RU58841 side effects ?

RU58841 is applied to the scalp, where it is taken up by the hair follicles. In theory, it could then enter the bloodstream and affect other parts of the body. Studies in monkeys did not detect any systemic RU58841 side effects from topical applications (1). However, some individuals who have tried RU58841 claim they experienced systemic RU58841 side effects. The side effects reported include skin irritation, decreased libido, erectile dysfunction, strange sensations, red eyes, blurred vision, nausea, aches and pains, dizziness, and headaches (2).

In Theory

The skin irritation seems to be entirely due to the carrier used to dissolve the RU58842; some users use too much ethanol or other innately skin-toxic substances for this purpose (propylene glycol…). Individuals who use other carriers do not report any skin irritation. It is unclear if the other RU58841 side effects are actually due to the RU58841 or are just a placebo effect. As an androgen blocker, it is theoretically possible for systemic RU58841 to cause reduced libido and erectile dysfunction. Nilutamide, an androgen blocker used orally to treat prostrate cancer, is reported to occasionally cause blurred vision, dizziness, and aches and pains (3).

Mathematical Model

However, a mathematical model of the breakdown of RU58841 clearly demonstrates that even if it is absorbed efficiently into the bloodstream, its active metabolites can never achieve a dose high enough to cause any anti-androgenic side effects (4). The model is based on knowledge about the breakdown of RU58841. After application to the scalp, the original RU58841 molecule has a half-life of only around 1 hour. It primarily breaks down into RU59416, a compound that only weakly binds to androgen receptors. Around 1% of RU58841 breaks down into RU56279, also called cyanonilutamide. Cyanonilutamide has powerful anti-androgenic effects. It is similar in structure to anti-adrogenic drugs used to treat prostate cancer, and if it were to enter the body in a high enough dose, it would be expected to cause side effects similar to those reported for nilutamide (3).


Cyanonilutamide has a half-life of about 20 hours in the body. This long half-life has caused some to suggest that regular use of RU58841 can cause cyanonilutamide to build up in the body over time, eventually reaching a dose that causes side effects. However, the mathematical model mentioned above has proven this does not happen. The formula to estimate the decay of a drug over time is based on the basic mathematical formula for exponential decay:

ru58841 side effects

This basic formula needs to be modified to take into account application of a new dose of RU58841 each day:

ru58841 side effects 2

If you begin calculating from the day of the very first application of RU58841

ru58841 side effects 3

this formula is simplified to a geometric series :

ru58841 side effects 4

Does Not Build Up

Assuming a daily dose of 100 mg of RU58841 is applied, and also assuming that all of the cyanonilutamide produced enters the bloodstream (unlikely), a dose of 1 mg of cyanonilutamide is being taken each day. Rounding the 20 hour half-life of cyanonilutamide up to 24 hours to simplify the calculations and plugging these numbers, you end up with:

ru58841 side effects 5

This formula shows us that the amount of cyanonilutamide in the body cannot go over 2 mg, even if you use RU58841 daily for years.

Too Low

Two mg of cyanonilutamide is a miniscule dose that is almost certainly incapable of causing any noticeable side effects. Therapeutic doses of other androgen blockers that are given orally are in the 150 to 750 mg range. However, a 2 mg dose isn’t going to block very many androgen receptors. It therefore seems very unlikely that any of the RU58841 side effects are actually caused by the RU58841.


(1) Endocrine. 1998 Aug;9(1):39-43. Evaluation of RU58841 as an anti-androgen in prostate PC3 cells and a topical anti-alopecia agent in the bald scalp of stumptailed macaques.
(2) Reported on various hair-loss forums [,,,]
(4) Model developed by a forum member []

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