A placebo is an inactive substance that has no treatment value. Placebos can come in a variety of forms, including pills, liquid, powder, or other interventions. They are used in studies to provide a comparison for the intervention being studied.

Use of placebos may lead to improvement or worsening of health status because of a patient’s beliefs. Due to this, use of placebos is most ideal in randomized-controlled trials.

Source: Požgain, I., Požgain, Z., & Degmečić, D. (2014). Placebo and nocebo effect: a mini-review. Psychiatria Danubina, 26(2), 100–107.