TL;DR - men with flagging testosterone levels may be better skipping the supplements.
This article looks at the effects of testosterone on the body, and the effects of testosterone supplements.
Socially testosterone is seen as the MAN hormone. Its effects encapsulate the
"male" attributes - strength, virility, aggression but actually, a lot of men are supplementing their bodies with the hormone when actually, it might not be at all necessary to do so.