Are you a pharmacist? If not you should really talk to a legal advisor, dealing in pharmaceuticals is sadly heavily regulated by most governments so you might be open to litigation.
How would they stop customers from sending him funds?
They would not, but they can sure as hell clamp down on some dude aquiring and sending out prescription medication in large quantities to unknown recipients, much easier so if he is not a pharmacist/doctor.
Big pharma has a way of distributing cheap drugs to third world countries who have large black markets for selling these goods locally. Bitcoin + anonymous networks like Tor would allow these local markets to go international (not that I would condone or approve of such a thing.)