Although placebo agents are often chosen in blinded clinical trials because they do not have clinical effects, patients may be able to differentiate placebo from active drug and thereby unblind the study. To make this awareness difficult, active placebos may be used. An active placebo is a drug that has no effect on the condition being treated but does simulate medical therapy, often through other side effects. For instance, consider a trial investigating chemotherapeutic agents, which often have known side effects of nausea and vomiting. An active agent would have no specific therapeutic effect on the patient's cancer, but would provoke nausea and vomiting.
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