Drug Uses

In recent years, there is renewed interest in understanding the medical uses of certain drugs, some of which are Schedule I Substances. Specifically, marijuana, Psilocybin, and MDMA may all have potential medical uses.
Other than the obvious legal side, what do you believe are the major ethical/moral barriers to utilizing such drugs? If MDMA can help the many veterans suffering from PTSD, is it not worthwhile exploring its use to help people in need and for whom traditional psychiatric drugs have not worked?

Answer in favor of usage for people with PTSD