Non-Steroidal Anabolics: S-4
S-4 is a derivative of the androgen receptor antagonist, bicalutamide. Modification of the structure imparted agonist activity to the core bicalutamide structure. This SARM is currently in clinical development under the name Ostarine. To date, this is the only SARM that supposedly has reached the black market. The product being sold has not been tested to prove that it is, in fact, S-4. It has been reported to be effective at doses of 50 to 150 mg per day. This is much higher than the dose of S-4 being used in clinical trials, 3 mg per day. Either what is being sold on the black market is S-4 or the individuals using it are taking a mega-dose. Even so, the black-market product is reported to not produce large gains in muscle mass but is reported to result in strength gains and a loss of fat mass. Additionally, a strange side effect of blurred vision is reported with the use of the black market product. This side effect is similar to clomiphene and suggests that the black market product may in fact contain clomiphene as one of, if not the sole component.
The real S-4 has about a 3-fold selectivity for skeletal muscle compared to the prostate. The fact that this molecule has low androgenic activity and no conversion to estradiol suggests that it may result in reduced libido. Larger doses, beyond those where selectivity has been demonstrated, will likely result in greater androgenic effects.
It may be difficult to see how this SARM resembles androgens, but the flexibility of the structure allows to assume a conformation that is favorable for androgen receptor binding.
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