I did various medial trials in college for money and have mixed feelings about this. When sitting in the various waiting rooms, it was very clear that was only one kind of person that did "open" (not targeting people with a disorder but rather recruiting healthy volunteers) medical trials: the poor. I got to know lots of of people well (we were frequent flyers in the medical trial world), and our common characteristic was that we really needed the money.

It's kind of like non-pay electoral offices. You only get candidates that can afford not to work. In medical trials, you get the kind of people that are willing to, for example, get infected with the common cold and have you blood drawn 6x a day for 4 days for about 80 bucks a day. It was not horrible, but often uncomfortable. Study recruiters still call me, and now that I have a decent paying job there is no way I would ever consider doing those kinds of studies again. Simply not worth it.