What is the placebo effect?

A placebo is a dummy treatment — such as a sugar pill or saline injection — that has no active medicinal ingredient, yet patients often report genuine relief after taking one. This placebo effect arises from psychological and neurological factors: expectation of benefit can trigger the brain to release natural painkillers like endorphins and dopamine, and the ritual of being treated reduces anxiety. The effect is strongest for symptoms shaped by perception, such as pain, nausea, and fatigue, and weakest for measurable disease processes like tumour growth. Because of it, rigorous clinical trials use double-blind, placebo-controlled designs in which neither patients nor researchers know who receives the real drug, so any true benefit of a medicine must exceed the placebo response to count. A related phenomenon, the nocebo effect, occurs when negative expectations cause harmful symptoms.