Selective androgen receptor modulator

Comparison to testosterone

Currently used androgens for male hormone replacement therapy are typically injectable or skin delivery formulations of testosterone or testosterone esters. Injectable forms of testosterone esters (such as testosterone enanthate, propionate, or cypionate) produce undesirable fluctuations in testosterone blood levels, with overly high levels shortly after injection and overly low afterward. Skin patches do provide a better blood level profile of testosterone, but skin irritation and daily application still limit their usefulness.

SARMs provide the opportunity to design molecules that can be delivered orally, but that selectively target the androgen receptors in different tissues differently. The goal of research in this area is to allow a customized response: Tissues that are the target of the therapy will respond as they would to testosterone; other tissues where undesirable side-effects are produced will not.

None of the SARMs yet developed are truly selective for anabolic effects in muscle or bone tissues without producing any androgenic effects in tissues such as the prostate gland, however several non-steroidal androgens show a ratio of anabolic to androgenic effects of greater than 3:1 and up to as much as 90:1 (RAD-140), compared to testosterone, which has a ratio of 1:1.

This suggests that, while SARMs are likely to show some virilizing effects when used at high doses (e.g., use by bodybuilders), at lower therapeutic doses they may well be effectively selective for anabolic effects, which will be important if SARMs are to have clinical application in the treatment of osteoporosis in women. One substantial advantage of even the first-generation SARMs developed to date is that they are all orally active without causing liver damage, whereas most anabolic steroids are not active orally and must be injected, and those anabolic steroids that are orally active tend to cause dose-dependent liver damage, which can become life-threatening with excessive use. Research is continuing into more potent and selective SARMs, as well as optimising characteristics such as oral bioavailability and increased half-life in vivo, and seeing as the first tissue-selective SARMs were only demonstrated in 2003, the compounds tested so far represent only the first generation of SARMs and future development may produce more selective agents compared to those available at present.

Selectivity in men

For example, if the target is bone growth in elderly men with osteopenia or osteoporosis, but with no overt signs of hypogonadism, a SARM targeting bone and muscle tissue but with lesser activity on the prostate or testes would be more desirable.

Selectivity in women

A SARM for women would ideally stimulate bone retention, or libido and other sexual function that androgens can influence, without negative side-effects such as development of male gender characteristics (virilization), increased LDL/HDL ratios, liver dysfunction, and so forth.

In clinical testing

Pre-clinical

Abandoned drug candidates

Availability

In 2013, some supplement companies began selling various SARMs as supplements, in purported violation of both the Food and Drug Administration's Dietary Supplement Health and Education Act of 1994 (DSHEA) and the intellectual property rights of the patent holders of the compounds.

The controversy reached mainstream media when the quarterback of the Florida Gators, Will Grier, allegedly tested positive for LGD-4033, a claim that the University of Florida denies. The news increased online sales of the compound.

On March 25, 2017 Joakim Noah was banned for twenty games by the NBA for testing positive for Selective Androgen Receptor Modulator LGD-4033.