Thursday, July 5, 2007

The Placebo Effect and the Brain

The placebo effect is the tendency for people to respond actively to an inactive medication, to gain a benefit from treatment merely because they expect the treatment to work. In essence, the placebo effect is a state of willed wellness and active anticipation. There is a compelling link between pain and placebo, as it is widely known that “sugar pills” can reduce the perception of pain. One study of placebo for post-operative pain found that placebo was 56% as effective as morphine, even though morphine is considered to be a highly potent analgesic. This simple observation makes it clear that placebo cannot be defined as an “inactive” medication: if dulling pain is the desired result, then pain-killing placebo is active.

Is it possible that placebo is simply the medical name that we give to hope? This concept would explain a great deal about the placebo effect. Any patient who undertakes therapy in a state of hopeful expectancy is apparently primed to show a placebo effect. An expectation of benefit from medical treatment is much like an expectation of reward from any other behavior, and the placebo effect seems to engage the “reward circuitry” of the brain. This circuitry probably evolved to motivate survival-enhancing behaviors like eating or mating. The placebo effect thus appears to be hardwired in the human brain, as it depends upon primordial and quite powerful brain circuitry crucial to our survival.

It would be incorrect to dismiss the placebo effect as being “all in your head,” as if that made it somehow less than real. The placebo effect is not imaginary; the physiological events that are induced by a placebo are often similar to the physiological events that are caused by the drug that the placebo replaces. Placebo given instead of morphine can cause respiratory depression, just like real morphine; placebo given instead of L-dopa can moderate tremor in Parkinsonian patients, just like real L-dopa; placebo given instead of cyclophosphamide can cause suppression of the immune system, just like real chemotherapy; and placebo given instead of analgesia can reduce heart rate in a person experiencing pain, just like a real painkiller.