The grueling sport of ultramarathon has fostered a mingling of two seemingly opposite camps: endurance jocks and potheads. 

“If you can find the right level, [marijuana] takes the stress out of running,” says Avery Collins, a 22-year-old professional ultramarathoner. “And it’s a postrace, post-run remedy.”

The painkilling and nausea-reducing benefits of marijuana may make it especially tempting to ultramarathoners, who compete in races that can go far longer—and be much more withering—than the 26.2 miles of a marathon. Ultramarathon is one of the fastest-growing endurance sports; there were almost 1,300 races in the U.S. and Canada in 2014, up from 293 in 2004, according to UltraRunning Magazine.

Ultramarathons last anywhere from 30 to 200 miles, and typically crisscross mountainous terrain and rocky trails. Runners endure stomach cramps and intense pain in their muscles and joints. Competitors often quit after a sudden loss of motivation, matched with the boredom of running for upward of 24 hours straight.

“The person who is going to win an ultra is someone who can manage their pain, not puke and stay calm,” said veteran runner Jenn Shelton. “Pot does all three of those things.”

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