Can Exercise Make You High?
In a way, yes. Researchers have discovered that exercise, and specifically high-intensity activities like running, produces increased levels of endocannabinoids in the bloodstream. Endocannabinoids are the body’s natural form of marijuana, also known as cannabis. Cannabis is composed of cannabinoid molecules which bind to receptors in the brain, thereby reducing anxiety and producing a high or feeling of euphoria. These molecules are also naturally produced when people exercise, which explains the “runner’s high” that many experience post-workout.
Until the 1980’s, scientists believed that endorphins, the body’s natural painkillers, were responsible for producing the runner’s high. They came to this conclusion because research showed that high levels of endorphins are present in the bloodstream after exercise. However, endorphins are too large to cross the blood-brain barrier, so they can’t be responsible for the high.
In 2003, scientists discovered that the endocannabinoid system plays a major role in producing runner’s high. Researchers at the Georgia Institute of Technology had college students run on a treadmill or use a stationary bike for 50 minutes. They found that after exercising, the students’ blood had increased levels of endocannabinoid molecules (Sparling, Giuffrida, Piomelli, Rosskopf, & Dietrich, 2003). These molecules, which are mainly composed of lipids, are small enough to cross the blood-brain barrier.
Since 2003, many additional studies have been conducted on the relationship between the endocannabinoid system and exercise. In 2010, French researchers bred mice (who naturally enjoy running) without an endocannabinoid system. The mice ran half as often as mice with functioning endocannabinoid systems. The researchers hypothesized that endocannabinoids must also play a role in motivation to exercise (Dubreucq, Koehl, Abrous, Marsicano, & Chaouloff, 2010).
A study conducted this year in Germany measured the anxiety level of mice before and after running on a wheel. After the mice ran, their blood had higher levels of both endorphins and endocannabinoids. The mice were also calmer and more tolerant to pain. The researchers then repeated the experiment but blocked the endocannabinoids from binding to receptors in the brain. This time, the anxiety level and pain tolerance of the mice did not change after they ran on the wheel. When the researchers replicated the experiment a third time, they blocked endorphins from binding to receptors, and yet the mice still displayed lower levels of anxiety and higher levels of pain tolerance after running (Fuss, Steinle, Bindila, Auer, Kirchherr, Lutz, & Gass, 2015).
Interestingly, exercising at high altitudes produces higher levels of endocannabinoids. In 2012, researchers studied three groups of Italian mountain climbers. The first group hiked at a low altitude, the second group went on a similar hike at a high altitude, and the third group took a helicopter to a high altitude. The hikers were given blood tests at various points to determine the levels of endocannabinoid in their blood. While endocannabinoid levels were high in the first two groups (but not the third), the second group had higher endocannabinoid levels than the first. The researchers suggested that endocannabinoids help human beings adapt to both physical and emotional stress. Hiking at a high altitude makes exercise harder, which puts greater stress on the body, therefore producing higher levels of endocannabinoids (Feuerecker et al., 2012).
In addition to these empirical studies, there is plenty of anecdotal evidence linking the endocannabinoid system to runner’s high. The runner’s high is often described as “pure happiness, elation, a feeling of unity with one’s self and/or nature, endless peacefulness, inner harmony, reduction in pain sensation, and boundless energy” (Dietrich & McDaniel, 2004). These descriptions are extremely similar to the way people describe the high from marijuana. Surprisingly, research shows that the cognitive changes that result from using marijuana, such as deficits in attention and working memory, also occur temporarily during long sessions of running and cycling. However, scientists caution that such evidence is merely anecdotal and that more controlled studies must be conducted before conclusions are drawn.
Much of the research on the endocannabinoid system focuses on running, but what about other forms of exercise, like swimming or weightlifting? Dietrich and McDaniel (2004) suggest that these forms of exercise may not have the same pain-relieving qualities as running because the endocannabinoid system kicks into high gear when the skin is activated by painful stimuli, like when feet pound the pavement during an intense run. This does not mean that the endocannabinoid system is not activated at all by other forms of exercise, but rather that it may not be activated to the same extent. However, further research is needed to determine which forms of exercise stimulate the endocannabinoid system, as well as the duration for which exercise must be performed.
Although there is still plenty to learn about the endocannabinoid system and its role in the body, perhaps the lure of a natural high will serve as an alternate motivation for people to begin an exercise regimen.