Elle Woods of Legally Blonde once proclaimed: “Exercise gives you endorphins. Endorphins make you happy. Happy people just don’t shoot their husbands.” Can’t argue with that logic, right? Problem is, this iconic quote is based on outdated scientific assumptions about endorphins.
As Gretchen Reynolds writes in the New York Times, “endorphins may be unfairly hogging the credit for making workouts enjoyable.” Scientists actually realized some time ago that endorphin molecules, which are known to have pain-relieving properties in the muscles, are too large to pass through the blood-brain barrier; since then, research studies have been trying to determine which other substances could be responsible for the positive mood changes that originate in the brain. Endocannabinoids, the naturally-synthesized compounds that activate the same receptors as marijuana, are an obvious candidate to study in attempting to crack the mystery of “runner’s high.”
A recent study used lab mice to parse the effects of endorphins vs. endocannabinoids on post-run anxiety. They found that when endocannabinoid receptors were blocked in mice, they no longer exhibited their usual chill demeanor after running. On the other hand, when endorphin response was blocked in the mice (while the endocannabinoid system was left alone), the mice had less anxiety and were less sensitive to pain. This strongly implicates endocannabinoids, and not endorphins, as the main contributors to runner’s high. As Reynolds reminds us, there are some important things to consider before drawing conclusions; for one thing, is it too early to extrapolate these findings to humans. For another, we may need to run a whole lot in order to feel these effects (the tiny mice in the study ran an average of three miles a day). For now, this new research may be just another step to uncovering the full extent of the cannabinoid system’s role in making us feel calmer and happier.