It sounds crazy, but I've done it.
Near Fargo, ND, is a place called Cetero Research. They test medications on people.
I didn't grow any extra arms or have my hair suddenly turn green--nor did I see it on others--so the tests are relatively safe.
Check it out in your area. I've made anywhere from a few hundred dollars to a few thousand.
The only drawback was that they didn't take any taxes out, so you had to be extra careful and figure out the tax right. It was almost like one was self-employed. Save at least 25% of what you take in, which is a rule of thumb experts say, so that way you'll have enough to pay Uncle Sam.