Yes, Running Can Make You High

The runner's high: Every athlete has heard of it, most seem to believe in it and many say they have experienced it. But for years scientists have reserved judgment because no rigorous test confirmed its existence.

Yes, some people reported that they felt so good when they exercised that it was as if they had taken mood-altering drugs. But was that feeling real or just a delusion? And even if it was real, what was the feeling supposed to be, and what caused it?

Some who said they had experienced a runner's high said it was uncommon. They might feel relaxed or at peace after exercising, but only occasionally did they feel euphoric. Was the calmness itself a runner's high?

Often, those who said they experienced an intense euphoria reported that it came after an endurance event...

The New York Times: Yes, Running Can Make You High