what’s the science behind the placebo effect?
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Oh hey, I did my thesis on this topic!
The ELI5 is that placebos don’t work for everything but can be quite powerful for particular conditions or people. They usually work because of expectations (I believe I will feel better) or learned association (I take a placebo with an active medication repeatedly, and then later the placebo alone can make me feel better). This is also similar for the ‘nocebo’ effect where I might feel worse or get bad side effects to taking something for the same reasons.
A bit more beyond the ELI5:
Placebos can have different effects: subjective changes in perception of symptoms (e.g. nothing measurably changes but I feel better anyway), or objectively measurable physical effects.
As mentioned above there are two main hypothesised mechanisms of action: expectation and conditioning.
Expectation is what it sounds like: when we believe that we have been given an effective treatment, we may feel better or even have physiological changes. The evidence is good for subjective effects from verbal suggestion alone, but a bit spotty and inconsistent for objectively measurable effects.
Conditioning (classical conditioning in this case) is learning by association: e.g. the taste of coffee becomes associated with the caffeine hit through repeated exposure, so even decaf coffee or the first smell/taste before the caffeine is actually active can still sometimes make us feel more alert.
A striking example of a conditioned placebo response is from a few studies looking at conditioned immunosuppression. Basically people were given a weird drink and some active immunosuppressant drugs together for a while, then waited a few days so the active drug was out of the system. Then when given the weird drink without the drug, their blood samples showed immunosuppression as if they had taken the drug.*
*Goebel et al. (2002). Behavioral conditioning of immunosuppression is possible in humans.
Wirth et al. (2011). Repeated recall of learned immunosuppression: Evidence from rats and men.
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