Category A - approved by the FDA, basically what we have right now
Category B - approved by some other established regulatory body (EU). Comes with all the warnings, doctors can write it off-label, insurance companies may not cover it but doctors can ask for a variance
Category C - approved by some non-OECD body. Insurance companies under no obligation to cover
Category D - experimental, this is stuff maybe still only in animal models, but pharmacies can still order and dispense it
Category E - experimental and basically limited run from pharmaceutical companies. These essentially need to be tailor-made or produced by a GMP kilo lab. There are plenty of drugs in this category - I worked on them - and the intended recipients are entirely animals, QA, and regulatory agencies. But maybe if some crazy S.R. Hadden type (billionaire in Contact) wants to guinea pig themselves, let em.
The latter category also opens the door for custom therapies (gene/mRNA) that you basically can't test the active pharmaceutical ingredient for efficacy on.