pain-killers

Does anyone know if there have been any studies attempting to quantify pain objectively or at least measure it less subjectively than asking people to rate their pain? I've said before that when I was young I began training myself to deal with pain. I've had quite a bit of success in how well I...

I have been thinking about psychoactive plant substances like marijuana (from the cannabis plant), opium and its derivatives morphine, heroine and codeine (from the opium poppy). We know what these substances do to the human system, but how did they evolve? What advantage, if any, do these...