The surprising effectiveness of placebos

This came to mind after reading this extract from The Secret of Our Success by Joseph Henrich:

Depending on a person’s beliefs, desires, and prior experiences, taking a placebo or experiencing any “sham” medical procedure including fake surgery can activate biological pathways in the body. Often these pathways are the very same pathways triggered by the active chemicals in popular drugs. Placebos can reduce pain, activate the immune system, mitigate irritable bowel symptoms, improve motor coordination in Parkinson’s patients, and ameliorate asthma. The more you believe it will work, the more it may actually work. Not only that, there appears to be a synergistic interaction between the size of the placebo effects and the size of the chemical effects; that is, the more one believes a drug like morphine will reduce pain (measured by using placebomorphine), the more effective real morphine actually is. Henrich, Joseph. (p. 273)

He goes on to discuss further dimensions of this, such as certain placebos for reducing blood pressure not working as well in Germany as in other countries, while those for ulcers worked better in Germany than in other countries. He states that Germans care a great deal about low blood pressure compared to other countries, which must affect the results.