Taking testosterone increases muscle strength and helps immune system function.

The finding

What the evidence shows

Restoring testosterone in men whose levels are low does have measured benefits, including more lean muscle mass, better sexual function and modest mood improvement in the NIH-funded Testosterone Trials. The immune part is the weak link. Reviews of the research describe androgens including testosterone as generally immunosuppressive, cutting antibody production, T cell proliferation and natural killer cell activity, which is one reason men are more prone to some infections than women. There is no established finding that testosterone therapy makes the immune system work better.