A placebo effect is a phenomenon of medication or medical treatment, even inert or ineffective ones, to exhibit results simply because the recipient believes that it will work.

Placebo effect may also refer to:

• Placebo Effect (band), a German dark electro band
• Placebo Effect (film), a 1998 American thriller film
• "Placebo Effect" (song), a 2023 song by D4vd
• Placebo Effect (novel), a 1998 novel by Gary Russell
• "The Placebo Effect", an episode of the television series The Twilight Zone
• "Placebo Effect", a song by Siouxsie and the Banshees from the 1979 album Join Hands

• Placebo (disambiguation)
• Nocebo effect, the phenomenon of a patient's expectations for a treatment causing the treatment to have a worse effect than it otherwise would have