No one is going to dump a few hundred million into developing a new drug if everyone can manufacture and sell it upon release.

You won't sell it on the market because you have to produce it cheaper or at the same cost as the competition. You don't have the knowledge to produce the drug efficiently, and you can't learn that by looking at the end product. In a society without IP, the most important things are the optimised production processes, which will be kept secret. The rest can be copied because it will be more expensive to produce.