What are “blinded” clinical trials?

A clinical trial is “blinded” when participants do not know which group they have been assigned to. In other words, they are not aware of whether they are part of the study group receiving the new intervention being tested, or whether they are in the control group receiving a standard-of-care intervention or an inactive placebo. Some clinical trials go one step further to be "double-blind." In this case, neither the participants nor the researchers know who is receiving the intervention and who is in the control group. Clinical trials are often done in a blinded way so that neither the participants' nor the researchers' expectations about the intervention can influence the results.