Today we all here about the evils of drugs and the various attempts to stop drug trade since the Opium wars. However, I been wondering if there were any drugs being traded around against the law in the middle ages. Were there any medieval Walter Whites running around?
Can't comment on the existence of specific substances being outlawed in pre-modern times, but keep in mind that the concept of legality is very different in the absence of the authority to back it up.
Without a widespread respect for laws, monopoly on violence, impartial court system, etc. there isn't really any way of regulating (ab)use of certain substances. There might be religious and social norms (like the islamic ban on alcohol), but that's not the same as civil legislation and would be enforced quite differently.