In response to my last post, which proposed that Transcendental Meditation and other cults might be exploiting the placebo effect, some readers cited studies supposedly showing that TM has therapeutic benefits. Well, sure. There are lots of studies showing that lots of forms of meditation can yield lots of benefits. But the research is unimpressive, to say the least, and is corrupted by the "allegiance effect," the tendency of proponents of a treatment to find evidence that it works. (The term was coined by a Lester Luborsky, a prominent psychotherapy researcher.)

For a critical overview of meditation research, see a 2000 article in the Journal of Consciousness Studies, "Meditation Meets Behavioral Medicine," which I discussed in my 2003 book Rational Mysticism. Author Jensine Andresen, now a religious scholar at Columbia, reviewed more than 500 papers and books on meditation published over the last half century. Andresen cautioned that there are thousands of techniques that could be categorized as meditation; it is virtually impossible to define the term in a way that does justice to this vast diversity.

Not surprisingly, she said, attempts to measure meditation's neurological effects with brain-wave monitors, positron emission tomography, and other techniques have yielded widely divergent findings. Meditation has been "prodded and poked by a variety of technological apparati, with inconclusive results," Andresen commented. For every report of increased activity in the frontal cortex or decreased activity in the amygdala, there is a conflicting finding.

Investigations of meditation's therapeutic benefits have been equally inconclusive. Meditation has been linked to a dizzying array of benefits, including the alleviation of stress, anxiety, high blood pressure, substance abuse, hostility, pain, depression, asthma, premenstrual syndrome, infertility, insomnia, substance abuse and the side effects of chemotherapy. But many of these studies have been poorly designed, Andresen remarked, carried out with inadequate controls or no controls at all.

Andresen noted that meditation has been linked to adverse side effects, too, including suggestibility, neuroticism, depression, suicidal impulses, insomnia, nightmares, anxiety, psychosis and dysphoria. In an implicit reference to the cultish context within which meditation is often taught, Andresen added that meditators may become vulnerable to "manipulation and control by others," including "unscrupulous or delusional teachers."

A similar picture emerges from the 2007 peer-reviewed report "Meditation practices for health: state of the research," by the National Center for Complementary and Alternative Medicine. The report analyzed 813 studies of meditation and concluded that most were of "poor quality."

The report stated: "Many uncertainties surround the practice of meditation. Scientific research on meditation practices does not appear to have a common theoretical perspective and is characterized by poor methodological quality. Firm conclusions on the effects of meditation practices in healthcare cannot be drawn based on the available evidence." If your particular form of meditation makes you feel good, do it! But don't kid yourself that its medical benefits have been scientifically proven.

Image: http://www.ophpen.org.