If you're already on oral or topical finasteride and minoxidil and you still want a third lever — or you're running AAS and need an androgen receptor blocker that doesn't tank your systemic DHT — the decision usually collapses to RU58841 or pyrilutamide (KX-826). Both are topical AR antagonists, both have decades (RU) or years (pyri) of self-experimentation behind them, and both are good enough that the choice comes down to kinetics, sides profile, and cost. Here's how the community actually sorts it out.
The mechanistic difference that matters#
Both compounds compete with DHT at the androgen receptor locally in the scalp. Neither lowers serum DHT the way a 5-AR inhibitor does, which is exactly why they're attractive for people who can't tolerate fin/dut or who are running exogenous androgens and don't want to blunt systemic anabolism.
The practical separation:
- RU58841 is a potent, non-steroidal AR antagonist with a longer local residence time. It sticks around on scalp ARs, which is why once-daily dosing works, but it also means more compound is available to drift systemically if you over-apply or use a high-penetration vehicle.
- Pyrilutamide (KX-826) was engineered specifically to degrade rapidly after skin penetration. The design goal was local activity without systemic androgen blockade — less gyno risk, less libido impact, cleaner bloodwork. Community consensus on tressless consistently reflects this: pyri users report fewer systemic complaints at equivalent application frequency.
In other words: RU is the older, harder-hitting tool. Pyri is the cleaner, more forgiving tool. Neither of those is automatically better — it depends on what you're trying to solve.
What long-term users are actually reporting#
Filtering through years of logs on tressless and MESO, a few patterns are clear:
- RU58841 produces more visible regrowth in hard responders. People with aggressive MPB who plateau on fin+min frequently report density gains after adding RU at 50-70 mg/day. This is the compound with the most before/after photo evidence going back 15+ years.
- Pyrilutamide is closer to maintenance-tier for many. Phase 3 data out of China showed modest efficacy — real, but not dramatic. Self-experimenters echo this: good for holding ground, less impressive for regrowing a slick NW3.
- Sides profile tilts clearly toward pyri. Users who got gyno twinges, brain fog, or libido dips on RU often switch to pyri and clear up. The user discussion on tressless includes several accounts of exactly this swap.
- Itch relief is underrated. Multiple RU users describe eliminating chronic scalp itch and then seeing regrowth — a reminder that inflammation is part of the AGA picture and a strong AR blocker addresses it directly.
"Pyrilutamide has less systemic effects because it's designed to degrade rapidly after skin penetration compared to ru that has slightly higher [systemic activity]." — r/tressless
Dosing, vehicle, and application practice#
Where people go wrong with both compounds is the vehicle and the dose, not the molecule.
RU58841
- 50 mg/day is the standard sweet spot. 25 mg works for maintenance, 70+ mg is where sides risk climbs steeply.
- Dissolved in a PG/ethanol base (classic Kirkland-style vehicle) or a minoxidil-compatible solvent. Some users split into AM/PM to reduce peak systemic exposure.
- Apply to a dry scalp. Layering directly on top of wet minoxidil increases systemic pickup without adding local effect.
Pyrilutamide
- 0.5% solution, twice daily, is the dosing used in the Kintor trials and what most users replicate.
- Rapid degradation means you actually need the BID schedule — once-daily underdelivers.
- Plays nicely with topical minoxidil and topical fin in the same routine since systemic load is low.
For both: buy from a vendor with third-party HPLC assays. This category is full of underdosed or degraded product, and a bad batch will cost you six months of your scalp's time before you figure out why nothing's working.
Cost, availability, and sourcing reality#
- RU58841 is the older, more widely stocked compound. Per-gram pricing from reputable research-chem vendors has stayed relatively stable; a year of 50 mg/day runs roughly $200-400 depending on vendor and whether you're mixing your own vehicle.
- Pyrilutamide is newer and typically priced higher per effective dose, especially from pre-mixed vendors. Mixing from raw powder narrows the gap considerably.
- Neither is approved as a drug in the US or EU. Both are sold as research chemicals. Legal status and import rules vary — know your jurisdiction before ordering in volume.
Which one to pick#
A simple decision tree that matches what experienced users actually do:
- You're a hard responder with real ground to regrow, and fin/dut+min has plateaued: RU58841 at 50 mg/day. Watch for gyno signs, pull bloods at 8-12 weeks, keep an AI on hand if you're also on AAS.
- You can't tolerate oral 5-AR inhibitors and need a low-sides third agent for maintenance: pyrilutamide 0.5% BID. Cleaner systemically, easier to run indefinitely.
- You're on cycle and want local AR blockade without touching systemic DHT: either works, but pyri is the safer default because AAS already taxes estrogen management. Stacking RU on top of high-aromatizing compounds is where gyno stories happen.
- You're fin-tolerant and want maximum regrowth potential: oral fin + topical min + RU58841 remains the most battle-tested stack in the community.
How to tell if it's working#
Standardized photos, same lighting, same angle, every 30 days. Hair counts in a 1 cm^2 zone if you want to be rigorous. Don't evaluate before month 4 — both compounds go through a shed phase in responders, and the signal lives at month 6+. If you've run either at a proper dose in a proper vehicle for 9 months with zero change on standardized photos, you're a non-responder to that molecule specifically — switch, don't stack more of the same.
Bottom line#
RU58841 hits harder and regrows more; pyrilutamide is cleaner and easier to live with. If you need regrowth and your endocrine system tolerates it, RU is still the heavyweight. If you need a sustainable maintenance lever — especially alongside AAS or a sensitive sides history — pyrilutamide is the smarter long-term pick. Either one, run properly with a real vehicle and honest month-over-month photos, beats a third bottle of minoxidil.