Natural-born painkiller found in human saliva - health - 13 November 2006 - New Scientist
Saliva from humans has yielded a natural painkiller up to six times more powerful than morphine, researchers say.
The substance, dubbed opiorphin, may spawn a new generation of natural painkillers that relieve pain as well as morphine but without the addictive and psychological side effects of the traditional drug.
When the researchers injected a pain-inducing chemical into rats' paws, 1 gram of opiorphin per kilogram of body weight achieved the same painkilling effect as 3 grams of morphine.
So perhaps "kiss it better" DOES work
But seriously I just came across this article looking for something else and the possibilities of a brand new painkiller that might also be an antidepressant - and is a natural substance found in our own bodies - is just fantastic.