What To Do If Pre-Workouts Wreck Your Stomach

From marathon runners to weight room regulars, all sorts of exercise aficionados drink pre-workout supplements before they get sweating so they can make the most of their precious time and hit their routines hard. And while all pre-workouts are geared to help you crush it during your training session, the formulations of the many products out there vary widely.

Grab any pre-workout off the shelf and you’ll likely find it contains ingredients like caffeine (which helps you feel alert and ready to kick it), beta-alanine (which wards off muscle fatigue), amino acids like citrulline and arginine (for amped-up blood flow), and a whole slew of other potential add-ins, like creatine, betaine anhydrous, and more. Each has its role to play in helping you dominate your workout. As popular (and effective) as pre-workout supplements are, though, they are also known to cause digestive distress in some people, particularly those with sensitive stomachs. Nothing wrecks a set of squats quicker than the sudden urge to sprint to the bathroom…

Here, sports dietitians and fitness pros break down why your pre-workout might be messing with your stomach and help you troubleshoot your supplement routine so you can make gains without hurting your gut. 

• ABOUT OUR EXPERTS: Brittany Michels, M.S., R.D.N., C.P.T., is a registered dietitian and certified personal trainer with The Vitamin Shoppe. Chris Mohr, Ph.D., R.D., is a registered dietitian, exercise physiologist, and a fitness and nutrition advisor for Fortune Recommends.

Why Pre-Workout Supplements Can Mess With Your Stomach

Pre-workout users are as unique as pre-workout supplements themselves, which means that a product that works wonders for one gym-goer could spell disaster for another, according to Brittany Michels, M.S., R.D.N., C.P.T., a registered dietitian and certified personal trainer with The Vitamin Shoppe. Everybody—and every body—is different.

Of the potential ingredients featured in a pre-workout, quite a few could potentially contribute to digestive upset in certain folks, according to Michels.

1. Caffeine

In many cases, caffeine is a big one. “Caffeine naturally has stimulating effects, so, just like coffee, it may stimulate digestive movement,” says Michels. If you know that coffee typically makes you go, it’s safe to assume a pre-workout higher in caffeine will have a similar effect. 

2. Creatine Monohydrate

A common pre-workout staple, creatine monohydrate could be a culprit behind an upset stomach, suggests registered dietitian and exercise physiologist Chris Mohr, Ph.D., R.D., a fitness and nutrition advisor for Fortune Recommends. It’s notorious for causing bloating and belching. “Creatine causes a fluid shift, bringing fluids into muscle cells,” he explains. “This shift in fluid balance may cause gastrointestinal issues.”

Typically, this GI upset is temporary and occurs during a loading phase, in which exercisers take large amounts of creatine (like 20-plus grams) per day, Mohr says. This effect is usually pretty limited at lower doses (like three to five grams per day), though it’s possible you could experience issues from creatine in your pre-workout if you have a particularly sensitive stomach or are also taking separate creatine supplements.

3. Pump-Boosters Like Citrulline and Arginine

The amino acids arginine and citrulline promote nitric oxide production and increase circulation, which can be a great thing for exercise performance, says Michels. The downside? That increased circulation doesn’t just occur in your muscles; it also occurs in your digestive system, which might spur an unwanted trip to the bathroom, she says.

4. Magnesium

Magnesium is an important mineral, but depending on the form featured in your pre-workout supplement, it could stir up trouble for you. “Too much magnesium oxide or magnesium citrate may have a laxative effect,” explains Michels. Magnesium glycinate is a gentler option and comes with fewer gastrointestinal side effects than other supplemental forms. Check to see what form of magnesium your pre-workout supplement uses.

5. Sodium Bicarbonate

Sodium bicarbonate (which is added to pre-workout formulas because it buffers against lactic acid buildup in the muscles, potentially improving endurance and delaying fatigue) is another ingredient that can cause digestive issues, specifically bloating and discomfort, agree Michels and Mohr. 

“Because it is alkaline, it can react with stomach acids and cause gastrointestinal issues like gas and bloating, so too much can have unwanted side effects like GI distress,” Mohr explains.

6. Certain Sweeteners

Finally, the type of sweetener a pre-workout uses to make all of those oomph-boosting ingredients delicious to drink down may be the culprit behind the GI distress you experience after chugging, suggest Michels and Mohr. Artificial sweeteners and sugar alcohols (which are not well digested by the body) can both have this effect. 

How To Troubleshoot Your Pre-Workout Routine

Figuring out which pre-workout formula works best for you will take a little trial and error. After all, everyone’s body reacts differently to various compounds, so what works for one person might not be best for another, says Mohr. That said, we’ve got a few simple steps that’ll help you navigate the process. 

1. Start with an entry-level option

“If you have never tried a pre-workout before, consider grabbing one with low doses of common digestive-offending ingredients,” recommends Michels. That might look like fewer than 150 milligrams of caffeine, fewer than two grams of creatine, and fewer than 2,000 milligrams of citrulline and/or arginine. 

“Intense, highly-concentrated supplement formulas can be tough on the stomach, especially if someone is not used to them,” agrees Mohr. If you’re a newbie—or know you have a sensitive system—do yourself a favor and ease in gradually.

2. Consider past experiences

If you have some experience with various sports supplements or stimulants, they can help you gauge what to look for and avoid in a pre-workout supplement that won’t wreck your stomach.  “Be mindful of ingredients you’ve had tolerance issues with in the past,” Michels says. 

For example, “Choose stimulant-free supplements or options with fewer stimulants if caffeine bothers you,” says Mohr. Or, if you’ve dabbled in standalone creatine or pump-boosting amino supplements and it didn’t go smoothly, look for a pre-workout that contains smaller amounts of those ingredients—or omits them completely. 

On the flip side, if you’ve had positive experiences with certain ingredients or pre-workout formulas, look for similar specs when shopping for a new brand to try, suggests Michels. 

3. Start low and go slow

“If you’re unsure which ingredients have caused issues, either find a pre-workout option with lower dosages of potentially gut-impacting ingredients to test your tolerance,” Michels says. If all goes well, you can always switch to a higher-stim or otherwise more concentrated formula.

If you do go for a higher-intensity product right off the bat, test how you feel on just half a serving (or even less!) during your next workout, Michels suggests. Find an amount your body tolerates and slowly increase from there over the course of weeks.

4. Stay Hydrated

How you take your pre-workout is also important for feeling your best on it. Staying properly hydrated is key because substances found in pre-workout supplements (like creatine and sodium bicarbonate, respectively) affect your body’s fluid and electrolyte balance, explains Mohr. “Maintaining proper hydration status helps support the outcomes of your supplements,” he says. For this reason (and the fact that proper hydration supports focus, accuracy, and overall performance), Mohr recommends drinking plenty of water before, during, and after your workout.

5. Time Your Consumption Well

Another must-do: “Take your pre-workout 30 to 60 minutes before exercising to give your body time to process it,” shares Mohr. “This timing allows your body to fully process the supplements,” he explains. Ingredients like caffeine, creatine, and beta-alanine, in particular, need this much time to peak in your bloodstream, at which point they’re most useful in increasing your energy and performance.

Final Advice

As always, “pay attention to how your body feels,” says Mohr. “If a product consistently causes issues, try a different one—or boost your energy with a small snack instead.” (Here are some options fitness pros love.)

And lastly, be patient! The right formula for you is out there; it may just take some experimentation and really close communication with your body to figure out which pre-workout will help you maximize your training time without destroying your digestive system.