A placebo is a pill or other substance that has no therapeutic effect. Many people think that clinical trials involve placebos, but only a small fraction of cancer clinical trials use them. If a placebo is part of the trial you’re considering, you will be fully informed of that fact ahead of time. You would only be considered for such a trial when it’s safe and medically appropriate. A placebo in cancer treatment is most commonly used when a standard treatment is available to patients and we want to compare that standard treatment to a new treatment.