Here’s a potentially mischievous idea for solving the problem Mike posed — using fingerprinting technology when you sell the drug, say, for example, an RFID tag in each pill’s section of a blister pack that will render it null if opened by someone other than the buyer.
Loads of problems with this idea — what about nurses and caretakers giving medicine to people? What about the ability to manipulate the technology tag? And so on.
But the essential point is that to sustain the kind of price discrimination that creates the producer surplus that funds investment and research in such industries, the ability to prevent resale is crucial.