Wednesday, May 20th, 2009
What we really mean by “the placebo effect” is not some mysterious effect from giving an inert treatment, but the complex web of psychosocial effects surrounding medical treatment. Those effects occur with effective treatments too, not just with inert treatments.
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We not only know placebos “work,” we know there is a hierarchy of effectiveness:
"How Could It Work?
- Placebo surgery works better than placebo injections
- Placebo injections work better than placebo pills
- Sham acupuncture treatment works better than a placebo pill
- Capsules work better than tablets
- Big pills work better than small
- The more doses a day, the better
- The more expensive, the better
- The color of the pill makes a difference
- Telling the patient, “This will relieve your pain” works better than saying “This might help.”
If the placebo effect is real, what might the mechanism be? We can’t just write it off as delusions of hyper-suggestible patients. There’s evidence that several things might be going on.
The main hypotheses are: expectancy, motivation, conditioning, and endogenous opiates.
- Expectancy is an established psychological phenomenon. It even affects vision: we are more likely to see what we expect to see. Wine tastes better if the price is higher. Kids like fast food better if it comes in a McDonald’s wrapper. If we expect to feel pain we are more likely to feel pain. If we are told to expect a strong painkiller, we’re more likely to get pain relief.
- Motivation, the need or desire to improve health or get relief, has been shown to contribute independently to the placebo response. Patients who are strongly motivated to get well are more compliant and follow health advice more conscientiously. And patients who are more compliant about taking their placebo pills regularly get a stronger placebo response.
- Conditioning is what Pavlov did to his dogs. People learn to associate pills and medical treatments with relief of symptoms. The body even learns physiologic responses: dogs salivate when injected with morphine; after they become conditioned, injecting a placebo makes them salivate, although not as much.
- Endogenous opiates are pain-relieving chemicals produced in the brain that mimic the effects of opium-like drugs (morphine, etc.). There is some evidence that when patients respond to placebos, their brains produce more of these chemicals. Imaging studies have shown activation of opioid receptors in the brain when people are told that a placebo is a painkiller. And there is evidence that giving a drug that blocks the effect of narcotics can also block the placebo effect.
Friday, June 26, 2009
The Placebo Effect by Harriet Hall, MD
The point is that high school education is a complex web of psychosocial effects. Understanding why placebo works should help to clarify how education works.