Acyline suppresses LH and FSH, which are hormones made by the pituitary gland, thus blocking the signal from the brain that causes the testes to make testosterone. Therefore, Acyline blocks testosterone production. In preliminary studies, a single injection of Acyline reversibly lowered the FSH, LH and testosterone levels in the blood for approximately 15 days. Prolonged low levels of LH and FSH cause suppression of sperm production in normal men. However, men may experience some side effects from the low levels of testosterone caused by acyline, thus exogenous testosterone is required to sustain normal male androgen and organ effects without suppressing spermatogenesis. This combination of drugs is a promising male contraceptive regimen. In addition, millions of older men are using testosterone replacement to treat male "andropause"; low level testosterone associated with aging. However, the effect of testosterone on the prostate is unknown. Studies examining the effect of testosterone on the prostate are needed.