I strongly agree with this! for me it's riding my bicycle, your body naturally produces endorphins when you exercise which are 10 time more powerful than any drug, and can even be more addictive than ****** which is why some people get addicted to running or lifting weights, fortunately these are all good for you, for the most part what the endorphins do is stabilize your moods and give you a very strong feeling of well being, the added advantage is the exercise also get's you into shape, helps you loose weight and makes you live longer, all of which make you a happier person