Can Pre-Workout Cause Stomach Problems? (Bloating & Nausea)

Benedict Ang, CPT, PN1-NC
Published by Benedict Ang, CPT, PN1-NC | Staff Writer & Senior Coach
Last updated: February 19, 2024
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As a personal fitness coach, I spend many hours a week working with clients at the gym and guiding them toward their fitness goals. Their exercise routine is only part of their plan. We also discuss their food habits and dietary supplements.

Pre-workout supplements are popular for many gym-goers to boost energy, endurance, and recovery, but some experience stomach issues and wonder if their pre-workout is the culprit.

I consulted our medical professional and looked at common ingredients found in pre-workout supplements to determine if they could cause stomach problems.

Here’s what I found.

Quick Summary

  • Pre-workouts can cause stomach problems as they contain certain ingredients like magnesium, caffeine, sodium bicarbonate, and caffeine.
  • Diarrhea, bloating, and stomach upset are some of the stomach problems you risk suffering.
  • According to the Harvard School of Public Health, the global pre-workout supplement market was estimated at $13.98 billion in 2020 and is projected to reach $23.77 billion by 2027, reflecting the growing popularity of these supplements.
  • In my opinion, it's crucial to choose pre-workouts carefully and consult a doctor for any adverse reactions to ensure both physical and digestive health.

Can Your Pre-Workout Be Causing Stomach Problems?

A person holding his stomach due to pain

Stomach issues from pre-workouts may be due to ingredients like magnesium, sodium bicarbonate, caffeine, and creatine.


Our team discovered through the National Library of Medicine and using this product that magnesium, while vital for energy metabolism and muscle function, can cause side effects like diarrhea and stomach cramps [1].

Adverse effects of magnesium as a pre-workout, particularly magnesium citrate supplementation, include diarrhea, stomach cramping, and nausea [2].

Sodium Bicarbonate

The National Library of Medicine says that sodium bicarbonate, also known as baking soda, may enhance exercise performance [3].

However, baking soda as a pre-workout can cause nausea, vomiting, stomach cramps, and loss of appetite, but this generally occurs only when taken at high doses [4].


After putting it to the test, we found that caffeine, despite its benefits in boosting energy and performance, can lead to gastrointestinal issues such as acid reflux and stomach upset. The National Library of Medicine also confirms it [5].

Gastrointestinal side effects of caffeine include acid reflux, stomach upset, abdominal pain, or diarrhea which can lead to dehydration [6].


The National Library explains that creatine is as popular as caffeine as an ingredient in pre-workout supplements because it can be highly effective at improving athletic performance and endurance, as well as promoting muscle recovery [7].

The most frequent negative effects of creatine supplementation are stomach upset and diarrhea [8].


L-arginine, an amino acid precursor to nitric oxide, is added to pre-workouts to increase nitric oxide levels and boost pumps [9].

Mayoclinic suggests that L-arginine supplementation can have a negative impact on the gastrointestinal system by causing bloating, diarrhea, abdominal pain, and nausea [10].

“Caffeine is a fairly safe supplement at the recommended doses. It may cause minor side effects in some people and should be used with caution in individuals with heart disease, high blood pressure, GERD, and several other conditions.”

- Rudy Mawer, MSC, CISSN

How to Reduce Stomach Issues

A woman doing crunches

Exercise is essential to physical health and to combat stress, anxiety, and depression [11].

Any adverse effects from pre-workouts, like stomach upset, bloating, and diarrhea, can inhibit your ability to work out, which can be detrimental to your physical and mental health.

I usually tell my clients a few things they can do to reduce gastrointestinal issues caused by pre-workouts:

  • First and foremost, consult your doctor to discuss any adverse reactions or underlying medical conditions before starting any new supplement.  Additionally, avoid proprietary blends which lack transparency about ingredients and dosage. Knowing precisely what you are consuming is critical to putting your mind at ease concerning health risks.
  • Follow the manufacturer’s directions when mixing your pre-workout supplement. Not using enough water and consuming a concentrated liquid can lead to an upset stomach and diarrhea.
  • When it comes to label reading, look for independent lab testing stamps that will validate the quality of the product. Some examples of separate testing facilities are NSF International,, and USP.
  • Be aware of any ingredients that affect you negatively, and avoid them. For example, if you are sensitive to caffeine, plenty of caffeine-free pre-workouts are available.

Other Side Effects

Man experiencing stomach pain

Digestive system issues are not the only side effects of pre-workout intake. Digestive system issues are not the only side effects of pre-workout intake.

After consumption, some people experience pre-workout tingles due to the addition of beta-alanine and amino acid that reduces acidity in muscle tissue.

Beta-alanine helps reduce fatigue, increase endurance, and promote muscle growth. Though not harmful, this tingling sensation is bothersome to many individuals.

A report from the National Library of Medicine inquires that many of my clients believe their pre-workout supplement hinders their weight loss efforts, but It is not uncommon for the top pre-workouts that contain creatine to cause water retention [12].

The scale's extra pounds? Probably just water. Also, these supplements often pack a caffeine punch, potentially pushing you past the 400 mg daily caffeine limit, especially when combined with your usual coffee or soda.

Besides stomach problems, caffeine can cause increased blood pressure, possibly leading to heart palpitations and even an increased risk of a heart attack [13]. 

Some users experience pre-workout itching or burning sensation of the skin, likely due to the addition of niacin (B3), which increases blood flow, causing a rush of blood to the skin's surface, and resulting in skin flushing [14].

We know finding the right supplement is tricky, which is why we have tested and reviewed dozens of products:


Can Pre-Workouts Affect IBS?

Yes, pre-workouts can affect IBS and trigger symptoms. Many people with IBS follow a low FODMAP diet. FODMAPs are a group of compounds believed to trigger IBS and other digestive problems.

Some pre-workout ingredients, like artificial sweeteners, are considered high FODMAP.

Should I Take Pre-Workout on an Empty Stomach?

Yes, pre-workout on an empty stomach allows it to enter the bloodstream much quicker, so you feel the effects quicker.

On the flip side, you may have an increased risk of digestive issues when taking on an empty stomach.


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