As the medical anthropologist Daniel Moerman has documented, one of the important determinants of a drug’s efficacy is the colour of the pill it comes in. When people suffering the symptoms of depression are given the same drug in different colours, they are most likely to get better when the pill is yellow. Sleeping pills, by contrast, tend to be more effective when they’re blue.
Excerpt from: Born Liars: Why We Can’t Live Without Deceit by Ian Leslie