dannnex

Really really strong painkiller that is used in hospitals
supposedly gives you a pretty good high, hospitals have to screen patients to make sure they aren't faking their pain to try and get access to morphine. 

quote from WebMD:
"The most common way people describe the high from morphine is a feeling of utter euphoria, a joy exceeding any other experience they have had in life. They may also describe feelings of being protected, warm, and safe"

and your body can just like
do that on it's own
if you workout

related tip:
My weight lifting coach from a while back gave this good advice. Don't do cardio for your physical health. Too much cardio can cause your body to eat away at its protein stores (ie your muscles) for energy (not good), and not enough cardio won't have enough of an effect on your overall health. Do weight lifting for your physical health, and do mild amounts of cardio for your mental health. Cardio is the best exercise to get endorphins flowing. 

In Cross Country we do weight lifting two or three times a week, yeah. Makes sense.

Morphine was used on the field in WWII right? If I remember correctly, it was potent enough that more than two doses was lethal.