What is that concept where you buy a more expensive item as opposed to a generic one b/c you think it's better

it's more like a scientific term; however, they used regularly in the 90's to describe something medically tricky. for example... you have a headache, you buy an aspirin, and it's not working on you. you go to the doctors, the doctors prescribe you $75 pills, and it works for you... only to find out that those $75 pills are just aspirin. but since you paid so much for a pill, your mind tricked your system into believing that those are "miracle" pills and they can help you relieve your headache. what is that called? is it the doppler effect? i forget...