One must be very careful if choosing to take part. Of course no company wants the trials to go wrong and probably takes every possible precaution before testing in humans & how trials are carried out (e.g. dosage), the uncertainties lie in the vast complexity of living cells and organisms. Indeed, drugs are tested on animals first in most cases, but the biochemistry of animals and the effect of a drug on one species may not reflect that of such on another. One cannot predict or even know of what happens when a drug is given to a human, hence the initial trials. Read what happened to the participants in the Northwick Park trail last year, I distinctly remember one man on television, his fingers black and crumbled away, unable to walk, go to work or do much at all. I'd imagine the risk lessens at later phases, but the higher paying trials seem to be the earlier phases (yes, I did consider this for myself). Personally, I wouldn't feel happy taking part unless I understood the science behind it and even then there would be (great) risks involved. Whilst a bit a cash for a few days sounds like easy money, the risk to my health is too high a price to pay. You can't buy back your health. I'd rather be the couple of grand poorer whilst a student.