Best diet pills?

There must be people out there taking diet pills. I mean, they keep getting made so someone has to be buying them, right? Do people just buy them randomly or do they do research to find the best diet pills? The whole thing is so foreign to me. I've always heard about how terrible diet pills are so I've never honestly considered taking them. I don't understand why someone would take something that has the possibility for terrible side effects and addictions.