Why does legality play a role at all?
Philosophy aside, tylenol will seriously fuck up your day and is entirely legal, while I think we are all aware of certain "illegal" drugs that are completely harmless. It is pretty obvious that these laws are not looking out for our health. Hell, the FDA requires that drug companies load up some legal drugs with tylenol simply to make it deadly. Regardless of my opinion on the rule of law in general, something so blatantly anti-health should be disregarded on the spot.
Modern drug laws are the moral equivalent of laws mandating self-flagellation.