The dose makes a poison. And there is a very big difference. For one the stuff you get at the pharmacy is pure and is reasonably dosed. No residue of other substances that might have more adverse effects.
Secondly, heroine and cocaine were used in medicine not very long ago and they're very effective. The reason why they're now blacklisted is because people were/are abusing them. Plus there are safer substances nowadays that are still dangerous but obviously there's a risk/reward situation here. By the way, marijuana is on the very same list in a lot of countries(not in Canada as far as I know).
The problem is knowledge and that's what your pharmacist is supposed to be there for. Sadly in most countries the pharmacist has become just another salesman. That's why I hear "I don't want chemistry, I want something natural." every day. When I tell them that morphine and cocaine is just as natural as tobacco, chocolate, caffeine and alcohol they usually won't believe me.
Poison is poison no matter what the quantity is. Saying that only taking small quantities of cocaine, heroin or meth is okay is nothing but a myth because guess what, you still put poison in your body which in reality does'nt actually cure anything. People only think they feel better because they are stimulated by a drug and are ******* high. Once the substance runs it's course it's back to square one and they'll need another dose to feel "better" again.
Pharma wouldn't be in business if they actually cured anything, they want you coming back just like the thug selling drugs on the street.