The use of any medical treatment potentially involves small risks, whether or not you are on a clinical trial. However, in a clinical trial, there is usually less known about the risks of the experimental treatment arm than there is about the standard arm or arms. You will be made aware of whatever knowledge is available about the risks of the new treatment, and will be informed that it is possible new information on side effects or risks will emerge during the clinical trial. If there is new information discovered during a trial that would potentially affect whether patients would consent to treatment, that information is shared with the investigators and patients. Sometimes, if the information is quite significant, the informed consent document will be revised to include the new information, and patients who have already consented will be asked to indicate whether they continue to consent to their treatment in the study.
As described above, a clinical trial often includes more tests and visits than would be standard, so that risks and side effects can be identified as clearly as possible. There are often small risks associated with medical tests. All of the anticipated risks of the study treatment and tests will be described in the informed consent document, to help you make your decision about the trial.