Shalane Flanagan and Amy Cragg are Olympic distance runners headed to Rio this summer, and, as such, they’re ridiculously inspiring. Flanagan has made the Olympic squad four times; Cragg beat Flanagan in a harrowing trials marathon in February. They’re also endorsing Hotshot, a drink that purports to prevent muscle cramps before, during, and after workouts. “Since I started taking Hotshot, I haven’t had any cramping,” says Flanagan.

Like many supplements that claim to enhance performance, Hotshot comes with a science-based explanation (muscles don't cause cramps; nerves do), a Nobel laureate inventor, and an aggressive marketing campaign. It's hard not to be skeptical: Maybe it’s the placebo effect or a fluke, correlation doesn’t imply causation, and so on. But many elite, successful athletes use dietary supplements, aspirational taglines and all. So how do Olympians choose which are bunk, and which are worth it?

Carefully. The supplements industry is a multi-billion dollar business, and it’s sketchy: Products aren’t approved by the FDA, so it’s hard to know what’s in them. Sometimes, athletes will take a company’s “proprietary blend,” then fail a doping test because the supplement contained a banned substance. More often, says Bill Campbell, director of the University of South Florida’s Performance & Physique Enhancement Lab, the blends contain effective ingredients, but at dosages too small to do anything. “I always assume supplements don’t work,” he says, “because most don’t.”

So why take supplements? Because some of them—precious few, but still—do help performance. “In the supplement world, if you see huge effects, something’s wrong,” says Abbie Smith-Ryan, a sport nutrition scientist at UNC Chapel Hill. Instead, supplements have small effects even if they’re working properly. Maybe the creatine you take will help you heft a weight a tad longer, or that caffeine will get you off that starting block a smidge faster. That can mean the difference between a gold medal and no medal. “You try to control what you can control,” Flanagan says. And if everyone else is taking them, why not you? It’s an arms race as much as it is a legs race.

Some supplements actually have some science behind them. Researchers can test products with randomized double blind studies to control for the placebo effect, and try to keep the subjects’ schedules as similar as possible.

Hotshot

Often, though, they perform the studies on college students, who don't always stick to a regimen or, say, refrain from drinking. (Elite college athletics also is big business, and coaches might be wary of using players as guinea pigs, says Andrew Jagim, a sport scientist at the University of Wisconsin La Crosse.) The subjects of a given study are similar, of course—members of a football squad, perhaps—but then it’s hard to say whether the results apply if you’re not a 20-year-old running back. “Extrapolating to a higher level is kind of a leap of faith,” Jagim says. And no supplement is a panacea—what works for a weightlifter might not help a distance runner.

So what’s a pro athlete to do? Be very, very pragmatic. “My job is to cover a lot of miles really fast,” Flanagan says. “I don’t get too bogged down in the science.”

That means take whatever works. Cragg checks the labels of anything she tries to make sure the ingredients are as natural as possible. But it’s largely a matter of trying something before a run and seeing how she feels—supplements are so individualized that she essentially must experiment to see what works. Taste is also key: “I pick what tastes good two hours into a run,” Cragg says—otherwise, it’s hard to get whatever she’s taking down at all.

So where does that leave Hotshot? Both Flanagan and Cragg say they were initially skeptical, but the drink's promise—no more debilitating, race-losing cramps!—seemed too good to pass up. Hotshot contains spice extracts, which the inventors say activate certain nerve receptors in the mouth that signal the spinal cord to stabilize the overexcited nerve causing a cramp. That mechanism is plausible, says Ardem Patapoutian, a neuroscientist at the Howard Hughes Medical Institute who studies the ion channel Hotshot supposedly targets. "The role of sensory feedback in many physiological processes has been under-studied and under-appreciated," he says—cramping included.

More studies—beyond the ones the company has run on its own—might bear this out. But for Cragg or Flanagan (who are also, by the way, being paid to promote Hotshot), the spicy supplement is good enough. And if either of them win in Rio, they'll probably thank Hotshot because, hey, something worked.