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Why does my pre-workout give me diarrhea?

Pre-workout supplements have become increasingly popular among gym-goers and athletes looking to boost their energy and performance during exercise. However, some pre-workout ingredients can cause unwanted digestive side effects like diarrhea in some people. In this article, we’ll explore why pre-workout may cause diarrhea and how to avoid it.

Common pre-workout ingredients that can cause diarrhea

Many pre-workout supplements contain large doses of ingredients like caffeine, beta-alanine, and artificial sweeteners that may irritate the digestive tract for some individuals. Here are some of the main culprits:


Caffeine is included in most pre-workout formulas for its ability to increase alertness, focus, and exercise capacity. However, at the high doses found in pre-workout (often 200-400mg per serving), caffeine can overstimulate the gastrointestinal tract and induce diarrhea in those sensitive to its effects.


Beta-alanine is an amino acid that can enhance muscular endurance. But it can cause a tingling skin sensation called paresthesia in some people. High doses may also irritate the intestines, provoking diarrhea.

Artificial sweeteners

Pre-workouts often contain artificial sweeteners like sucralose, aspartame, or acesulfame potassium to improve the taste without adding calories. There is some evidence that frequent, high intake of artificial sweeteners may disrupt healthy gut bacteria and promote diarrhea for those prone to digestion issues.

Other stimulants

Ingredients like niacin (vitamin B3) and yohimbine provide added stimulation but can worsen diarrhea at the doses added to pre-workout formulas.

Who is most at risk for pre-workout diarrhea?

While anyone can experience diarrhea from pre-workout supplements, some populations are more prone to these laxative side effects:

  • Those with sensitive stomachs or digestive conditions like IBS or IBD
  • People who consume a high-fiber diet
  • Individuals taking medications that affect digestion like antibiotics
  • Older adults with slower GI motility
  • People who are new to taking pre-workout

Tips to prevent pre-workout diarrhea

Here are some strategies to help avoid diarrhea from your pre-workout:

1. Start with a lower dose

When using a pre-workout for the first time, start with less than the recommended serving size to assess tolerance. Then slowly increase the dosage over time if no diarrhea occurs.

2. Avoid taking on an empty stomach

Consuming pre-workout supplements without food can make diarrhea more likely. Have a snack containing carbohydrates and protein before taking pre-workout.

3. Stay hydrated

Drink plenty of water and electrolyte-rich fluids like coconut water before, during, and after workouts. Proper hydration promotes healthy digestion.

4. Reduce caffeine intake from other sources

Limit caffeine from coffee, tea, soda, and energy drinks when taking a caffeinated pre-workout to avoid going overboard with total intake.

5. Opt for natural sweeteners

Select pre-workouts sweetened with monk fruit or stevia over artificial sweeteners if sensitive to their laxative effects.

6. Take a probiotic

Probiotic supplements can help replenish healthy gut bacteria and reduce the likelihood of diarrhea.

7. Switch products or ingredients

Try a pre-workout with different ingredients, remove individual ingredients like caffeine or artificial sweeteners, or take an ingredient like beta-alanine separately to determine which component is causing diarrhea.

When to see a doctor

Diarrhea resulting from pre-workout is usually short-term. However, see a doctor if you experience:

  • Diarrhea lasting more than two days
  • Intense abdominal pain or cramps
  • Blood in the stool
  • Dehydration symptoms like excessive thirst, dizziness, or dark urine

These signs may indicate an underlying medical condition requiring treatment.

The bottom line

Pre-workout supplements can undoubtedly enhance exercise performance. However, ingredients like caffeine, artificial sweeteners, and beta-alanine may provoke diarrhea in susceptible individuals by irritating the digestive tract or disrupting gut bacteria.

Those with sensitive stomachs can reduce the risk of pre-workout diarrhea by starting with a lower dose, staying hydrated, consuming pre-workout with food, and avoiding large amounts of caffeine from other sources. Speak to a doctor if diarrhea becomes severe or persists longer than 48 hours after taking a pre-workout.

With some trial and error to find the right product and dosage, most people can take pre-workout supplements without digestive discomfort and reap the performance benefits.