STUDresearch · Non-peptide
RU-58841
Also known as
RU58841 · PSK-3841 · PSK3841 · RU 58841 · topical RU · 5% RU
Community talk. May be wrong. Not medical advice. Not a protocol. Not for human or animal use.
Non-peptide
Some talk
Local
Topical
Skin, hair & tissue remodeling
Local — a scalp liquid. Not a whole-body anti-androgen pill.
What people say
RU-58841 is an unapproved topical androgen-receptor antagonist. Targeted application does not mean zero systemic exposure: a 2026 six-volunteer study detected parent RU in blood after one topical dose.
Doses people talk about
Descriptive exposures, not a guide. Community products were unverified, and labeled concentration was demonstrably unreliable in the studied bottle.
How it may feel
Accounts conflict: one five-year user reported maintenance without noticed side effects; another said urinary symptoms resolved after stopping but mood effects remained below baseline four years later and libido recovery was not reported. A separate 0.5 mL 5% chest/pulse account resolved in three to four days after normal ER testing.
Short-term stacked report5% topical, 1 mL once daily
Used with topical finasteride/minoxidil/dutasteride, injectable GHK-Cu and TRT; the author said attribution was uncertain.
Single adverse report5% topical, 0.5 mL once
Chest tightness/palpitations, normal ER tests and resolution within three to four days were reported.
Controlled administration study30 mg topical once
Six healthy men; online bottle labeled 50 mg/mL assayed at 30 mg/mL.
Half-life & effect duration
- Half-life in the body
- Topical RU-58841No settled half-life estimate
- Felt duration people report
- One adverse accountPalpitations or chest tightness, recovering over 3–4 days
- Longer-use accountsSome symptoms resolved after stopping; others reportedly persisted
- Another accountTransient palpitations during the first 2–3 days, then no claimed cardiovascular issues
Cycles people discuss
Community use is daily maintenance over months or years, not a short cycle. Users report shedding after stopping, but accounts usually combine finasteride/minoxidil and do not establish withdrawal timing.
Timing
Community notes describe daily topical use, often in the evening so the product can sit; morning use also appears. This is reported practice, not a labeled regimen or a parent-drug half-life.
Stacks
Reports frequently include minoxidil, finasteride/dutasteride and sometimes microneedling. Combinations weaken attribution; pyrilutamide is usually discussed as a switch rather than a same-scalp partner.
Access talk
Not an approved drug, not 503A, not PSK-3841 trial material. Gray powder and premixed 5% bottles. Research-use-only labels.
Labs people mention
T / DHT often unchanged in old macaque talk and in the 2026 single-dose human steroid-profile arm. Unchanged hormones ≠ zero blood drug.
Watch for
Chest / heart-scare threads: Recurring r/tressless caution posts after two different symptomatic runs. Not a settled cardiology finding — still the scare that moves people to KX-826.
Tap a line to jump into the full notes. Research only — may be wrong.
Timing context & sources
Half-life in the body
The reviewed human study establishes systemic exposure and long detection windows, but not a terminal parent-drug half-life.
After one 30 mg topical scalp dose in six healthy men, parent RU was detected in dried blood spots from all six after dosing and peaked within 12 hours. Levels approached baseline by 36 hours; after 120 hours only one participant had low findings, including the final 168-hour sample. Urinary metabolites appeared as late as 213 hours.
Six-person single-dose analytical/doping study; detection windows cannot be converted into half-life, chronic exposure or clinical safety.
- Okutan et al. — Metabolism and elimination behavior of RU 58841 in humans (opens in a new tab)Six healthy men received one 30 mg topical scalp dose. Parent RU was detected in dried blood spots from all six after dosing and peaked within 12 h; levels neared baseline by 36 h, and after 120 h only one participant had low findings, including the final 168 h sample. Urinary metabolites persisted up to 213 h.Small single-dose analytical/doping study; detection windows are not half-lives; labeled 50 mg/mL product assayed at 30 mg/mL.
Felt duration people report
Community reports do not establish a consistent onset or duration of benefit or adverse sensations.
One user reported palpitations/chest tightness after 0.5 mL 5% and recovery in three to four days. A separate six-month user said urinary/prostate symptoms resolved after stopping, but mood effects remained below baseline four years later and libido recovery was not reported. Another 6–7-year stacked user claimed no cardiovascular issues while also describing transient heart-palpitations feelings during the first two or three days.
Anonymous, uncontrolled, unverified products, later D-phenylalanine use and major fin/min/other stack confounding prevent causal timing; normal ER tests do not establish cause or general safety.
- Reddit r/tressless — RU58841 is great, super fast acting (opens in a new tab)OP used 5% 1 mL daily alongside topical finasteride/minoxidil/dutasteride, injectable GHK-Cu and TRT, and admitted attribution was impossible. A distinct commenter reported chest tightness/palpitations after one 0.5 mL 5% use, normal ER tests, and recovery in 3–4 days.Anonymous unverified products, major stack confounding; acute report cannot establish causality/incidence.
- Reddit r/HairlossResearch — RU58841 long-term experience and side effects (opens in a new tab)One six-month user reported early/worsening depression, affected libido and urinary/prostate symptoms; urinary symptoms resolved after stopping, but mood remained below baseline four years later and later D-phenylalanine use confounded recovery. A distinct 6–7-year fin/min/RU user reported regrowth and shedding after over ten days off, claimed no CV issues, yet also described transient early palpitation feelings and low-test symptoms at higher concentration.Anonymous mixed products, later self-treatment and substantial stack confounding; identity, concentration and causality unverified.
- Reddit r/tressless — RU58841 long-term use and expectations (opens in a new tab)Five-year RU user reported regrowth/maintenance without noticed side effects, earlier inadequate response to finasteride alone, severe shedding during a May-to-update interruption, and improvement after restarting; concentration, volume and concurrent minoxidil were not stated.Anonymous and uncontrolled; stated finasteride history, but concentration, volume, other concurrent treatments and product identity were not established; no independent product/photo verification.
What people say
- Hold when fin is not enough: Common stack log — oral fin/dut + minox + RU on the hairline. Attribution is messy. forum
- Solo 90-day albums: A minority of YouTube/tressless solos claim shed-stop and some density without a 5-AR. Plenty of “nothing at 3 months” too. anecdote
- Why people pick it over more oral 5-AR: “Block the receptor on the scalp, leave serum DHT.” That is the pitch, not a proven zero-blood story. forum
- 2026 X/tressless read of the Cologne paper: Systemic exposure is now harder to deny; “T/E didn’t move after one dose” is not chronic safety. Heart-scare threads did not get a cardiology trial out of it. forumtrial
- Macaque 5%: Uno-style work is the graph vendors still screenshot. Stronger than 0.5%; not a human RCT. animal
- Graft-on-mouse 1%: De Brouwer 1997 — more second cycles and faster linear growth vs ethanol. animal
Doses people talk about
- Copied concentration: 50 mg/mL (5%) in ethanol/propylene glycol is the default mix. forum
- Inspected and broader daily amount: One short-term, heavily stacked report used 5% at 1 mL/day alongside topical finasteride/minoxidil/dutasteride, injectable GHK-Cu and TRT; attribution was uncertain. A separate five-year user reported regrowth/maintenance and a shedding interruption but did not state concentration or volume. Broader community talk remains about 0.5–1 mL once daily to thinning zones (~25–50 mg RU on the scalp). forum
- Lower experiment: 2–3% for sting or side-effect fear. Macaque data was weaker at 0.5%. forum
- Paper (grafts): 1% in ethanol, 5 days/week. animal
- Framing: DIY milligrams in a dropper — not a labeled drug. forum
- PSK-3841 program talk: 2.5% or 5% once daily vs vehicle in the unpublished 6-month design. trial
- Label vs lab: The 2026 internet bottle said 50 mg/mL; assay said 30. “I use 5%” is a vendor claim until tested. trial
How it may feel
- Days 1–14: Alcohol/PG sting, dryness, itch. No fin-brain-fog story for most. forum
- Weeks 2–8 shed: Some get a topical shed like minox. Others say the dump stopped. forum
- Months 3–6: Album window. If it is doing anything, this is when photos get posted — or when people call it a waste and switch to KX-826. forum
- Systemic-side cluster: A loud minority reports low mood, weak erections, chest tightness, or “heart attack scare” threads after weeks to months. Timing is inconsistent; identity of the powder is a confounder. forum
- Stop: No 5-AR washout. Vehicle irritation stops fast; any receptor block is gone with the bottle. forum
- Single-application adverse report: One commenter described chest tightness and palpitations after 0.5 mL of 5% RU, normal ER ECG/echo/blood results, and a same-author update saying they felt normal three to four days later. Product identity was unverified. forumanecdote
- Lower % is not a free pass: June 2026 HairlossResearch log — premixed 5% chest pain on a run; homemade 2.5% still breathless/cough; 0.5 mL next morning “couldn’t get out of bed.” Stopped; throat/chest quieted. forumanecdote
- Long-run minority: Aug 2026 thread still has “6–7 years, no sides under 5%” next to palpitations/facial-fat-loss/years-of-flat-mood quit stories. Identity of the powder is the confounder everyone names. forum
Around the dose
- Clock: Daily topical, often evening so it sits. Morning exists. forum
- Scalp: Apply to the thinning zone, wash hands. Not a systemic pin. forum
- After: Stay on it — hair anti-androgen talk is maintenance, not a weekend pulse. forum
- Chest / pulse the same week: Community stop rule — do not “push through” palpitations the way people push a minox shed. forum
- Hands off partners / broken skin. Topical NSAA common sense; the 2026 paper is why “it never leaves the follicle” is a weaker line now. forumtrial
- Don’t stack another topical AR blocker. RU → KX-826 is a switch, not a same-scalp double. forum
Cycles people discuss
- Daily topical while testing: 3–6 month photo tries, then keep or dump. forum
- Not a blast-and-cruise 5-AR. Miss a week and people argue about a shed. forum
- Stay-on like minox if they believe it — receptor block is not a one-and-done. forum
- Switch to pyrilutamide is the 2024–26 exit when RU sourcing or sides get loud. forum
- Heart/identity scare is the 2026 stay-off reason, not a planned cycle. People who keep it treat missed weeks as a shed risk. forum
Timing
- Once daily is the DIY ritual because that is how people mix a 30-day bottle, not because a label proved it. forum
- Evening application is common so it sits overnight and does not get washed to a pillow in the first hour. forum
- If sides show, people stop the same week — there is no 5-week dutasteride tail. forum
- Designed to be local and short: The 1990s pitch was rapid skin metabolism so less systemic anti-androgen. Human PK from a marketed product does not exist. trial
- DBS vs “it stays on the scalp.” 2026 Cologne work: parent in blood for a week after one topical dose. Rapid-metabolite talk still exists; zero-blood talk does not. trial
More on what it is
- Why people talk about it: r/tressless’s old “nuclear” topical — people who will not swallow more fin/dut, or who already do and still shed. 2026 volume is RU vs KX-826 (pyrilutamide) and “is this going to wreck my heart/liver.” forum
- Not Winlevi / not KX-826. Clascoterone is an approved acne cream (hair is Breezula-class 5%). Pyrilutamide is the China-trial topical AR blocker people switched to when RU sourcing got scary. forum
- What it is: A 1990s Roussel non-steroidal anti-androgen that never became a marketed hair drug. Later clinical-code talk is PSK-3841. Gray powder mixed into ethanol/PG is the real 2020s product. Not a peptide. trial
- How it works (plain): DHT still gets made. RU sits on the androgen receptor so DHT has a harder time telling the follicle to shrink. Different job than finasteride. trial
- Animal numbers people paste: 5% beat 0.5% on stump-tailed macaques; 1% ethanol on human balding grafts on nude mice helped a second hair cycle vs vehicle. No modern Phase 3. animal
- PSK-3841 trials (unfinished story): Early-2000s 2.5%/5% once-daily programs were registered; results were never a public label. That absence is why it is still a research chemical. trial
- 2026 identity paper people paste: Okutan et al. (Biomedical Chromatography, Aug 2026) bought an internet “5% / 50 mg/mL” serum — measured 30 mg/mL, no other drugs found. trial
- It did go systemic in that study. Dried blood spots detected parent RU in all 6 volunteers after one ~30 mg scalp dose; levels neared baseline by 36 h, and after 120 h only one volunteer had low findings, including the final 168 h sample. Urine showed metabolites, not parent, as late as 213 h. Single-dose steroid profile did not move. trial
Stacks
- + Minoxidil: Vehicle fights (PG on PG) and sting stack. Still the default add. forum
- + Fin/dut: DHT down plus receptor block — the “nuclear” log. forum
- + Microneedling: Same hair-stack culture; more sting on a needled scalp. forum
- Vs pyrilutamide, not with it, for most. Two topical AR blockers is usually a switch, not a stack. forum
- + Fin/dut + oral minox “nuclear” logs still exist in 2026 — including PED-hair bodybuilding diaries. Attribution is hopeless; heart-scare risk is what the caution posts are about. forum
Access talk
- Not an approved drug, not 503A, not PSK-3841 trial material. Gray powder and premixed 5% bottles. Research-use-only labels. forum
- Identity is the product: 2026 Cologne group bought a labeled 50 mg/mL internet serum and measured 30 mg/mL. Third-party tests on forums have also shown underdose or “not RU.” trialforum
- Not a July 2026 peptide PCAC story. Access is Discord/WhatsApp/research-chem — the same identity problem as a decade of tressless sourcing. forum
- Exit shelf people name: pyrilutamide / KX-826 when RU sourcing or sides get loud. Still not an approved hair AR blocker in the US. forum
Labs people mention
- No RU blood level in DIY logs. Heart-scare people get ECG/troponin in the ER, not a research-chem assay. forum
- T / DHT often unchanged in old macaque talk and in the 2026 single-dose human steroid-profile arm. Unchanged hormones ≠ zero blood drug. trialanimal
Storage notes
- Powder-in-vehicle is the whole product. Ethanol/PG (sometimes DMSO scare-stories). STUDresearch does not publish a mix chart. forum
- Light, cool, tight cap. RU solutions yellow and people argue about potency drop. forum
- Identity risk is the point: AliExpress / gray 5% is not PSK-3841 trial material. forum
Watch for
- Scalp sting / dryness / dermatitis: Ethanol/PG on a thinning hairline. The everyday limiter. forum
- Sexual / mood sides (minority, loud): Weak erections, flat mood, “it went systemic.” Contested; treated as a real stop-reason on the board. forum
- Chest / heart-scare threads: Recurring r/tressless caution posts after two different symptomatic runs. Not a settled cardiology finding — still the scare that moves people to KX-826. forum
- Powder identity: Concentration and purity are the product. forum
- Not a fin replacement with proof if DHT is the actual driver and you never blocked 5-AR. forum
- Keep off broken skin / away from partners — topical anti-androgen common sense in those threads. forum
- Heart-scare is the 2025–26 loud minority: palpitations, chest tightness, SOB, ER visits with clean ECGs, occasional rechallenge that lights it back up. Not a settled cardiology finding — still why people jump to KX-826. forumanecdote
- Identity scare is the other half: under-filled “5%,” wrong molecule, or synthesis junk. The 2026 assayed bottle was 30 mg/mL not 50. trialforum
- Facial-fat-loss / long mood-flattening quit stories sit next to the heart posts. Confounded, contested, treated as a stop-reason anyway. forum
- No modern human Phase 3. Graft-mouse and macaque ≠ a labeled hair drug. trial
Evidence mix
Mostly community / anecdote tags
Full: every bullet (trial + community). Use Scan for a faster bro-science read.