Your Pre-Workout Supplements Might Contain Some Shady Ingredients

“Many claims on supplement labels are usually, if not always, based on exaggerated research findings."
Tattooed woman working out in the gym
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Gym chatter would lead you to believe that getting in a good workout is simply impossible without “pre-workout”—often, a powdered or liquid concoction that promises to give you more energy and thus improve your performance in the gym.

Dozens of companies have their own unique blends of pre-workout, each one bearing catchy, attention-grabbing names and labels. But marketing aside, pre-workout supplements are thorny in that they all contain different ingredients and in different amounts. Saying you’re taking a pre-workout supplement is kind of like saying you’re drinking a smoothie: Does it have protein powder? Fruit? Yogurt? The term has become a catch-all.


“A pre-workout supplement has no distinct definition, but the ultimate purpose for their use to is to temporarily enhance or ‘boost’ performance [during] exercise, usually 10 to 30 minutes after supplementation,” says Edward Jo, director of the Human Performance Research Lab at California State Polytechnic University.

The underlying rationale being that if you train harder and put in better quality workouts, you ultimately get more out of those workouts. What exactly those results are varies product to product, but across the board, they tend to promise improved power, strength, and endurance, says Andrew Jagim, assistant professor of exercise science Lindenwood University in Missouri. Jagim notes that some are more interested in strength adaptations over cardio, fat loss, or muscle recovery.

“With that said, most pre-workouts contain stimulants—namely, caffeine,” Jo says. “Other common ingredients such as creatine, beta-alanine, and various amino acids do not necessarily function well as a pre-workout since they are not stimulants, but they may be effective at improving performance if they are supplemented over time consistently.”

Which pre-workout ingredients are the most effective?

“Many claims on supplement labels are usually, if not always, based on exaggerated research findings,” Jo says. There are, however, several ingredients that show promise of real-world significance, he says.

The first is tried-and-true caffeine. An established central nervous system stimulant, caffeine works by blocking adenosine molecules from binding to their receptors. Adenosine basically tells your brain that you’re sleepy, so blocking those receptors can make you feel more energetic, Jagim says. Plus, when adenosine builds up in your blood—like when caffeine keeps it floating around in your bloodstream—it leads to an adrenaline release that even further revs up your workouts.


Studies have shown that consuming between 0.15 grams or 0.09 grams of caffeinated coffee per kilogram of body weight can improve performance during a workout. And according to a 2018 review of multi-ingredient pre-workout supplements, tubs that contain at least 300 mg per serving are most effective. That works out to about the equivalent of three to five cups of coffee, depending on your brew, Jagim says.

Some people, however, don’t handle their caffeine all that well, says Marie Spano, a registered dietitian and sports nutritionist for the NBA’s Atlanta Hawks. “Too much caffeine can be detrimental—they feel too jittery to really perform. Emerging evidence also suggests genetic variations in caffeine metabolism. For some, caffeine may actually lead to worse performance.”

After caffeine, creatine is the most commonly contained ingredient within pre-workout supplements, and it’s one that’s met with wide approval across the sports community. “Creatine has become a staple of sport supplements,” Jo says. “About 70 percent of the research on creatine has demonstrated some level of efficacy. Therefore, as scientists, we can say with good reasoning that creatine is beneficial for performance if taken over time.”

The “over time” part is important, though. That’s because creatine—technically creatine monohydrate—converts in the body to creatine phosphate, an energy substrate that the body’s phosphagen metabolic system uses to make ATP, or energy. When taken every day for more than a couple of weeks (sometimes people take higher doses for the first few days of supplementation to “pre-load,” creatine gives the body more energy substrates to help fuel high-intensity exercise, Spano says.


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Next is beta-alanine, which is an amino acid involved in the production of carnosine, an intramuscular compound that buffers pH to mitigate muscle “burn” and help people work harder, longer, during high-intensity exercise, Jagim says. It’s a relatively new supplement for sports performance, and a 2018 review concluded that while efficacy is still up in the air, it appears to be safe over the long-term. That said, it did note acute side effects—most commonly paraesthesia—or a “pins and needles” sensation on the skin, after consumption.

Lastly, some pre-workout supplements contain other amino acids, either branched chain amino acids or outright protein, to help promote muscle recovery post-exercise. While most people consume protein after their workouts to recover, research does show that pre-workout protein can help give you a jump, Jagim says.

Which ingredients are more questionable?

When it comes to the pre-workout ingredients that might impact exercise performance, or might impact it in a “there’s statistical significance here but no real-world implication” sort of way, there are plenty.

The first are commonly called nitric oxide precursors, but usually show up on labels under branded names such as Citrulline and Nitrosigine, or as beet root or pomegranate. “Cirtulline and arginine [Nitrosigine being a branding term] are traditionally implicated as a muscle blood flow enhancer via the production of nitric oxide, which is a potent vasodilator, meaning it relaxes the arterial blood vessels,” Jo says.


“The idea is that with increased NO and vasodilation, muscles can be fed more oxygen and nutrient-rich blood during exercise,” he says. “However, the research is very mixed and inconclusive.” Studies that show benefits of citrulline and arginine tend to be on people with hypertension, Jo adds—but these ingredients don’t appear to enhance muscle blood flow during exercise, which means they’re probably not effective performance enhancers. Jagim notes that most pre-workout supplements contain NO precursors in doses that are far lower than what’s been shown to actually have an effect in those studies.

Antioxidants are another ingredient that have been recently met with debate. Of course, they aren’t listed on labels as antioxidants, but most often as some sort of fruit juice or extract, says Abbie E. Smith-Ryan, director of the Applied Physiology Laboratory at the University of North Carolina–Chapel Hill. The idea is that these will help promote muscle recovery by lessening inflammation, and while tart cherry juice does have some good data behind it, some experts are now questioning if decreasing post-workout inflammation is so wise.

Again, whether or not the supplement contains enough of a given ingredient to do any good, or just enough to make the tub’s label look sexy, is often a big question mark.

Which ingredients are potentially dangerous?

In the end, when it comes to pre-workout supplements, apart from those of caffeine, creatine, and protein, “most effects, although significant statistically, are trivial practically,” Jo says. There is still something to the simplicity of taking one rather than three supplements for your workouts, but anything else in your tub is unlikely to hurt your exercise performance or your health.

That is, of course, assuming that the product contains what it says it does and nothing else. “With any supplement, however, accurate labeling and purity is always a question since there are no strict federally mandated regulations over them before they hit the market, unlike drugs,” Jagim says.


Of particular concern is the fact that banned stimulants are too-often contained in pre-workout supplements. “For example, oxilofrine is a drug chemical that is not FDA approved and is only prescribed overseas to stimulate the cardiovascular system and increase blood pressure,” Jo says. “Since supplements do not require FDA approval, many of these pre-workouts containing oxilofrine end up hitting the market.” A 2017 Harvard Medical School study found that out of 27 pre-workout or "fat burner" supplements, over half contained oxilofrine, which was not disclosed on the label. Of these, 43 percent contained levels similar to or greater than pharmaceutical level.

“The danger here is that per instruction on these supplement labels, consumers could be taking 16 times the medically prescribed dosage of this amphetamine-like chemical without even knowing it,” Jo says. In another 2018 study, the same lab group found that in 24 "energy boosting" supplements, 20 contained unlabeled traces of higenamine, a banned stimulant that may pose high risk when taken unknowingly, Jo says.

“There is very little oversight on the accuracy of labels, thus giving rise to third party labs that provide testing and accreditation for supplement products,” Jagim adds. NSF International, Informed Choice, and USP are all highly respected organizations that test supplements to make sure that they contain what they say they do, and nothing else. To find certified supplements, go to these organizations websites for recs or look for their labels on any tubs you see in the supplement aisle. If you’re an athlete, you should also check with a program such as NSF International’s Certified for Sport to make sure that none of its ingredients would keep you from competing. Jagim also recommends checking out the sites to ID supplement companies that are consistent offenders. “Avoid any companies that have gone down that path in the past,” he says.

What’s more, Jagim recommends opting for brands that also have an “open label” policy, such as JYM Supplement Science and Kaged Muscle. “You should be able to see exactly what ingredients the supplement contains and how much of each ingredient,” he says. Ideally, levels would be high enough to have a real, in-the-gym benefit.

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