I'd imagine a lot of the 'normal' prescriptions are ok too. Not steroids or stuff like that, but without reading the rulebook and the anti-doping policy (which is of course on the ATP site if you really want to know for sure), I'd guess most of the stuff is ok.
As far as I'm concerned, this is all bogus and total
When one of the well-known tennis writers write about it (even if it's a less reputable ne), then we'll talk. He still serves well over 140mph and he still hits a huge forehand once in a while (see: Verdasco match a few days ago), so to suggest he's lost power in his arm or something is just... well.... nonsensical to me