Predictably Irrational author Dan Ariely used to enjoy taking Airborne, until he read reports that it didn't prevent colds. Before he read the reports, he was "97.5% sure" Airborne didn't work, but that tiny bit of doubt was enough for the placebo effect kick in. The news reports killed the placebo effect. He was sad that he didn't have a cold placebo to depend on, but his mother recently sent him a new nostrum and he is happy again. (I think it is Oscillococcinum, a homeopathic "medicine.").