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What ingredient in pre-workout causes diarrhea?

Pre-workout supplements have become incredibly popular among gym-goers and athletes looking to boost their energy and performance during exercise. However, some pre-workout ingredients can cause unwelcome side effects like diarrhea in sensitive individuals.

Common Pre-Workout Ingredients That May Cause Diarrhea

Here are some of the most common culprits:


Caffeine is the main energy-boosting ingredient in most pre-workout supplements. It stimulates the central nervous system and can help increase focus, alertness and endurance during a workout. However, caffeine is also a stimulant that can make some people feel jittery. It increases bowel motility, meaning it makes food move through your digestive tract more quickly. This can lead to loose stools or diarrhea, especially in doses over 200mg.

Artificial Sweeteners

Most pre-workouts contain artificial sweeteners like sucralose, aspartame or acesulfame potassium to improve the taste without adding calories. While these are considered safe by the FDA, some people find that large amounts of artificial sweeteners cause gastrointestinal distress like diarrhea and bloating.


Beta-alanine is an amino acid that reduces fatigue and builds muscle endurance. But it can cause flushing and tingling skin sensations in some individuals. High doses may also irritate the digestive tract, potentially leading to diarrhea.

Nitric Oxide Boosters

Pre-workouts often contain nitric oxide boosting ingredients like citrulline, arginine and agmatine. These compounds dilate blood vessels and enhance nutrient delivery during exercise. However, they can also relax smooth muscle in the digestive tract, resulting in loose stools in sensitive people.


Magnesium is added to some pre-workout supplements because it helps reduce muscle cramps and aids energy production. However, magnesium acts as an osmotic laxative at higher doses, drawing water into the intestines which can cause diarrhea.

Other Potential Causes of Pre-Workout Diarrhea

Besides the individual ingredients, there are a few other factors that can make someone more likely to get diarrhea from taking pre-workout:


Taking more than the recommended serving size of pre-workout can increase your risk of side effects like diarrhea. Stick to the suggested serving size to avoid overdoing the active ingredients. Start with half a serving to assess tolerance if you’re new to pre-workout.

Mixing Pre-Workouts

Stacking multiple pre-workout products together increases your overall intake of stimulants and other supplements. This spikes the risk of digestive issues. Avoid using more than one pre-workout brand or product at a time.

Inadequate Hydration

Pre-workouts drive water and nutrients into the muscles, which can leave you dehydrated if you don’t drink enough fluids. Dehydration and electrolyte imbalances can quickly lead to diarrhea. Drink plenty of water before, during and after your workout when taking pre-workout.

Individual Sensitivities

Some people may be more prone to diarrhea from pre-workout supplements due to sensitivities. This can include those with irritable bowel syndrome (IBS), food intolerances, or gastrointestinal conditions. Start with a very low dose and monitor your body’s response.

Poor Quality Products

Diarrhea can also be caused by contaminants or poor quality ingredients in some lower quality pre-workout products. Only purchase reputable brands and read labels to ensure you’re getting a high quality supplement.

Tips to Prevent Pre-Workout Diarrhea

Here are some tips to help avoid diarrhea when taking pre-workout:

– Start with a very low dose like 1/4 scoop when using a new pre-workout product for the first time. Slowly increase over time as tolerated.

– Drink plenty of water before, during and after your workout to stay hydrated.

– Avoid mixing or stacking multiple pre-workout supplements and stimulants.

– Follow dosing instructions carefully and don’t exceed the recommended serving size.

– Eat something small like a banana before taking your pre-workout.

– Let your body adjust to a new product for a week or two before increasing the dosage.

– Look for pre-workouts without proprietary blends so you can see exact amounts of each ingredient.

– Opt for pre-workouts without creatine, magnesium or vitamin B12 if you’re diarrhea-prone.

– Try lower stimulant options without caffeine or gradually reduce your caffeine intake from other sources.

When to See a Doctor

Diarrhea after taking pre-workout is usually short-lived and subsides within 24 hours as the ingredients clear your system. However, visit your doctor if you experience:

– Severe diarrhea lasting more than two days

– Bloody or black stools

– Severe pain or cramping

– Dizziness, weakness or fever

– Inability to stay hydrated

These can indicate a more serious medical condition requiring treatment. Discontinue use of the pre-workout and keep hydrated until the diarrhea resolves. See a doctor if symptoms persist.

The Best Pre-Workout Ingredients to Avoid Diarrhea

If you’re prone to diarrhea from pre-workout, choose products with more digestive-friendly ingredients like:

– Citrulline malate: Improve blood flow without gut irritation
– Beetroot extract: Boosts nitric oxide levels while soothing the stomach
– L-theanine: Provides calm energy without jitters
– Coconut water powder: Natural hydrating electrolytes that reduce diarrhea
– Betaine anhydrous: Increases strength without overstimulating the gut
– Alpha-GPC: Enhances focus through cholinergic action rather than stimulants
– L-citrulline: Vasodilator that doesn’t commonly cause diarrhea

Avoid pre-workouts with proprietary blends or high doses of caffeine, magnesium, creatine, beta-alanine or vitamin B12. Read reviews to find well-tolerated products.

The Top 5 Pre-Workouts Less Likely to Cause Diarrhea

Here are 5 top-rated pre-workouts that go easy on sensitive stomachs:

Brand Key Features
Legion Pulse – Natural flavors & sweeteners
Optimum Nutrition Gold Standard Pre-Workout – Lower 170mg caffeine
Transparent Labs Bulk – Minimal additives and dyes
Nutrex Outlift Amped – Gentler stimulant formula
Redcon1 Total War – Contains ginger and AstraGin® to ease digestion

The Bottom Line

While pre-workout can boost your performance, some ingredients may cause unwanted diarrhea in sensitive individuals if you take too much. Start low, hydrate well, and watch out for products high in caffeine, artificial sweeteners, beta-alanine, nitric oxide boosters and magnesium. Follow dosage guidelines and adjust as needed based on your personal tolerance. If problems persist, visit your doctor and switch to gentler pre-workout alternatives less prone to causing diarrhea. With some trial and error, you can find a quality pre-workout that works well with your digestive system.