A placebo is a pill or substance containing little or no medication and is prescribed to reinforce a patient's expectation of getting well; also used as a control in clinical research trials to determine the effectiveness of a potential new drug or treatment. Generally, a Patient who thinks they are on the correct treatment will gradually get well through their own belief of the drug, hence for clinical testing purposes, they must eliminate any such recovered "symptoms" by administering two groups, one which receives the actual drugs and ones who receive a placebo. Thus, while both groups will exhibit some form of recovery, the group with the actual drug will yield the results of the actual drug, unhampered by their own feelings. This is also a way to tell what kinds of side effects might take place. However, if one started on the placebo, and is subsequently given the real drug (even if only once) then their results are nullified, as it will be impossible to tell what recovery/symptoms he/she suffers is by the drug or their own will. There is often a large group of people in either test groups, so that only uniformed effects are in the results.