Depends what it is as said. There was that drug that nearly killed six people recently.
I work in a hospital so I see clinical trials all the time. If your going to do one, try doing something like, measuring the cholesterol levels of men between the ages of 45-60 who are overweight. Or asthmatics who smoke, usually there's nothing being injected with these, just blood samples and lung function tests. They pay time and expenses, so you can make quite a bit with absolutely no real risk to your person.
Contact your local hospital to find out if they run any trials and what they are.