowering DHT systemically the way finasteride does. That local-only premise is the entire appeal and it is also the unresolved question: whether it stays local at the amounts people apply has never been established in a human study.

Animal studies (notably the macaque hair-growth work) plus early human safety trials from the original program. It never completed efficacy trials in people — the large online testimonial base is uncontrolled self-experimentation on a compound with no finished dossier.

• Two human randomised vehicle-controlled trials were REGISTERED AS COMPLETED — a four-week safety and pharmacokinetic study and a six-month efficacy and safety study. Neither has publicly accessible results, so efficacy, effect size, enrolment and safety cannot be verified. That is different from no trials existing, and it is also not evidence that it works.
• Development did not proceed to approval. The reasons are not publicly documented in a way that supports any confident account, and the frequently repeated stories about why — reassuring and alarming alike — are speculation.
• The animal and ex-vivo work that exists showed local antiandrogen activity, which is why the idea persists.
• The local-only premise no longer holds. A 2026 controlled study applied it topically to six healthy men and detected the parent compound and metabolites in blood and urine, concluding that topical use produced considerable systemic exposure. Users also report systemic symptoms — low mood, reduced libido, fatigue — which are uncontrolled reports that cannot establish frequency or causation. What the analytical work shows is that systemic exposure happens whether or not anyone notices symptoms.
• It is sold as an unapproved research chemical with no verified identity, concentration, purity, stability or quality control.

Applied topically. Systemic exposure after a single topical application HAS now been demonstrated in humans, which removes the central assumption its use rests on. What remains unknown is how much exposure varies across products and formulations, and what chronic exposure does. Anything increasing skin penetration would be expected to raise it further.

Long-term human safety, systemic exposure, and product stability are not established. Its metabolite is a potent antiandrogen, and the systemic effects of chronic scalp application were never characterized; anecdotal reports of libido or mood changes exist but are not established effects. No approved formulation means no concentration or purity standard.

• Anyone unwilling to accept an unapproved research chemical whose efficacy has never been publicly demonstrated and whose chronic safety is uncharacterised
• Anyone pregnant, breastfeeding or trying to conceive — antiandrogens carry fetal risk and this one is unstudied
• Unresolved rather than established risks worth weighing: mood symptoms are reported but not causally attributed, and compromised or penetration-enhanced skin would be expected to increase absorption

• No characterised human interaction profile exists.
• Microneedling, tretinoin and anything else that increases skin penetration would be expected to raise systemic exposure.
• Other antiandrogens, where systemic effects would compound if absorption is occurring.

• There is no established monitoring for an uncharacterised research chemical, and offering a panel would imply a safety profile nobody has measured.
• There is no validated symptom-based way to tell whether the compound is reaching your bloodstream — the analytical work shows systemic exposure occurs regardless of symptoms, so absence of symptoms proves nothing. Any new or serious symptom warrants medical assessment on its own terms.
• Scalp irritation, which is common with these preparations.

Whether it produces or maintains clinically meaningful hair growth has never been established in publicly reported results, so what happens after stopping is equally unestablished. No withdrawal syndrome is described. Anyone who developed symptoms while using it should mention it to a clinician rather than assume they resolve — chronic exposure and recovery have not been characterised.

US: not FDA-approved for any use.

Papers about this compound, not proof of the claims above. A title says what was studied, which is sometimes a negative result or a different question entirely.

• RU 58841-myristate--prodrug development for topical treatment of acne and androgenetic alopecia
  Pharmazie, 2005
• 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

• RU 58841, a new specific topical antiandrogen: a candidate of choice for the treatment of acne, androgenetic alopecia and hirsutismJ Steroid Biochem Mol Biol · 1994
• Local inhibition of sebaceous gland growth by topically applied RU 58841Ann N Y Acad Sci · 1995
• RU 58841-myristate--prodrug development for topical treatment of acne and androgenetic alopeciaPharmazie · 2005
• Preliminary pharmacokinetics and metabolism of novel non-steroidal antiandrogens in the rat: relation of their systemic activity to the formation of a common metaboliteJ Steroid Biochem Mol Biol · 1994
• Synthesis and structure-activity studies of side-chain derivatized arylhydantoins for investigation as androgen receptor radioligandsBioorg Med Chem Lett · 2001
• Importance of sebaceous glands in cutaneous penetration of an antiandrogen: target effect of liposomesJ Pharm Sci · 1997
• Inhibition of hair growth by testosterone in the presence of dermal papilla cells from the frontal bald scalp of the postpubertal stumptailed macaqueEndocrinology · 1997
• Cyproterone acetate loading to lipid nanoparticles for topical acne treatment: particle characterisation and skin uptakePharm Res · 2007
• Promotion of agonist activity of antiandrogens by the androgen receptor coactivator, ARA70, in human prostate cancer DU145 cellsProc Natl Acad Sci U S A · 1998
• Evaluation of RU58841 as an anti-androgen in prostate PC3 cells and a topical anti-alopecia agent in the bald scalp of stumptailed macaquesEndocrine · 1998
• 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 miceBr J Dermatol · 1997