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.
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- 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.
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- Phases of drug trials: from animals to Phase IV — Every phase of testing has to account for expectancy.
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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.
Términos del curso
Las palabras de tu profesor, tal cual aparecen en las diapositivas. Aprende el término y esta definición; la explicación de abajo solo ayuda a entenderla.
- Expectancy effects
“The expectations that people have about a treatment influence the effects of that treatment”Diapositivas 07, p. 4
The reason RCTs need a control group.
- Placebo effect
“Placebo effect – positive outcome from receiving a “sham” or “fake” treatment”Diapositivas 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”Diapositivas 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”Diapositivas 07, p. 4
Doesn't have to be a drug, or even something ingested.
De tu curso: Course slides 07, pp. 4–16 · Midterm study guide: Clinical Trials and Policy
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