What should i do about this? Plz Help!!?

my guy friend who runs track with me has started taking steroids. he says they're "just muscle supplements" but yeah uhm steroids. they've been making him sick where he has to actually leave school. hes already one of the best guys on the track team and has a lot of muscle but he self concious about his body like at the one track meet he had me and my other friend stand in front of him so he coul take his shirt off ad remove his undershirt. also in track we have like shorts that are kinda short when we run and thy shift up when we run too and that makes him uncomfortable and i understand that. i really don't want to tell the coaches cuz then he won't be able to be on the team or play football anymore. but he won't listen to me or my friend when we try to talk to him about it. he gets all sensitive about it.