Placebos have been misunderstood as resulting from the “power of positive thinking.” This misconception fails to take into account the complex neurobiology that occurs in any treatment regimen.
DEFINITION OF THE PLACEBO EFFECT
Ø The placebo effect is a phenomenon in which a person’s expectations determine a particular outcome.
o Drinking decaffeinated coffee (placebo) thinking it is regular coffee (active agent) may give a stimulating effect similar to regular caffeine.
DEMONSTRATIONS OF THE PLACEBO EFFECT
Ø Post-operative patients given an open-view saline injection (placebo with the expectation of analgesia) compared with patients who received a machine-infused intravenous administration of 8 mg morphine (active drug with no knowledge of when the drug would be infused) experienced the same level of pain relief.
Ø After participating for a month in a placebo controlled antidepressant trial evaluating the effects of a new antidepressant, a patient overdosed on 29 of the drug-study pills. His blood pressure dropped to 80/40; he began to hyperventilate, became tremulous, and was given intravenous stabilization for four hours. Within fifteen minutes of being notified that he had been taking a placebo, the patient’s blood pressure rebounded to 126/80 and he felt fine.
Ø A meta-analysis study that examined clinical trials for antidepressant medication versus placebo showed an increase in placebo effect over the last two decades that mirrored the increased response to active drugs.
o For example: When Prozac was initially studied, approximately 40% of subjects responded to the antidepressant effects of Prozac while depression lifted in 20% of patients receiving placebo. Currently, about 60% of depressed patients respond to Prozac while 30% of depressed patients receiving placebo respond with an improved mood.
Ø When the brains of patients with Parkinson’s disease were analyzed by positive emission tomography following placebo saline injection increases in dopamine levels in the caudate nuclease and the putamen were comparable to those seen after an injection of levodopa.
PLACEBO EFFECT IS MORE THAN POSITIVIE THINKING
Ø Naloxone (an opioid receptor antagonist) blocked the expected analgesic effects of saline injections when subjects thought the saline injection that there were given was morphine.
o This important study shows that because naloxone blocks the effects of the saline induced opioid release, a chemically inert agent (saline) can trigger the release of endogenous opioids.
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