RAD-150 belongs to class of compounds known as “anabolic esters” due to esterification during chemical synthesis. Historically, esterification of testosterone was pursued in order to permit more stable serum testosterone levels. Now, synthetic chemists are applying these insights to SARM research and development to achieve a similar goal: more stable and durable serum SARM levels.
Fig. 1. Timeline of half-lives for three different testosterone esters. Each ester has an increased half-life compared to the one before it, and all three have better stability than non-esterified testosterone, which has a very short half-life of only 10 to 100 minutes. Adapted from Nieschlag et al. Andrology: Male Reproductive Health and Dysfunction. Springer Science (2010).
Superficially, it seems reasonable that employing bioidentical testosterone would be the most rational approach increase serum testosterone. However, this is not the case, mainly due to the issue of half-life (ie. stability). Unmodified testosterone has a very short half-life, resulting in spikes which are associated with undesirable mood swings and other consequences. The downsides and adverse effects from testosterone spikes that result from using non-esterified anabolic agents have always prevented their widespread adoption and acceptance.
To overcome this issue, scientist began to modify testosterone to make it more stable in the body. The chemical synthesis process by which any variety of ester groups are attached to carbon-based molecule is call esterification, and it has been a common functional modification to anabolic compounds since the discovery of the original androgens and estrogens. Esterification can serve to enhance stability (chemical or metabolic), change bioavailability, increase absorption, among other pharmacological goals.