A placebo effect happens when a person reports a positive health outcome from a drug or treatment that is not expected to have any effect. The drug may contain an inactive substance, or the treatment may not have been proved effective. But the person believes they will benefit from the drug or treatment, so they report a positive outcome.

Sometimes a drug or treatment seems to help some people even though studies have shown it is not any better than a sugar pill (placebo). Active drugs and treatments can also have a placebo effect. It is sometimes difficult to know if a certain drug is helpful because of its active substance or because of the placebo effect felt by a person expecting it to be helpful.

The placebo effect suggests that there is a strong connection in how the mind and body work.