When we take a drug our bodies react to it. The body has now learned a new way of creating a certain state. Through hypnosis or any other method that works.. the drug state can be recreated. This is usually done by getting the person to remember a time they took the drug. I seen Derren Brown make a guy drunk. His friends said it was exactly the same as when he was inebriated. And the bonus is... no hangover! It's all about belief. I you believe you can do something.. you can. The placebo effect.

I'll try to dig out more info on this subject.