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RU-58841 , safer alternative to finasteride?


Are you battling with hair loss and searching for a novel solution that has genuine results? Perhaps you have tried various treatments and products but have yet to notice any substantial improvement. If so, you may have heard of the cryptically named RU-58841. Is this a promising new treatment suitable for you? What even is it? How does it work? Is it safe? We will dive deep into RU-58841 so you can find out if it is the holy grail of hair regrowth or not.


The science of hair loss

Baldness. Hair loss. Whatever you call it, it’s a distressing condition and for some men and women, seen to be an inevitable fact of life and ageing. You’ve probably heard the commonly held view that if your mother’s father was bald, you will end up bald too. So, it’s only natural to look at older relatives and wonder when our hairlines will start creeping back. Sadly, we can’t exactly alter our genes…yet!


While genetics are important, with some research suggesting that up to 80% of early and late-onset hair loss in men is due to genetic factors, this doesn’t tell the whole story.


Another major factor is hormones, namely androgens like testosterone. And hormones we can work with! In fact, hormones can activate genes responsible for pattern balding.


Read on to find out more about how hormones, hair loss and how drugs like RU-58841 are designed to disrupt this process.


How hormones affect hair loss.

Androgens, sex hormones such as testosterone and dihydrotestosterone (DHT) play a major role in the biological process behind pattern balding. Our hair follicles have androgen receptors which these hormones bind to, leading to the activation of genes which shorten the anagen (growth) cycle of the hairs.


This process of follicular miniaturisation constricts the hair follicle and causes thicker, pigmented hairs to be replaced by thinner, shorter, fragile, depigmented ones. As this process takes place over the crown, temples and hairline, the hair thins and falls in a typical pattern, hence the term ‘pattern baldness’.


Many hair loss treatments are targeted at stopping or blocking this hormonal process. finasteride, dutasteride and pyrilutamide are examples of drugs that are designed to block the process. Another less well-known (though experimental) treatment is RU-58411. In this article, we will look at RU-58411 and the following:


  • How does it work?
  • What makes it different from other treatments like finasteride?
  • What do trials and studies on RU-58841 say?
  • Does RU-58841 work and is it safe?
  • What do users of RU-58841 say about it?
  • How soon will RU-58841 show results?
  • How to use RU-58841 – dose and frequency.
  • What are the side effects of RU-58841?
  • How stable is RU-58841?



RU-58841 – What is it?

RU-58841 is the alphanumeric name of an experimental compound developed by a French pharmaceutical company called Roussel Uclaf (Hence RU). It is from a class of drugs called non-steroidal anti-androgens (NSAAs). It is also known as PSK-3841 or HMR-3841. RU-58841 was initially developed as a drug for acne vulgaris and hirsutism, which like baldness, are both conditions characterised by excessive androgen production or sensitivity.


Other examples of NSAA drugs include bicalutamide, an established treatment for prostate cancer that blocks testosterone to prevent the proliferation of malignant cells.


How does it work?

As an anti-androgen, RU-58841 acts by blocking the androgen receptors in the area it is applied. When applied topically to the scalp, RU-58841 acts on the follicle, binding to the androgen receptor with an equivalent affinity to testosterone. This blocks DHT and testosterone from binding to the androgen receptor and as a result, stops the activation of genes that shorten the anagen phase.


Anti-androgens vs 5-Alpha-Reductase blockers: what is the difference?

The theory behind an androgen blocker like RU-58841 is that it could lead to reduced side effects compared to other commonly available and conventional hair loss treatments. This is because of a subtle difference in the mechanism of action. This hasn’t been proven in clinical studies, but theoretically means that people who have struggled with 5-AR blockers could find medications like RU-58841 a possible treatment option.


Finasteride and Dutasteride are both 5-AR blockers and widely used hair loss treatments. 5-AR is an enzyme that converts testosterone to DHT. By preventing or reducing this process, 5-AR blockers reduce the levels of DHT, and this stops the chain reaction that leads to the shortening of the anagen phase and subsequent hair loss. The issue with 5-AR blockers that some, but not all users experience, is the occurrence of sexual side effects like difficulty getting an erection or delayed ejaculation. Why? Though blocking of DHT conversion in the scalp is desirable, when it occurs in other areas of the body, it can have unintended effects.


RU-58841 works one step along the process. Instead of blocking the conversion of testosterone to DHT, RU does not affect hormone levels directly. Instead, it prevents DHT from binding to the androgen receptors and prevents negative effects on the follicular growth cycle.


Designed for topical application to the scalp, RU-58841 is intended to locally block androgen receptors without systematically affecting other hormonal processes and theoretically leading to reduced sexual side effects. In theory, it sounds good, but what does the research say?


What do trials and studies on RU-58841 show?

RU-58841 was previously under investigation by the manufacturer, ProStrakan, a Scottish Pharmaceutical company (Hence the other alphanumeric name PSK-3841). Phase I and II trials were completed. This means pre-clinical studies involving animals and small human trials examining dosing and safety were done. Unfortunately, no data from these trials was published and clinical trials have halted since 2007.


However, there have been several encouraging animal studies with published data on RU-58841. Though it is difficult to extract results directly from animal studies to make conclusions about safety or effectiveness in human patients, it does give us some information to work from.


In a preclinical study, skin from the scalp of balding male patients was grafted onto mice to test the efficacy of RU-58841 vs a control (ethanol). The mice treated with RU-58841 had a slightly higher number of hairs and four times as many hairs initiated a second growth cycle. Additionally, a statistically significant number of hairs demonstrated a higher value for linear hair growth rate, suggesting that the drug lengthened the anagen phase when compared to a control. This is an encouraging finding which supports the efficacy of RU-58841.


In a primate study, the macaque scalp was used as a model for the study of human androgenetic alopecia. Researchers applied 0.5 mL of 5% RU58841 dissolved in propylene glycol, isopropyl alcohol, isopropyl myristate and distilled water to the frontal bald scalp of four adult stump-tailed macaques once daily for 5 months. After biopsies were taken for analysis, the population of anagen follicles was greatly increased and that of telogen follicles was reduced compared to the beginning of treatment. This suggests that the growth phase of the follicle was boosted, and the resting phase was shortened. Additionally, the researchers did not note any systemic effects in the animal subjects.


This last finding agreed with another study on RU-58841 which reported that “unprecedented selectivity with respect to systemic effects suggest that this compound is a candidate of choice for the local treatment of androgen-dependent skin disorders such as acne, androgenetic alopecia and hirsutism.”



Does RU-58841 work and is it safe?

There is a dearth of direct human research into RU-58841 as it is not a mainstream or approved treatment for pattern hair loss. However, we can look at similar treatments with a similar mechanism of action to get a better idea of whether RU-58841 is a safe treatment option.


We can also look at the results from another topical NSAA like RU-58841 such as pyrilutamide. Pyrilutamide is currently undergoing trials in male and female patients in the United States and China. The manufacturer, Kintor, completed a phase II trial in 2021 and reported that efficacy and safety endpoints were acceptably achieved.


Some data from this trial was leaked last year.


In this leak, we can see the drug was tested in two concentrations: one group of 27 patients received 0.25% twice daily, while another group of 30 received 0.5% twice daily (BID). A placebo was administered to 19 people.


The total area hair count (TAHC) was measured both before and after the intervention. In the region studied, research participants in the 0.5% group had an average of 22.73 more hairs after treatment than before, while those in the 0.25% group had 14.75 more hairs after treatment.


As the mechanism of action of RU-58841 is the same as Pyrilutamide, this could indicate that its efficacy as a hair loss treatment could be similar. However, it is important to note that RU-58841 remains in research compound status, it is not approved anywhere in the word as a therapeutic option for hair loss.


A in China and will involve more than 400 patients which may  provide a better source of information about whether NSAAs are safe and efficacious as a treatment for hair loss.


What do users of RU-58841 say?

RU-58841 can be bought online as a ‘grey market’ compound and is used by men and women with pattern baldness as an unofficial, unprescribed treatment. As a result, there is quite a lot of information out there from these users. Though anecdotal evidence is no substitute for well-designed and unbiased clinical trials, it is worth noting the positive response from users in online forums such as r/tressless on Reddit. The hair loss and regrowth community is highly active online and heavily invested in the grassroots adoption of novel treatments. We would advise discussing starting any new medication with a professional such as your physician or dermatologist though it is encouraging to see that many users report good results with RU-58841 on threads such as this one.


How soon can you see the results with RU-58841?

Because there aren’t any clinical trials, we’ve looked at hair loss forums and online communities to see what users of RU-58841 say. Again, it’s important to note that this is anecdotal evidence, which is not a substitute for clinical trials conducted by professional researchers.


However, users do report positive results a slowing down of hair loss and around half of them reduction of hair loss within a year. Many users with the most positive results seem to combine RU-58841 with a non-topical treatment such as oral minoxidil.


In a trial of pyrilutamide, a similar drug from the same class, researchers noted positive changes within 6 months in a small scale phase 2 clinical trial. RU-58841 could therefore work in a similar timescale though this is a tentative conclusion.


How to use RU-58841 – dose, frequency and application.


There are no standardised or approved dosing regimens for RU-58441 as it has not been extensively studied in humans. However, online hair loss communities and websites often quote a starting dose of 50mg/day topically. Most solutions are available in a concentration of 50mg/ml, meaning that 1 ml should be applied to the areas with hair loss once per day. Higher doses of 75-100mg per day may be required if results are not seen within the first several months of use. As RU-58841 is a research compound, not designed for human consumption, we do not endorse it as a treatment for hair loss.


What are the side effects of RU-58841?

As we mentioned above, RU-58841 applied topically has been reported to show few systemic effects and is selective for local androgen receptors. This doesn’t mean that there are no side effects.


RU-58841 is a prodrug. What this means is that it is metabolised and converted into a more active form once it is in the body. RU-58841 is metabolised into a compound known as Cyanonilutamide, which has been shown to have very strong anti-androgenic effects. This could mean that if a small amount of cyanonilutamide were to be absorbed from the scalp into the bloodstream, users could potentially experience effects such as delayed ejaculation, reduced libido or erectile dysfunction. Indeed, a significant proportion of RU-58841 users have reported chest pain and sexual side effects on online forums.



How stable is RU-58841

RU-58841 powder is stable, with manufacturers reporting stability tests with no significant degradation after 24 months at room temperature. RU solution in absence of water has been reported to be stable for several months at room temperature. It is important to prepare the solution without water as the cyanide group (-C≡N) is less stable in presence of water.  


RU-58841: to sum up

Hormones and genetics play important roles in pattern hair loss. RU-58841 is a drug designed to target the hormonal factors behind hair loss, working as a non-steroidal anti-androgen. Intended to act locally in the scalp to block testosterone and DHT-mediated follicular miniaturization, RU-58841 has the potential to slow hair loss and promote regrowth while potentially displaying fewer side effects than 5AR blockers like dutasteride and finasteride, though there is a lack of direct clinical evidence.


Unfortunately, no human clinical trials have looked at the role of RU-58841 in reducing hair loss. We can look at a combination of animal studies, anecdotal evidence, as well as studies of drugs with the same mechanism of action to say that RU-58841 could be a treatment option. However, the bottom line is that as this is a research compound, there simply isn’t enough information available to recommend its safety or effectiveness. With other NSAAs being researched, we would advise waiting for information when the data is published.

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