The Strange Predicament of RU58841

RU-58841 MezogenRX. 2% Formulation.

In the early 1990s, scientists in France synthesized a new topical anti-androgen called RU58841 (or RU-58841). This product was effective at tackling various androgen related disorders, including hair loss, acne and hirsutism.

Since that time, a few favorable studies have been published that have shown the effectiveness of RU58841 in regrowing hair (in hamsters, humans and mice) at low doses.

In some countries, you can purchase products that contain RU-58841 as an ingredient. The MezogenRX product on the right is from Indonesia and it contains 2% RU-58841 in addition to Minoxidil Sulphate.

RU58841 Antiandrogen for Hair Loss

In the US, you can even buy RU-58841 from Amazon via brands such as Vantanex (in a 5% solution).

However, unlike Minoxidil or Finasteride, the US FDA has not approved the use of RU58841 for treating scalp hair loss. The product cannot be prescribed at pharmacies and is not meant to even be used by humans. RU58841 is classified as a chemical and can be purchased by pharmacists in the US for independent research. Strangely enough, it is sometimes sold on Amazon in various powder and spray versions.

RU58841 Powder.
RU58841 Powder.

It does not seem like the chemical has been approved anywhere in the world to treat hair loss and balding. This has not prevented numerous hair loss sufferers around the world from getting their hands on RU58841 and using it.

Although illegal, this is not surprising to a hair loss sufferer such as myself. People on hair loss forums have tried much crazier things in the past, and will always do so. Internet commerce also makes law enforcement that much harder. The below video is an interesting take on one brand of RU.

Hair Growth Results

You can find dozens of very positive online testimonials regarding RU58841 from reputable and active members on hair loss forums. It should be noted that some of these testimonials may credit RU58841 for positive results, when in fact the person is also using Minoxidil and/or Finasteride and/or Dutasteride. Therefore making it hard to gauge which product is most responsible for the positive results.

Among the more interesting RU58841 related testimonials from active forum members or youtubers include those from: Mr. Antiandrogen1; hellouser; and Swooping. You can also find before and after photos with testimonials on Reddit. Almost all are from men suffering from male pattern baldness and thinning hair. Women rarely seem to take this strong antiandrogen.

RU58841 Side Effects

Topical RU58841 has a very short half-life (1 hr) in comparison to the oral ingestion of Finasteride (6 hrs) and Dutasteride (5 weeks!). Moreover, RU58841 does not inhibit dihydrotestosterone (DHT) production like the latter two hair loss treatment products. These facts seem to suggest that there is minimal chance of any serious or permanent side effects. Anecdotal evidence on the forums seems to support this conclusion. Carcinogenic effects such as cancer are not proven.

However, because many people are buying RU58841 from online sometimes unknown and unverified suppliers, there is no guarantee of any kind of safety. I am not planning to buy RU58841 online because of safety issues. The product is also quite expensive in comparison to Minoxidil or Finasteride. If you really do wish to buy this product, consult a doctor first.


Coming back to the title of this blog post, why do I find RU58841’s predicament strange? The answer is due to the fact that despite a respectable amount of evidence over the past two decades in support of the product’s anti-androgenic capabilities, no company has decided to go through with clinical trials for this product for use as an anti-androgen. This is especially surprising considering that side effects are likely to be minimal to non-existent when RU58841 is taken in low doses.

Perhaps companies do not think that the product is much better than topical Minoxidil? Or because the product cannot be patented, the long-term profitability and monopoly of any new product containing RU58841 is suspect? Even stranger, the research on this product has dried up in recent years. This situation is not true for other well known anti-androgens such as Spironolactone and Flutamide.

History of RU58841

It seems like the original RU58841 was renamed to HMR3841, and then to PSK3841 after a company named ProStrakan acquired rights to it. I assume that the current name is yet again RU58841?! Thanks to commentator “yo” for pointing out that this fact was mentioned in hellouser’s lengthy forum thread that I linked to earlier in this post. More importantly, PSK3841 was analyzed in a 2005 Morgan Stanley report and I am pasting the favorable analysis below:

“ProStrakan’s topical androgen receptor antagonist has completed a Phase IIa proof-of-concept study for alopecia. In this trial, which was not powered for efficacy, there was an observed increase in both new and existing hair growth and the data compared well with historical data for finasteride (marked by Merck as Propecia). We believe the market for this agent is resonably modest – US $100 – 200 million – but that could be of interest to a specialty dermatology company.”

Also, I found details about a human study on PSK3841 that was supposedly done in 2002, but am not sure if it was ever completed. If anyone lives in France, please see if you can contact Dr. Evelyne Guénolé, the primary contact person for that study.

32 thoughts on “The Strange Predicament of RU58841”

  1. I really can’t understand why you discourage using RU (just because companies didn’t find ways to turn it into money). I believe a more practical approach is to find a reputable laboratory that makes it.

    Anyhow, I have two questions:
    1. could you please link to the humans studies with RU?

    2. something I can’t understand about half-life of drugs – does the 6 hours with finasteride (for example) refers only the the free circulating compound in the blood or also to the compounds which are attached to the 5-alpha reductase? and another thing – if the half-life of Dutasteride is 5 weeks, why should it be taken daily (at least according to the studies)?


    1. Hi Ron, as a blog author I cannot encourage this illegal activity!

      I think this one has both human and “mammalian” subjects:

      This one has human ones, but is focusing on acne:

      This one moves human hair to mice:

      Not too much I agree…but I assume that some of the original work from the 1980s and 1990s in France must have been on humans too?

      EDIT: See my update at the end of the post. Apparently, there was a human trial in 2002 in France.

      1. Thanks for the reply!
        Unfortunately didn’t find anything informative about the safety of RU for humans in those studies :(

        The study of Dr Evelyne Guénolé that you mentioned seems great, but I couldn’t find her email anywhere over the internet, only her clinic address…

  2. Very very.. Suspicious indeed. To me its quite obvious that the medical industry has comitted atocities in order to maintain their influx of profits up. And cures for the most devastating diseases have probably been cured 2,3 maybe more decades ago..

    1. The absolute absurdity in your implications has zero founding or reason. Why should anyone invest hundreds of millions of dollars if not to gain something in return? Why would they? Do you think the government would do it? You better be glad they make money off of it because the government wouldn’t give two shits about hair loss if they were in charge of medicine.

  3. Hey Admin!

    Firstly, thanks for this site, I get a lot of valuable information from here!

    I know of RU, never actually research it until now. Apparently, it was previously known as both PSK-3841 & HMR-3841 (please correct me if I’m wrong!), the former discussed in the summary below. I found this info following Hellouser’s RU log which you posted above – some may find it useful and interesting as well.

    “In this trial, which was not powered for efficacy, there was an observed increase in both new and existing hair growth and the data compared well with historical data for finasteride (marked by Merck as Propecia). We believe the market for this agent is resonably modest – US $100 – 200 million – but that could be of interest to a specialty dermatology company.”

    If I understand correctly, despite RU proving its efficacy and its anti-androgen capabilities, future developments were halted because they didn’t believe there was enough money to be made?

    Seems to be what everything boils down to.

    1. Thanks you!! Updated my post at the end. Hellouser’s thread was way too long for me to go through in its entirety:-)

  4. Es lo mismo que opino yo. El admin. está en la misma situación que nosotros con la caída del cabello. Estamos en 2015, recién empezando el año, no me imagino esperar 5 años mas para ver algo en el mercado. Día a día el pelo se me sigue cayendo y afinando. Y quien sabe si salga en el 2020. Realmente patetico.

  5. Y lo peor de todo es que mandas correos a Follica y nunca nadie te responde. Replicel e Histogen parece que copiarían el mismo mail para todos. No se puede estimar cuando puede estar en el mercado te responde. Es una tomada de pelo realmente. Manejan millones. Y las compañias farmaceuticas ni hablar, es todo un negocio económico. Yo la verdad que cada día que pasa tengo menos esperanzas.

  6. Enough of all these basically useless ideas to obtain more hair on our heads. When is Replicel starting it’s Phase II? They need to get the ball moving quicker so we will FINALLY have a real solution to hair loss!!!

  7. Yo escribí a Replicel la semana pasada y no me dijeron en que mes empiezan en Alemania. Y shiseido tampoco. Histogen directamente no contestan. Encima el ensayo va demorar 39 meses!!!! 3 años esperando! yo no lo puedo creer. Alguien sabe algo???? alguna buena noticia para escribir en este blog???

  8. From what I remember from my short research on RU58841, is that it is not very suitable to become an actual product because it is not stable when mixed with the vehicle ( the liquid solution). If you read the instructions for it’s use you will see that people mix a new batch every week or so. Maybe that’s also the reason why the half-life is so small?

  9. Replicel obtuvo 11.8% en promedio y algunos un 19%. Si al repetir inyecciones esto aumenta, estamos en presencia de una “cura”, si esto no aumenta ni va a salir al mercado, así que en 2016 ya sabremos el panorama.

  10. I don’t believe in Replicel at all! The only thing we need it’s a drug to reactivate the hair follicle! And unfortunately it takes time…

  11. si, en 2016 recogen los datos de la phase 2. Igualmente toda la fase dura como 3 años calculo. Si sale bien con las leyes de Japón creo que shiseido puede empezar a comercializarlo. Siempre y cuando sea un resultado importante en porcentaje calculo. En Facebook dice que inician en la primera mitad de 2015 en Alemania creo. Veremos

    1. Es interminable este tema. Yo creo que ninguna empresa tan importante como shiseido se arriesgaría a semejante inversión ni no obtuvieran resultados positivos. Oses que si da buenos resultados en la fase 2 en 2016 ya podrían comercializarlo en japón??? Ojalá que aparte de comercializarlo en japón otros países como el mío ARgentina puedan traerlo hacia acá. Mi país no es riguroso con las leyes.

  12. Y de Histogen???? se sabe cuando empieza en japón???? se decía que ellos incluso podían salir al mercado en japón antes que replicel.

  13. Well I ordered some RU. And the KB solution to mix in it, after reading 6 or so pubmed articles. Most posters on the other forum say it stops shedding but does not regrow without co administration of minox during the day sometime. Currently I have eucapil. Not sure how long it will take to arrive from Kane shop. Right now she’s is about 100 per day. Down from 200 (spike from Zoloft trial – stopped that!)

    1. any updates please it would really be help full? Did eucapil out perform RU? Did you get any regrowth with RU and sides? Whats your experience?

  14. Admin any change of thoughts/mind on RU since you originally posted this piece almost 9 years ago?

    I was waiting for kintor but they seem to be pushing the testing for another year so I doubt it will be released anytime before 2025 … Im contemplating about starting RU in the meantime but concerned by the unknown sides profile. Oral minoxidil only started picking up usage recently although some people has been on if for a decade now. Not sure why RU hasn’t picked up the same pace.

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