Supposedly you can be hypnotised so that at your will you can feel no pain. The example often given is going to the dentist for a filling, and not require a local anaesthetic and not feel pain. This is acheived (apparently) by just isolating the area where you don't want to feel pain in your mind, and turning on the no pain trigger, which might be touching the tip of your thumb with the tip of your index finger or whatever the hypnotist has programmed you with.
Hypnotism has been used in surgery a fair bit instead of using anaesthesia but the person is actively being hypnotised before and during the surgery. This post-hypnotic suggestion trigger which allows you not to feel pain whenever you need is the sort of thing that would be perfect if hypnotism really could activate the effects of a drug by just initiating the physical trigger mechanism for your desired drug.
I just would have thought if it was possible we would have heard more about it by now and there'd be a whole tonne of youtube videos about it.