Is RU58841 Safe? An Honest Answer After Four Years of Using It

If you're reading this, you've probably already looked into RU58841. You've seen the before and after photos, read the Reddit threads, maybe watched a few videos. Now you're stuck on the question everyone gets stuck on. Is RU58841 safe?

It's the right question. I asked it myself before I started, over four years ago. Here's the honest answer. Not the one that makes the easiest sale. The one I'd want if I were you.

The short version: RU58841 isn't approved as a medicine anywhere. That's a fact. But not approved and dangerous are two very different things. The biggest risk usually isn't RU58841 itself. It's buying rubbish from a seller who never tested it.

This isn't medical advice. RU58841 is not a licensed medicine in the UK.

Why RU58841 isn't approved

This is the first thing people bring up, so let's deal with it properly.

RU58841 was made by Roussel Uclaf, a French drug company. The first paper on it came out in 1994. Their own scientists called it "a candidate of choice" for acne, male pattern hair loss and unwanted body hair in women (Battmann 1994).

So why didn't it reach the shelves? Nobody outside the companies involved really knows. The company went through mergers, and development quietly stopped. No official reason was ever published.

Here's the part most people miss. Getting a drug approved costs a fortune and takes years. Nobody owns RU58841 now. No company will spend that kind of money on something anyone can make the day it's approved.

Not approved doesn't mean it doesn't work. And it doesn't mean someone tested it and found it dangerous. It means nobody finished the process.

The full story: What Is RU58841?

What the research actually shows

Here's what the studies found, in plain English.

• It works where you put it. In hamsters, a tiny amount on the skin had a strong effect there, with no effect on testosterone levels (Battmann 1994). On hamster ears, the treated ear's oil glands shrank by up to 60% while the untreated ear didn't change (Matias 1995).
• The effect wore off when they stopped. The hamster glands went back to normal within 4 weeks of stopping (Matias 1995).
• Blood hormones didn't change in rats. Testosterone and DHT stayed the same, and unlike finasteride it didn't shrink the prostate (Ye 1997).
• The body breaks it down in a way that keeps it local. In rats it barely turned into the by product that acts across the body, which the researchers linked to it working locally (Cousty Berlin 1994).
• In monkeys that go bald like men, no effects on the rest of the body were detected (Pan 1998).
• In men, some of it does reach the blood. A 2026 study put one dose on the scalps of six men. RU58841 showed up in their blood afterwards. Their steroid hormone profile didn't change (Okutan 2026).

So here's the honest line. RU works at the scalp. It doesn't lower your DHT. It isn't invisible to the rest of your body either.

Can anyone promise any treatment is safe for everyone? No. But "it's not approved, so it's dangerous" doesn't stand up. Not approved doesn't mean it doesn't work.

How well does each one work?

Safety only matters if the thing works. So first, how well does each option actually work? Here are the real numbers from the studies, each one linked so you can check it. Every study measured things a bit differently, so read each line on its own.

• RU58841 on the scalp: strong. In bald monkeys, RU58841 5% raised growing follicles by 103% and turned 26% of thin hairs into thick ones. The finasteride pill got 88% and 12% in the same study, and RU did it with no hormone change. On real balding human scalp grown on mice, 28% of follicles started a new growth cycle with RU, against 7% without it. (Uno monkey study, not on PubMed; same team: Pan 1998, De Brouwer 1997)
• Finasteride pill: strong. 1,553 men. After two years, men on finasteride had 138 more hairs in a one inch circle on the crown than men on a dummy pill, who kept losing hair. It cuts the DHT in your blood by about 71%, which is why some men get side effects. (Kaufman 1998, Drake 1999)
• Topical finasteride: good. 458 men, 24 weeks. Hair count up 20.2 hairs, against 6.7 on a dummy spray. About the same as the pill. Blood DHT still dropped 34.5% (the pill: 55.6%). (Piraccini 2022)
• Minoxidil 5%: good. 393 men, 48 weeks. 5% beat the dummy and grew 45% more hair than 2%. It doesn't touch DHT, so it works best next to a DHT blocker. (Olsen 2002)

Short version: stop the DHT first, then grow the hair. That's a DHT blocker plus minoxidil, with a dermastamp once a week. RUstim+ does the first two in one bottle.

RU58841 safety vs finasteride safety

Finasteride is approved. It's had big trials. It's prescribed everywhere. And:

• It cuts DHT in your blood by about 71%, all over your body, not just the scalp (Drake 1999).
• A review of 12 trials found it raises the risk of erection problems (Mella 2010).
• Some men report side effects that carry on after stopping (Irwig 2011).

RU58841, by contrast, goes on the scalp and, in the studies, didn't lower blood DHT. The most common complaint is a dry or itchy scalp, usually from the alcohol in the liquid. A small number of users report a racing heart. That's covered in our side effects guide.

I'm not claiming RU58841 is "proven safe". I'm saying an approved drug with documented side effects isn't automatically safer than an unapproved one that works at the scalp. It deserves more thought than checking whether a box has been ticked.

Side by side: RU58841 vs Finasteride.

The real risk: what's actually in the bottle

This is where the conversation needs to go.

RU58841 isn't a regulated medicine. Anyone can make it, bottle it and sell it online. Nobody checks the purity, the strength or what else is in there. That's where things get dangerous.

What can go wrong with untested RU58841

• Leftovers from bad manufacturing. Solvents and by products that were never part of the research, and could irritate your skin or worse.
• The wrong strength. Too little and you're wasting money. Too much and you're raising the odds of side effects for nothing.
• Broken down product. Stored badly, it degrades. You end up putting the breakdown products on your head instead of RU.
• Fillers. Some sellers cut it to make more money.

When someone has a bad time with RU58841, a bad product is a very likely explanation.

What third party testing means

Third party testing means an independent lab, not the seller, checks what's in the product. Our RU58841 has been lab tested by Janoshik Analytical, an independent lab.

A proper test tells you two things:

• Purity. It's actually RU58841, at the purity stated, without significant contamination.
• Identity. It's the compound it says it is, not something else.

Our certificate shows RU58841 at 98% purity or more, and you can check it on Janoshik's own website with the verification key.

If a seller can't show you an independent lab test for what you're buying, don't buy it. Simple as that.

Four years of personal use: what I've experienced

I started RUrestore because I use this myself. That's not a marketing line. It's why the company exists.

I tried finasteride for about six to eight weeks and got the side effects that made me stop. Lower libido, brain fog, not feeling like myself. After my transplant I needed something to protect my hair without that. RU58841 was it.

Over four years of daily use:

• No sexual side effects.
• No brain fog, no mood changes.
• Now and then a dry scalp. Easy to manage.
• My hair has come back and stayed.

That's one man's experience. I know that. It isn't a clinical trial.

Who should not use RU58841

• Women who are pregnant, breastfeeding or trying to get pregnant.
• Anyone under 18.
• Anyone with broken, sore or infected skin on the scalp.
• Anyone with a heart condition, given the reports of a racing heart. Speak to your doctor first.
• Anyone on hormone treatment. Speak to your doctor first.

How to use RU58841 as safely as possible

1. Only buy from sellers with an independent lab test. Ask for it. No test, walk away.
2. Check the purity. You want 98% or more.
3. Store it in a cool cupboard. Away from heat and sunlight.
4. Stick to the standard dose. 1ml of a 5% solution, once a day. Morning or night, any time, as long as it's every day.
5. Patch test first. A small area for a few days before you go all over.
6. Listen to your body. Anything beyond a mildly itchy scalp, stop and see if it settles. If it doesn't, see your GP.

Full routine: How To Use RU58841. Dose and strength: RU58841 Dosage Guide.

The bottom line on RU58841 safety

The research shows a DHT blocker that works where you put it, and didn't lower blood DHT in the studies. Some does reach the blood in people.

For those who choose to use it, and I'm one of them, the risk you can control is the product. Tested RU58841 from someone who shows you the certificate is a different thing from mystery powder off the internet. That's the difference that matters.

RUstim+ (RU58841 and minoxidil) or RU58841 5% on its own. Our RU58841 has been lab tested.

Frequently asked questions

Is RU58841 a licensed medicine in the UK?

No. It isn't licensed by the MHRA or approved by the FDA. No doctor will prescribe it and no pharmacy stocks it. Not approved doesn't mean it doesn't work.

How do I check a seller's lab test?

Ask for the certificate. Check the lab's name, the date, the purity and the compound tested. Janoshik certificates come with a verification key you can enter on Janoshik's website to make sure it's real.

Is RU58841 safe for women?

It shouldn't be used by women who are pregnant, breastfeeding or trying to get pregnant. Any woman thinking about it should speak to a doctor first.

Should I tell my GP I'm using it?

Yes. It's always worth your GP knowing what you put on your body, especially if you have a health condition or take other medicines.

What's the biggest safety risk with RU58841?

An untested product. You don't know the purity, the strength or what else is in it. Buy only from someone who shows you an independent lab test.

Sources

1. Battmann and colleagues (1994). J Steroid Biochem Mol Biol. Strong effect where applied on hamster skin, no effect on testosterone levels. PubMed 8136306
2. Cousty Berlin and colleagues (1994). J Steroid Biochem Mol Biol. How rats break down RU58841, and why it works locally. PubMed 7947350
3. Matias and Gaillard (1995). Ann N Y Acad Sci. Treated hamster ear changed, untreated ear didn't, effect gone within 4 weeks of stopping. PubMed 7625751
4. Ye and colleagues (1997). Skin Pharmacol. No change in rat blood testosterone or DHT, prostate unaffected. PubMed 9449168
5. Pan and colleagues (1998). Endocrine. Hair regrowth in bald macaques with no effects on the rest of the body detected. PubMed 9798729
6. Okutan and colleagues (2026). Biomed Chromatogr. RU58841 found in the blood of six men after one scalp dose, steroid profile unchanged. PubMed 42615108
7. Drake and colleagues (1999). J Am Acad Dermatol. Finasteride 1mg cut blood DHT by about 71%. PubMed 10495374
8. Mella and colleagues (2010). Arch Dermatol. Review of finasteride trials. PubMed 20956649
9. Irwig and Kolukula (2011). J Sex Med. Sexual side effects that lasted after stopping finasteride. PubMed 21418145
10. Uno and colleagues. Conference abstract, Wisconsin Regional Primate Research Center. Follicular regrowth with 5α reductase inhibitor (finasteride) or androgen receptor blocker (RU58841) in the bald scalp of the stumptailed macaque. Not on PubMed. Same team's published RU58841 paper: Pan 1998, Endocrine
11. De Brouwer and colleagues (1997). Br J Dermatol. Balding human scalp on mice: 28% of follicles started a new growth cycle on RU58841, 7% without. PubMed 9415227
12. Kaufman and colleagues (1998). J Am Acad Dermatol. 1,553 men: finasteride 1mg gave 138 more hairs than a dummy pill after two years. PubMed 9777765
13. Piraccini and colleagues (2022). J Eur Acad Dermatol Venereol. Topical finasteride in 458 men. PubMed 34634163
14. Olsen and colleagues (2002). J Am Acad Dermatol. 5% minoxidil grew 45% more hair than 2%. PubMed 12196747