Ever heard about "nocebo effect"?

"We have long known that expectations of a malady can be as dangerous as a virus. In the same way that voodoo shamans could harm their victims through the power of suggestion, priming someone to think they are ill can often produce the actual symptoms of a disease. Vomiting, dizziness, headaches, and even death, could be triggered through belief alone. It’s called the “nocebo effect”.

But it is now becoming clear just how easily those dangerous beliefs can spread through gossip and hearsay – with potent effect"}
http://www.bbc.com/future/story/20150210-can-you-think-yourself-to-death

Yeah, I've heard of that before.

So, a Shaman really does this : Power up the psychological effect of drugs as well, by being confident.
Apart from other effects.
Psychology seems to have a far bigger role in us than we want it to.

There is no need for drugs anywhere.
Possible effects of selfsuggestion and selfmesmerism are known for centuries.