S23 is undoubtedly one of the strongest SARMs in development right now. S23 is currently under development for potential use as a male hormonal contraceptive.
It is still in the preclinical stage of development, meaning it has only been tested on animals, not humans.
S23 was created by modifying the structure of an older and less efficacious SARM called C-6 by changing the para-nitro group of C-6 to a cyano group. Pharmacokinetic studies showed that C-6 is 76% orally bioavailable, and by swapping the para-nitro group for a cyano group, S23 is able to achieve 96% oral bioavailability. This means that S23 can be administered orally, as opposed to requiring injections to achieve maximal blood serum concentration levels, which is obviously advantageous when it comes to ease of use and application.
The preclinical data revealed that S23 is the most suppressive SARM in development and resulted in infertility in all rats treated. Expectedly, this raised interest in its potential clinical applications as a form of male birth control.
S23 has become increasingly popular in the recreational bodybuilding community for its potent muscle building and body recomposition effects. Recreational users are quick to label S23 as a more potent alternative to S4 (S-4), without the night vision side effect. S23 has also shown to decrease prostate size in studies, which is the opposite of a very common negative side effect of anabolic steroids (enlargement of the prostate). This data is commonly misinterpreted though, as all SARMs will prevent prostate hypertrophy in a dose dependent manner, and this is specifically referred to in the study.
Dosages of 10 – 30 mg per day are commonly used in a recreational context for muscle building purposes. There is no established therapeutic dosage of S23. Anecdotally, S23 is reported to show diminishing returns at dosages above 30 mg per day. The mean terminal half-life of S23 in rats is 11.9 hours. The half-life of S23 in humans is unknown and would require a clinical study to determine it.
Androgen Receptor Binding Affinity
S23 has a very high binding affinity for the androgen receptor (AR) with a Ki of ∼1.7 nM. Ki is a dissociation equilibrium constant defined kinetically as the ratio of rate constants koff/kon for the binding of the substrate to the androgen receptor. In lay man’s terms, the lower the Ki value, the higher the binding affinity for the androgen recptor. To put this in perspective, RAD-140 (RAD140) has a Ki value of 7 nM. S23 has a binding affinity over four times higher than RAD140, which was already considered impressive.
The binding affinity of Testosterone and DHT remains unclear as each study seems to render significantly different values but testosterone has a Ki value of roughly 40 nM. The only SARM in development that is reported to have a formidable binding affinity to S23 is LGD-4033, which has a Ki of ∼1 nM. However, due to the poor oral bioavailability of LGD-4033, oral S23 will be much more potent when compared mg to mg.
“S23 gives very similar results to trenbolone. I notice that if I use too high of a dosage of S23, my metabolism goes so fast that I start to lose weight because I can’t eat enough. With S23, it’s important to match the dosage to the number of calories eaten.
With oral, I’ve gone up to 100mg/day. With injectable I’ve gone up to 50mg/day. The benefits of 50mg S23 injectable were similar to 100mg oral. 5-10 mg/day is the dosage I recommend for women.
I recommend cycling S23 because it is so suppressive of natural testosterone production. I notice that I experience testicular atrophy as I go up in dosage. When this side effect occurs, I use HCG to bring my testicles back to normal size.”
- Dr Tony Huge
“S23 was the second SARM I experimented using high dosages with. S23 gives very similar results to the steroid trenbolone; incredible fat loss, mental energy, focus, and strength. My training was great when using S23. I noticed a great performance benefit.
S23 is my favourite SARM for women. Women get extreme results in both fat loss and muscle. I recommend 5-10mg/day for women.
For men I recommend 20-40mg/day. I’ve personally experimented with dosages as high as 120mg/day. I noticed the benefits started to taper off around 80-100mg/day.”
- Coach Trevor
