I'm not a hard core libertarian to argue about whether banning drugs is good, but even in your scenario customers having information about what is the "medicati

I'm not a hard core libertarian to argue about whether banning drugs is good, but even in your scenario customers having information about what is the "medication" made of and any addictive properties those things might have would go a long way. And lets not pretend that whether a drug is legal (alcohol, tobacco, even marijuana somewhere) or not is result of rational process and not just result of lobbying and historical custom.