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.
Recorrido
Placebo, active placebo, nocebo
Placebo: a positive outcome from a sham treatment (a sugar pill). Active placebo: gives side effects such as dry mouth but no psychoactive effects. Nocebo: the same thing with negative effects — and it doesn't have to be a drug, or even something swallowed.
Analogía y ejemplo resuelto
Analogía: Expectancy is like a stage light. The same actor (the drug or sugar pill) looks different depending on the lighting — price tags, white coats and injections turn the light up; warnings about side effects shine a spotlight on every twinge.
Participants given an identical sugar pill report more pain relief when told it costs $2.50 than when told it costs 10 cents. Explain.
- The pill is identical, so the difference isn't pharmacological.
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