Expectancy: placebo and nocebo effects
Explains how expectations alone produce real improvements (placebo) or real side effects (nocebo), what makes expectancy stronger, and the brain mechanisms behind it.
Where this fitsConnects to 3 · Unlocks 1
- Connects to
- Randomized controlled trials: randomize, control, blind — Expectancy is the reason trials need placebo controls and blinding.
- Other messengers: histamine, opioids, hormones and more — Placebo pain relief uses the endogenous opioids you met earlier.
- Why drugs keep reinforcing: prediction, tonic vs phasic, and speed — Conditioning — the same learning that makes drug cues powerful — is one mechanism.
- Unlocks
- Phases of drug trials: from animals to Phase IV — Every phase of testing has to account for expectancy.
Orient
Expectancy effects: “the expectations that people have about a treatment influence the effects of that treatment.” Placebo effect – positive outcome from receiving a “sham” or “fake” treatment. Nocebo – same as placebo effect, but now negative effects. These are all in your head — but that doesn't make them any less real.
Course terms
Your professor's wording, word for word from the slides. Learn the term and this definition — the explanation underneath is only there to help it make sense.
- Expectancy effects
“The expectations that people have about a treatment influence the effects of that treatment”Slides 07, p. 4
The reason RCTs need a control group.
- Placebo effect
“Placebo effect – positive outcome from receiving a “sham” or “fake” treatment”Slides 07, p. 4
In drug studies, a pill made of sugar or something inactive.
- Active placebo
“Active placebo – pill gives side effects (e.g., dry mouth) but no psychoactive effects”Slides 07, p. 4
Side effects make people believe they got the real drug.
- Nocebo
“Nocebo – same as placebo effect, but now negative effects, not positive”Slides 07, p. 4
Doesn't have to be a drug, or even something ingested.
From your course: Course slides 07, pp. 4–16 · Midterm study guide: Clinical Trials and Policy
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