MGA is a weak partial agonist of the androgen receptor (AR). It has been reported to bind to this receptor with 5% of the affinity of the anabolic steroid metribolone. Despite its weak intrinsic activity at the AR, at clinical doses in humans, MGA appears to behave, for all intents and purposes, purely as an antiandrogen. This is based on the fact that no virilizing side effects have been observed with the use of MGA in patients of either sex at dosages up to as high as 1,600 mg per day, the highest that has been assessed. Furthermore, MGA produces detectable androgenic effects in animals only at a dose that is the equivalent of approximately 200 times that typically used for the treatment of prostate cancer in men. However, the medication does have moderate androgenic effects on serum lipids in humans, causing a significant reduction of HDL cholesterol and cholesterol levels and no change in triglyceride levels at a dosage of only 5 mg/day. Conversely, MGA does not decrease SHBG levels. The weak but significant androgenic activity of MGA may serve to limit its clinical effectiveness in the treatment of prostate cancer.