Well, that's one of the reasons why homoeopathy has not been able to be validated by science yet. Science is more or less ill-fitted to verify the efficacy of methods in which their efficiency depends on the taker, or where results depend on the observer.
Scientific bias shows its head in these cases: because it's difficult to prove it, the assumed stance that it doesn't work is the one that is pushed through. Once scientists start noting a significant amount of people for whom it works, then they will start shifting their biases and review the uncertainty in a positive light. I hope. :)