Placebos are often used in clinical drug trials to determine how well a potential medicine will work.
There are two different groups of subjects in a placebo-controlled trial - one receives the experimental drug and the other the placebo. Neither researchers nor subjects know which group is receiving the real drug or the placebo.
Some researchers are questioning the placebo-controlled trial. Not everyone thinks a drug is ineffective if the placebo performs better.
Other critics of the placebo-controlled trial state it's wrong to attribute all positive outcomes to the placebo because many illnesses can resolve without any treatment.
When a patient takes a placebo and experiences adverse side effects, it's called a nocebo effect. Patients taking active drugs have also been known to have side effects that can't be directly attributed to the drug.