Epidemiological studies hint at a beneficial influence of endogenous circulating testosterone (T), or its metabolite dihydrotestosterone (DHT),such that men with lower concentrations of T or DHT appear to have poorer health outcomes including frailty, diabetes,cardiovascular disease, and mortality.Small interventional studies of T have shown favorable effects on surrogate outcome measures, but a large randomized controlled trial (RCT) with the prespecified outcome of cardiovascular events has not been performed and would be logistically demanding.