Personally, I know the placebo effect works, I have used it on several people, coming up with some bs story about how a certain combination of honey, ginger, citrus, whisky, tea or whatever else I think of at the time was what my gran always used to make for my mum and then my mum for me when I had a cold/sore throat/tiredness etc and it usually works.
Also for myself always a litre of fruit juice, a packet of lockets and a few lemsips guaranteed to kill a cold, especially if you throw in an extra hot chilli con carne to sweat the bugger out!
The strange thing is that it still works for me even though I know it's a placebo, and I can therefore at a pinch imagine myself taking it and still feel the effects at a reduced level!
If you can fill the unforgiving minute,
With sixty seconds worth of distance run,
Yours is the Earth and everything that's in it,
And - which is more - you'll be a man my son.