It would be pretty great if watching an episode of Silicon Valley were as effective at relieving a headache as over-the-counter painkillers. And while researchers don't go that far, they have found that genuine laughter does indeed increase a person's tolerance for pain. In the study, which was released in a 2011 issue of Proceedings of the Royal Society B, researchers had participants watch episodes of South Park, Friends, The Simpsons or stand-up clips from celebrated comics. These participants were exposed to pain (in the form of a tight blood-pressure cuff, a cold wine sleeve on the arm, or a wall sit — when you sit against a wall on an imaginary chair, holding your legs at a 90-degree angle, and your legs really, really burn ) and tested and how well they handled it pre- and post-laughter. "The results confirmed that when laughter is elicited, pain thresholds are significantly increased, whereas when subjects watched something that does not naturally elicit laughter, pain thresholds do not change (and are often lower). These results can best be explained by the action of endorphins released by laughter."
That last point is key: it had long been accepted by scientists that laughter helps people tolerate pain, but was that benefit from the laughing itself, or the positive feeling that resulted from laughing? After exposing some of the study participants to feel-good, but not funny, content (like the beloved documentary Planet Earth) the researchers saw that only the laughing participants had increased pain thresholds. They found that the physical act of laughing released endorphins, which "play a crucial role in the management of pain."