Estrogens and androgens are hormones that play critical roles in men's health, regulating not only the reproductive system, but also having important effects on the muscular, skeletal, cardiovascular and central nervous systems. In order for the body to function properly, a balance must exist between estrogens and androgens.

Although the natural hormones have been used for many years, their use has been limited by undesirable estrogenic and androgenic side effects. GTx is developing toremifene, a selective estrogen receptor modulator, and Ostarine™, a selective androgen receptor modulator, which confer many of the benefits of estrogen and testosterone while minimizing their unwanted effects.

Estrogens prevent bone loss and osteoporosis and reduce the risk of skeletal fractures. In aging men, there is a gradual increase in estrogen levels in the blood, which may promote BPH, initiate prostate cancer and cause gynecomastia.

Estrogen	SERM
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Testosterone is the predominant androgen in men. It is important for mental well-being and for masculine characteristics, such as muscle size and strength, bone strength and male pattern hair growth/loss.

Testosterone	SARM
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Testosterone also maintains sexual interest, fertility, erectile function and normal prostate growth. In aging men, there is a gradual decrease in testosterone levels, leading to loss of muscle mass and strength, reduced bone mineralization, resulting in osteoporosis and bone fractures, erectile dysfunction, decreased sexual interest, depression and mood changes.