By definition, a clinical trial is trying something new that hasn't been fully tested, so, yes, there are risks due to possible side effects, drug interactions, or other symptoms that the researchers don't yet know about. Of course, researchers want the drug or method to be safe and to protect patients from harm, so you can be sure they have patients' interests at heart. And if it's a phase III trial, which is most common, the treatment has already been tested in previous trials. Still, entering a clinical trial does pose additional risks that you should be sure to understand fully.