Is there a general word for someone or something popular or loved by the masses but that has not been proven to be effectual (like how some would use the term "pop psychology" pejoratively)? Examples would be how things like popular psychology or holistic medicine are accepted excitedly by numerous people while not being proven to be useful to the majority.
UPDATE: Thanks for you responses. I think the word "fad" (or "hype") would come closest to what I was looking for (thank you for that).
But is there a more general or appropriate term? I'm not American so apologies in advance (this is strictly for the sake of discussion): the only example I can think of is certain voters who were initially excited about Obama, but came to be disappointed after he failed to meet their expectations. Is there a word that could be used to describe Obama in this context? Something well-loved which turns out to be a disappointment.