There is no job that tests for steroids. "steroids" includes almost 4 dozen drugs, most of which have their own tests for detection. Thats beyond absurd and would require a very expensive series of blood tests.
So,.. you can safely add "liar" to "impotent".
Why is this even puzzling? It could be a physiological problem, it could be that he's not turned on by her, it could be drugs/drug addiction, alcohol abuse, steroids or any number of psychological reasons. I could imagine a lot of reasons for this.
Why are you asking a bunch of unqualified dipshits to diagnose someone with no facts as if you're asking about simple and one dimensional such as what to do when a lightbulb stops working?