We doctors refer to it as the placebo effect
I was reading the fine print in a ad in a magazine one time about some hair growth product (a real one requiring a prescription - that's why all the fine print) in the section talking about the clinical trials. The three groups in the trial were those given the drug being tested, those given a placebo (sugar pill) and those who received nothing. The results table for the three groups listed several before and after measurements, things like new hair growth, hair density, etc. In many of these measurements, the results for those receiving the placebo were much better than those who received nothing and in some cases, almost as good as the drug being tested!
Conclusion: all these years that medical reserachers have been looking for the magic, wonder drug -they should have been doing more testing on sugar pills!