Context: To review the rationale underlying the banning of hCG and estrogen blockers (antiestrogens, SERM's, aromatase inhibitors) in sports for male and female athletes in the light of gender differences in regulation of reproductive physiology.

Evidence Acquisition: Review of (a) well-controlled clinical studies of exogenous testosterone effects on human muscle size and strength in men and (b) of all available evidence relevant to the effects of hCG and estrogen blockers on blood testosterone in men and women.

Evidence Synthesis: Well-designed placebo-controlled clinical studies in men with suppressed pituitary-testicular axis establish a strong case that, across a wide range from sub to supraphysiological doses, muscle growth and strength is proportional to exogenous testosterone dose and resulting blood testosterone concentrations. In men, there is unequivocal evidence that hCG and estrogen blockers cause consistent and sustained rise in blood testosterone concentrations. In women, although there has been no direct testing of ergogenic or myotrophic properties of exogenous testosterone in healthy women, either hCG or estrogen blockers do not produce any consistent or biologically significant increase blood testosterone concentrations.

Conclusions: In men undergoing potential stimulation of endogenous blood testosterone concentrations, blood testosterone concentration is a reasonable surrogate measure for muscle growth and increased strength in men. Because hCG and estrogen blockers produce marked increase in blood testosterone concentration in men, this provides strong evidence to support the banning of hCG and estrogen blockers in men. In women, however, the negligible effect on blood testosterone suggests that drug-induced performance enhancement by hCG or estrogen blockers are highly unlikely. Furthermore, routine urinary hCG testing in young women risks invasion of privacy by detecting unrecognized pregnancy. These considerations suggest that prohibition of hCG and estrogen blockers should be restricted to men where they are well justified.