Paul-Labrador et al1 conducted a randomized controlled trial of transcendental meditation (TM) vs health education to determine the benefits of meditation on components of the metabolic syndrome in patients with coronary heart disease (CHD). The authors correctly identified a number of limitations of their study. However, I wish to point out an important limitation that they did not discuss. In a study of this nature, patients with an interest or belief in meditation are more likely to consent to participate; thus, the sample is likely to be biased toward meditation from the outset. This, coupled with the impossibility of patient blinding to treatment allocation, is likely to magnify the placebo response in the meditation group and correspondingly diminish the treatment response in the control group.
Andrade C. Transcendental Meditation and Components of the Metabolic Syndrome: Methodological Issues. Arch Intern Med. 2006;166(22):2553. doi:10.1001/archinte.166.22.2553-a