To follow up on my last message I'll address a few points:
1) Yes, Thalidomide led to horrific outcomes. The problem was that modern day clinical trials were not around yet, not the animal testing. The Thalidomide tragedy (and others) have led to the
modern practice for clinical trials which is so extensive that it might blow your mind. Check the link and pay special attention to the number of people involved for each phase, the time and money invested and the relative success rate for target compounds.
2) Why don't we use prisoners for clinical trials? Well, I'm not going to get into the obvious ethical problems but there are many sheer logistical problems with this idea. What if you're investigating a small molecule with the hopes of treating pancreatic cancer? It wouldn't really do any good to use this compound with perfectly healthy people (aside from answering other questions such as pharmacokinetics or toxicity) so we need people suffering from pancreatic cancer. How many of the 130,000 imprisoned people in america have pancreatic cancer? Not many. That is just one disease, and there are so many diseases that require different therapies. You would not have enough people to do all the testing that is required to ensure safety for the rest of the population.
Fortunately, we don't live in a country with a tyrannical leader that would enforce such forced therapies.