Researchers want your body ...

They want to pay me for the use of my body. No, I'm not vain, nor is anyone trying to push me into prostitution. They want me (and you) to be subjects in medical studies.

A poster in my internist's waiting room asks whether I'd be interested in participating in a cholesterol study. In my gynecologist's waiting room, another poster tries to recruit ladies for studies on prenatal vitamins and on vulvar vestibulitis (you don't want to know). On my way home from work, I hear radio ads that go something like this: "Depressed? Come join our study of a new medication."
"The industry has been advertising like crazy," says Diane Simmons, president of the Center for Information and Study on Clinical Research Participation. "It's been a real problem getting people to volunteer for clinical trials, so there's advertising on billboards, on radio, TV and print."
You don't have to be sick to join a study. Often, researchers are looking for healthy people.
There are advantages to joining. You can make money, sometimes hundreds of dollars or more. To a certain extent, you're getting free medical care. If you're sick, you get the chance to try a treatment so new, you can't get it from your doctor. You're also helping your fellow human beings by being a part of medical research.
But before you sign up, here are a few key questions to ask.
1. What are the side effects of the medicine or procedure being studied?
Ask about side effects of the experimental treatment compared with the side effects of your current treatment, advises the National Institutes of Health. What should you expect? Could it make you sick? Could it have long-term effects? Will the doctors in the study follow up with you long-term?

2. Who's making money off me, and will that influence how they treat me?
The doctors running the study might stand to make money if the experimental treatment works, and there are concerns that could influence what they do with you. The nightmare scenario is that they'll enroll you in the study even when the new treatment could harm you or that they'll keep the study going even though the new treatment is clearly causing dangerous side effects.
Alta Charo, a bioethicist at the University of Wisconsin, suggests that you find out whether the recruiters, doctors and nurses involved in the study are "likely to be influenced in their judgments by money or professional connections to the study sponsor."
3. Will it cost me money to be in this study?
Even if they're paying you a stipend, there might be hidden costs. Art Caplan, a bioethicist at the University of Pennsylvania, says to ask very specific questions: If you need to hire a baby sitter while you go to required appointments, who pays? Will the study sponsor pay for lost wages if the treatment makes you sick and you miss work?
For more tips on how to become an Empowered Patient, check out my column at CNN.com/health