Workout supplements containing caffeine can be dangerous, experts say. They can cause irregular heartbeats and overheating.

• One of the most common ingredients in sports supplements is caffeine.
• In moderate amounts, caffeine can boost performance in some sports, depending on the individual athlete.

Taking a new supplement to get faster gains in the gym or perform better at your sport can be tempting. Sports supplements including "pre-workout," protein powder, and various pills have become popular ways for some people to boost their workout routines.

But Stefan Pasiakos, director of the National Institutes of Health Office of Dietary Supplements, told Business Insider that "there needs to be better appreciation and attention toward anything that is supposed to be stimulant related, " including sports supplements that contain caffeine.

That's because, in large doses taken quickly, the caffeine in sports supplements can cause dangerous health effects including nausea or vomiting, irregular heartbeats, and even death.

Some caffeine can enhance athletic performance

Moderate amounts of caffeine have been shown to boost performance.

"Caffeine for the most part is pretty innocuous," Bill Gurley, principal scientist in the National Center for Natural Products Research at the University of Mississippi, previously told Business Insider.

Having a little caffeine before a workout, like a cup of coffee or green tea, could enhance your performance and even make working out more enjoyable.

In 2021, the International Society of Sports Nutrition concluded that ingesting caffeine appeared to be most beneficial for aerobic endurance sports like cycling, running, and swimming. The benefits also largely depended on the individual athlete, genetics, and lifestyle factors.

The most beneficial dose was found to be between 3 and 6mg of caffeine per kg of body weight. For someone who weighs 150 pounds, that would be roughly 200-400mg of caffeine or about two to four cups of coffee.

But consuming caffeine past this amount hasn't been found to boost athletic performance further, and could harm your health.

Too much caffeine can be risky

When the amount of caffeine consumed surpasses 400mg, things can get risky— even for otherwise healthy people. Too much caffeine can lead to vomiting, cramps, and a fast, irregular heartbeat. At very high doses, it can cause a loss of consciousness and death.

In 2018, a man in Australia died after drinking a highly caffeinated protein shake.

In 2021, a 20-year-old said she had a heart attack after swallowing a dry scoop of a highly caffeinated pre-workout supplement.

One of the problems with sports supplements, Gurley said, is that "you can get a lot of caffeine really fast."

It's also easier to overdose on caffeine in supplement form since you only need to take one to two pills or a scoop of powder, compared to drinking 15 cups of coffee.

Caffeine in supplements can lead to overheating

Using stimulants, including supplements that contain caffeine, can also make it harder to tell if you're becoming overheated. It's a risk that's amplified when people take stimulants and do strenuous exercise or exercise in hot or humid conditions.

"Exercise alone puts a significant strain on your cardiovascular system," Gurley said. "Then you throw in a bunch of stimulants that are known to have adverse cardiovascular effects, and it's just a bad combination."

Exercise supplements aren't as regulated as prescription drugs

Another problem, both Gurley and Pasiakos said, is that workout supplements often contain many different ingredients, and don't have to state exactly what's in them. That's because supplements aren't regulated as strictly as prescription medications.

"There's a variety of products out there that claim to boost performance, boost energy, and a lot of them have proprietary blends," Pasiakos said. But products that contain proprietary blends "don't have to state what's in those."

So if you plan to start a new exercise routine soon — or just continue an old one — think before picking up a workout supplement full of caffeine.

"When I was younger, I would try all sorts of purported performance-enhancing supplements, most of which contained some sort of stimulant," Pasiakos said. "However that's changed, and I know there is no substitute for good nutrition, exercise, and sleep."