According to Dylan Evans (Placebo. The Belief Effect. 2003), there are no well controlled clinical trials which demonstrate that patients with anxiety and depression do better when given a placebo compared with no treatment. However, there are other kinds of evidence while do provide a basis for suspecting that placebos can reduce anxiety and depression. Results from a study* of patients with anxiety and phobias who were all given the same dose of an anxiolytic drug but in tablets of different colours showed that there were significant differences in the responses of patients according to the colour of the tablets (green were the most effective in reducing anxiety while red ones were the least effective). A large meta analysis of studies of antidepressants also suggests a placebo effect in depression.** When patients were able to guess which group they were in (active treatment or placebo), the differences between the active treatment group and the placebo group increased which suggests that belief is playing some role in the efficacy of the antidepressant medication. In other words, the placebo effect does seem to work for depression.
*Schapira, K., H.A. McClelland et al. (1970). Study on the effects of tablet colour in the treatment of anxiety states. British Medical Journal 2:446-449
**Kirsch, I. and G. Sapristein (1998). Listening to Prozac but hearing placebo: a meta-analysis of antidepressant medication. Prevention and Treatment 1, Article 0002a. http://journals.apa.org/prevention/volume 1/pre0010002a.html
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