[edit ] Placebo-controlled studies

Prescription placebos used in research and practice

Beecher (1955) reported that about a quarter of patients who were administered a placebo. for example against back pain, reported a relief or diminution of pain. Remarkably, not only did the patients report improvement, but the improvements themselves were often objectively measurable, and the same improvements were typically not observed in patients who did not receive the placebo.

Because of this effect, government regulatory agencies approve new drugs only after tests establish not only that patients respond to them, but also that their effect is greater than that of a placebo (by way of affecting more patients, by affecting responders more strongly or both). Such a test or clinical trial is called a placebo-controlled study. Because a doctor's belief in the value of a treatment can affect his or her behaviour, and thus what his or her patient believes, such trials are usually conducted in "double-blind " fashion: that is, not only are the patients made unaware when they are receiving a placebo, the doctors are made unaware too. Recently, it has even been shown that "mock" surgery can have similar effects, and so some surgical techniques must be studied with placebo controls (rarely double blind, due to the difficulty involved). To merit approval, the group receiving the experimental treatment must experience a greater benefit than the placebo group.

Nearly all studies conducted this way show some benefit in the placebo group. For example, Khan published a meta-analysis of studies of investigational antidepressants and found a 30% reduction in suicide and attempted suicide in the placebo groups and a 40% reduction in the treated groups. (Khan 2000) However, studies generally do not include an untreated group, so determining the actual size of the placebo effect, compared to totally untreated patients, is difficult.

[edit ] Notable placebo effect absences

In psychological treatment, two disorders are known to have very low placebo effects: schizophrenia. and obsessive compulsive disorder. [citation needed ]

[edit ] Placebo and pain

Careful studies have shown that the placebo effect can alleviate pain, although the effect is more pronounced with pre-existing pain than with experimentally induced pain. People can be conditioned to expect analgesia in certain situations. When those conditions are provided to the patient, the brain responds by generating a pattern of neural activity that produces objectively quantifiable analgesia. (Benedetti 2003, Wager 2004)

Evans argued that the placebo effect works through a suppression of the acute phase response. and as a result does not work in medical conditions that do not feature this. (Evans 2005) The acute phase response consists of inflammation and sickness behaviour:

Four classic signs of ‘inflammation’: tumor, rubor, calor and dolor – swelling, redness, heat and pain. Sickness behaviour: lethargy, apathy, loss of appetite and increased sensitivity to pain.

[edit ] Placebo and depression

A brain-imaging study found that depressed patients who responded to the placebo effect showed changes in cerebral blood flow, which were similar to the changes in brain function seen in patients who responded to anti-depressant medication. (Leuchter 2002) Other studies argue that up to 75% of the effectiveness of anti-depressant medication is due to the placebo-effect rather than the treatment itself. (Khan 2000)

[edit ] Endogenous Opiates

Endogenous opiates are chemicals produced by the brain that suppress pain and produce analgesia and a sense of well-being. Opium and drugs derived from it (opiates ) produce their "highs" by triggering the same brain receptors used by natural opiates. Increased release of endogenous opiates like endorphin is associated with pleasant experiences like exercise (the runner's high) and sex. When patients who claimed to experience pain relief after receiving a placebo were injected with naloxone (a drug that blocks the effects of opiates), their pain returned, suggesting that the placebo effect may be partly due to the release of natural opiates. (Sauro 2005)