Ostarine (Enobosarm, MK-2866 or GTx-024), CAS number 841205-47-8 is a research chemical that has been insufficiently researched for its effects related to prevention of muscle loss, reduction of body fat and increasing muscle strength. However, it is probably the most well-researched chemical of SARM (selective androgen receptor modulator) class – there are more than 25 papers concerning ostarine. Currently, it has been studied in phase II clinical trials of healthy elderly  as well as cancer patients  with partial successes, and a phase III clinical trial has been planned . However, insufficient research has not prevented adoption of ostarine as a doping substance by athletes, its subsequent incorporation into the list of doping substances as well as research dedicated to detection of ostarine .
It has been identified that ostarine’s mechanism of action is that of selective androgen receptor modulator (SARM), which is different from that of both testosterone and anabolic steroids. SARMs affect muscle androgen receptors more selectively than testosterone and anabolic steroids, and are not metabolized to estrogenic substances like testosterone or some of the anabolic steroids. In the clinically investigated dose (3 mg) of ostarine concretely, it was a rather selective substance, which did not lower endogenous free testosterone significantly, and did not cause measurable prostate growth in men or hair growth in women. However, ostarine lowered level of total testosterone and LDL (“good cholesterol”), in women the level of luteinizing hormone, follicule stimulating hormone, estradiol and sex hormone binding globuline level was lowered by ostarine . On the positive side, ostarine seemed to lower cholesterol and blood triglycerides. In addition, ostarine lowered both blood glucose and insulin, and increased insulin sensitivity. Doses larger than those studied have been used as a doping substance. It is very reasonable to speculate that the increased doses used by doping users are less selective, and testosterone suppression, increased prostate growth and increased hair growth seem more plausible.
According to preliminary research, ostarine does not belong into the group of the drugs that seriously alter metabolism of other drugs or vice versa , yet it is known that it may temporarily heighten the level of liver enzymes, indicating that this substance may be dangerous in combination with liver insufficiency, liver damage or high risk of the latter such as chronic alcoholism.