The placebo effect refers to a measurable, genuine improvement in a patient's symptoms following treatment with an inactive substance or sham procedure, one with no inherent therapeutic value. For decades, researchers assumed the placebo effect was essentially a psychological illusion, a matter of patients simply believing they felt better without any actual physiological change occurring. However, more recent research using brain imaging has revealed that placebos can trigger real, measurable biological responses, including the release of the body's own natural pain-relieving chemicals. The strength of the placebo effect appears to depend on several factors, including the patient's expectations, the perceived authority of the person administering treatment, and even the physical characteristics of the placebo itself; larger pills, for instance, tend to produce a stronger placebo response than smaller ones, and injections often outperform pills entirely. This has significant implications for clinical drug trials, in which new medications must be shown to outperform a placebo before they can be approved for widespread use. Interestingly, some studies have found that placebo effects can occur even when patients are explicitly told they are receiving an inactive treatment, suggesting that the ritual of treatment itself, rather than deception, may partly drive the response.