Despite persistent controversy, the popular body-building supplement creatine is safe, effective, and has no known side-effects, scientists have found.
Creatine is a naturally occurring substance contained in meat and fish that plays a critical role in muscle function.
It’s long been known that the body needs about 2-4 grams of it per day, either through the diet or through synthesis in the liver from common amino acids. But starting in the early 1990s, scientists, coaches, and athletes got to wondering if consuming more than the normal amount might be a formula for increasing strength, power, and muscle mass.
That sparked a number of studies, including a 2020 paper in the journal Nutrients that found that creatine supplementation, combined with traditional strength training, allowed test subjects to build more muscle mass and lift heavier weights than people receiving the same training but taking a placebo.
Multiple sports authorities, including the Australian Institute of Sport and the U.S. Anti-Doping Agency, are now convinced of its usefulness, recognizing it as a dietary supplement that not only works, but (so long as it isn’t contaminated with something else) is legal under anti-doping rules. Nevertheless, it has a history of controversy.
That, says Richard Kreider, director of the Exercise & Sport Nutrition Lab at Texas A&M University, is because, despite repeated studies showing that creatine has no known short or long-term health risks, the Internet keeps producing rumors that it has unpleasant side effects, such as bloating, weight-gain, muscle cramps, and diarrhea. (There is even a rumor, now debunked, that it causes hair loss.)
The main problem with such rumors is that on any given day, a significant fraction of everyone experiences some of these symptoms. And people, being people, will always try to attribute them to something.
In an attempt to get to the root of this, Kreider’s team conducted a meta-analysis of 685 clinical trials involving more than 25,000 participants. Their findings, published this April in the Journal of the International Society of Sports Nutrition, found that such side effects were reported by a little more than one-eight of people taking placebos (13.2 percent, to be precise), and only slightly more (13.7 percent) of those taking creatine.
Not only is this difference statistically insignificant, it is very small. “There’s absolutely no data supporting any negative side effect anecdotally reported about creatine on the internet and in the media,” Kreider said in a statement.
Initially, Kreider told Cosmos, interest in using creatine was limited to bodybuilders and athletes in sports that require sudden bursts of power. That’s because creatine works through what is known as the ATP-phosphocreatine system, in which a molecule called phosphocreatine is built from creatine and phosphate. That molecule then helps muscles build a substance called adenosine triphosphate (ATP), which is what they use to store energy for immediate use.
It’s a fast, powerful process.
But even with creatine supplantation, muscles only have enough phosphocreatine to last a few seconds. After that, they have to build ATP via other processes. That’s why athletes, coaches, and scientists initially thought creatine wasn’t of much use in endurance-related sports.
But, Kreider says, more recent research has shown that endurance athletes such as marathoners, triathletes, and cyclists, can also benefit. In part, he says, that’s because creatine appears to help with carbohydrate loading—a process in which endurance athletes prepare for races by consuming high-carbohydrate diets in the hope of increasing their stores of this critical fuel source on the eve of big races. Creatine, he says, increases the amount of carbohydrate drawn into muscle cells during carbohydrate loading.
Another advantage, he says, is that creatine helps give distance runners the power they need for short, fast bursts of speed. Such speed bursts, says USA Track & Field coaching instructor Scott Christensen, are designed to help build runners’ maximum sprint speed, something French exercise physiologist Véronique Billat says is critical for producing a “speed reserve” that allows them to be more efficient at longer, slower distances.
Creatine also appears to speed up recovery. A study by Kreider’s one-time postdoctoral researcher, Matthew Cooke (now at Swinburne University of Technology) found that distance runners using creatine had less muscle damage, and recovered more quickly, than 30-kilometer runners not using it.
Creatine is not the only high-profile supplement scientists and anti-doping agencies find to be safe, effective, and legal. The USA Anti-Doping Agency, for example, gives positive reviews to tart cherry juice (for sleep), and watermelon juice (for post-workout recovery).
But two other high-profile supplements in the current trifecta of popular, effective, legal, and widely recognized as safe are beetroot juice and sodium bicarbonate.
Beetroot juice is simply juiced beets, with the fiber strained out. It tends to be sold in concentrated form, with doses akin to eating 200-300 grams of beets a day.
“[Beetroot juice] is one of the more promising [supplements],” says Kreider, who in addition to his work on creatine is a co-founder of the International Society of Sports Nutrition (ISSN). “We actually have a position stand we’re about to come out with on beetroot,” he says.
Of particular interest, he says, is its value both as an anti-inflammatory (speeding recovery from hard workouts) and as an aid in hypoxic environments—meaning high elevations.
Part of its value may be that it is rich in nitrates. “For a long time, the American Heart Association has recommended diets high in nitrate,” Kreider says. One major source of them is spinach. “If you remember Popeye [the cartoon character whose strength came from spinach], this actually has ergogenic benefits because of those nitrates.” But another good source is beets.
The reason is because nitrates quickly convert to nitric oxide, the same substance used by nitroglycerin tablets to help cardiac patients ward off incipient heart attacks. “Nitric oxide causes vasodilation [widening of blood vessels] and more oxygen availability,” Kreider says.
The main downside is anecdotal reports of GI distress, though, as with creatine, Kreider says, there is no consistent evidence for side effects other than the potentially alarming discovery that you can wind up with a red stool. “That is just the natural [red] dye coming out,” he says.
That said, “everyone will be a little bit different,” he says. “The rule of thumb is if you are going to use [something] for competition, always practice it during training.”
Sodium bicarbonate is the latest major player on the scene. It’s long been used for treating indigestion, and is the same thing as baking soda, which is used in a wide variety of foods.
The theory is that it is mildly alkaline, which means that consuming it at the optimum time prior to a race or workout might help counteract muscle-fatiguing acidosis created by hard exercise. “There are studies out of New Zealand that show that it has benefit on high-intensity performance in the 2-4 or 5-8 minute range,” Kreider says.
It can also be useful at the end of something like a long bicycle ride, he says, “[when] you’re sprinting to the end to try to win.”
Other supplements that might to be safe and effective are described in review papers periodically published by the ISSN. The most recent was in 2025, but, Kreider says, an update is in process.