Opioids
The body's own painkillers, endorphins among them, working on the same receptors as morphine. They damp pain and play a part in pleasure; the runner's high they get credit for does not seem to need them.
Your body makes its own opioids: short protein chains, produced mainly in the brain, spinal cord and pituitary gland, that act on the same receptors as morphine and heroin. Evidence: solid The first were identified in 1975. Evidence: solid There are three main families: endorphins, enkephalins and dynorphins. Evidence: solid Their best-known job is damping pain, especially under stress or injury; they also play a part in reward, mood and the stress response. Evidence: solid
In people they can be tracked with PET scans, which follow a tracer that sticks to opioid receptors. In 12 men, half an hour laughing at comedy with close friends released the brain's own opioids in areas including the thalamus and the caudate, compared with half an hour alone, and they felt more pleasure. Evidence: decent That this binds friends over time is the researchers' theory, not a finding. Evidence: worth trying
Where it gets oversold: "runner's high is endorphins". Running raises endorphin in the blood, but endorphin in the blood doesn't cross into the brain easily. Evidence: decent A PET study of 10 athletes did find the brain's opioids released after two hours of running, and more release went with more euphoria. Evidence: decent But when 63 people ran on a drug that blocks opioids, they still got the euphoria and the calm, and their endocannabinoids, the body's own cannabis-like chemicals, rose either way. Evidence: decent In mice, the calm and the pain relief after running depended on cannabinoid receptors, not opioid ones. Evidence: decent Opioids may play a part. They're not the whole story. Evidence: decent
Why it matters
Laugh at the same thing and games night partly lean on the laughter scan: 12 men, one study. Evidence: decent In learning to dance, teenagers dancing in sync could take more pain afterwards, a rough stand-in for this system; that it does the bonding is the authors' idea. Evidence: worth trying The caudate, one of the areas in that scan, is part of the striatum. Evidence: solid