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What is a Placebo?

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Updated October 29, 2013

In the beginning, physicians learned that giving sugar pills to patients could have surprisingly good results. For example, if a patient complained of tiredness, weakness or nebulous aches and pains, but the doctor could find no underlying cause, a pill containing no medication would often produce relief from the symptoms. Whether the patient's belief that the pills would help caused the improvement, or the attention of the physician and the act of receiving treatment made the difference, it was plain that prescribing inert medication could in some cases make someone feel better. Thus these sugar pills came to be called placebos - "placebo" being the Latin word for "I shall please."

"It's amazing," one healthcare worker told me, "what you find in studies." People with chronic insomnia, he said, report that they slept wonderfully on their new medications - that turn out to have been inert placebos. They believe the pills will help them sleep - and they do. This is called the "placebo effect."

More recently, drug companies have begun to produce "active placebos." These pills, unlike the sugar or starch pills of old, contain ingredients that mimic the common side effects of the drug under study. An active placebo might, for example, cause dry mouth if the drug being tested was amitriptyline, but it probably wouldn't cause drowsiness because amitriptyline is used to treat sleep disorders. It would be important to know whether people slept better when taking a placebo that medically wouldn't have that effect.

Sometimes a prescription medication is used as an active placebo. In a study published in the New England Journal of Medicine (March 31, 2005), the combination of morphine and gabapentin for relief of neuropathic pain was compared to each drug alone and to an active placebo. The placebo used was lorazepam, a benzodiazepine medication with anti-anxiety and sedative properties, with a common side effect of dizziness. Two of the most common side effects of both morphine and gabapentin are dizziness and sleepiness. "[A]pproximately one-third of the patients," reported Medscape, "guessed that they were receiving an active drug while they were receiving the lorazepam placebo, which could have decreased the difference between treatment with gabapentin or placebo." However, even so, the trial results showed significantly better results for the combination of gabapentin and morphine than either drug alone, and the poorest results for the lorazepam placebo.

The use of placebos, especially active placebos, is not without controversy, but no better way has been found to evaluate the efficiency of trial medications than to to test them in double-blind, placebo controlled studies.

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