Is it normal for pre-workout to give you diarrhea?

Pre-workout supplements have become increasingly popular among gym-goers and athletes looking to boost their energy and performance during workouts. However, some pre-workout ingredients may cause side effects like diarrhea in certain individuals.

What’s in Pre-Workout?

Pre-workout supplements typically contain a blend of ingredients like:

  • Caffeine – Provides energy and enhances focus
  • Beta-alanine – Reduces fatigue and increases training capacity
  • Creatine – Improves high-intensity exercise performance
  • Nitrates – Boosts blood flow and oxygen delivery to the muscles
  • Amino acids – Helps reduce muscle damage and aids recovery

The specific combination and doses of ingredients can vary widely between different pre-workout products. Some lesser known compounds like geranamine or dendrobium may also be added to the proprietary blends.

Pre-Workout Ingredients That May Cause Diarrhea

Certain ingredients commonly found in pre-workout formulas can irritate the digestive tract in some individuals, potentially leading to side effects like diarrhea, cramps, and bloating. The main offenders include:


Caffeine is perhaps the most common pre-workout ingredient linked to diarrhea. Typical pre-workouts contain 150-350mg of caffeine per serving, often in the form of caffeine anhydrous.

Caffeine acts as a stimulant that can increase bowel movements and loosen stools. Too much caffeine at once may overwhelm the digestive system and cause diarrhea in predisposed individuals.


Magnesium is added to some pre-workouts due to its role in energy production and muscle function. But it’s also known to have a laxative effect at higher doses.

Forms like magnesium citrate are commonly used as colon cleansers to induce bowel movements. While pre-workouts don’t contain nearly as much magnesium, it could still trigger diarrhea in sensitive persons when combined with other stimulants.


Beta-alanine can cause a tingling, prickly sensation called paresthesia when taken in doses over 800mg. Some research also indicates it may provoke diarrhea and stomach pain in excess amounts.

The diuretic effects of beta-alanine could partly explain its potential laxative properties when consumed in a pre-workout supplement.

Artificial Sweeteners

Most pre-workouts contain artificial sweeteners like sucralose or acesulfame potassium to improve the taste without adding sugar. Certain sweeteners are known to have laxative effects in large amounts.

For example, the FDA sets the acceptable daily intake limit for sucralose at 5mg per kg of body weight. Going well over this limit via pre-workout can upset your stomach.

Other Potential Causes

Aside from specific ingredients, there are other factors that make some people more likely to get diarrhea from taking pre-workout:

  • Dose – Taking too much pre-workout can overload the body with stimulants and upset your stomach.
  • Sensitivity – Having a preexisting condition like IBS or food intolerances may increase diarrhea risk.
  • Dehydration – Not drinking enough water when taking stimulant-based supplements may worsen side effects.
  • Improper Diet – Caffeine on an empty stomach or before a workout can further disrupt digestion.

Ways to Prevent Pre-Workout Diarrhea

You can try these tips to help avoid diarrhea when taking pre-workout:

Reduce the Dose

Only take about half the recommended serving size to assess your tolerance, then slowly increase the dose if needed.

Spread Out Intake

Split your regular dose into two smaller servings taken 30-60 minutes apart to minimize stimulant impact.

Stay Hydrated

Drink plenty of fluids before, during, and after your workout to counteract dehydration from stimulant effects.

Eat Something

Never take pre-workout on an empty stomach – always have a light snack beforehand to help absorption.

Avoid Certain Ingredients

Opt for stimulant-free pre-workouts or those without known laxatives like magnesium if you’re sensitive.

Allow Time to Adjust

Diarrhea side effects may subside after a week or two as your body gets used to the supplement.

How Long Does Pre-Workout Diarrhea Last?

For most healthy individuals, diarrhea caused by pre-workout should be mild and temporary, lasting:

  • 30 minutes to 2 hours when caused by caffeine
  • 2 to 12 hours when caused by artificial sweeteners
  • Less than 24 hours when caused by other ingredients

However, effects may persist longer or recur with repeated use in sensitive persons. Stop taking the supplement and see a doctor if diarrhea lasts over two days.

When to See a Doctor

Consult a physician promptly if you experience:

  • Diarrhea lasting over 48 hours
  • Fever or vomiting along with diarrhea
  • Signs of dehydration like dizziness, excessive thirst, or dark urine
  • Bloody or black stools
  • Severe abdominal pain or cramping
  • Inability to keep any food or liquids down

These may indicate a more serious condition requiring medical treatment. Seek emergency care if diarrhea is accompanied by symptoms like weakness, rapid heart rate, or confusion.

Tips for Reducing Pre-Workout Side Effects

Here are some general recommendations to help minimize adverse effects from pre-workout supplements:

Take With Food

Tip Explanation
Take with food Ingest pre-workout with a light meal or snack to avoid stimulants on an empty stomach
Stay hydrated Drink plenty of non-caffeinated fluids before, during, and after workouts
Follow dosing Don’t exceed recommended serving sizes or dosing instructions
Allow breaks Cycle on and off pre-workout supplements to avoid building tolerance

Taking pre-workout with some food helps slow absorption and reduces side effects compared to ingesting it while fasted. Aim for a combination of carbs and protein.

Stay Hydrated

Drinking adequate water counteracts the dehydrating effects of stimulants in pre-workout. Shoot for 12-16 ounces before, during, and after your workout when using supplements.

Follow Dosing Instructions

Never exceed the recommended serving size or dosing guidelines on the label. More isn’t necessarily better with pre-workout due to high stimulant amounts.

Allow Off Cycles

Take a break from pre-workout every 4-8 weeks to prevent building up a tolerance to the ingredients. Cycling helps maximize the benefits when resuming use.

Risks of Pre-Workout Overuse

While pre-workout can improve exercise performance when used properly, overdoing it can be harmful. Potential risks include:

  • Dependence – You may develop a psychological or physical reliance on supplements to get through workouts.
  • Tolerance – Larger doses may be needed over time to feel the same effects.
  • Side Effects – Headache, jitters, nausea, and heart palpitations may occur with excessive intake.
  • Dangerous Interactions – Adverse reactions with medications or preexisting conditions.
  • Overdose – Extremely high doses of stimulants can potentially be life-threatening.

Using pre-workout as a crutch to compensate for poor sleep, nutrition, or training can ultimately do more harm than good. The benefits start to diminish if you become reliant on supplements.


It’s fairly common to experience some diarrhea or loose stools when first starting to use pre-workout supplements. This is typically due to high amounts of stimulants like caffeine that can disrupt normal digestion.

Side effects normally improve within a few weeks as your body adapts. But using smaller servings, staying hydrated, and taking precautions can minimize diarrhea risk.

See a doctor if you have persistent or severe diarrhea, as it could indicate an underlying health condition or reaction to certain ingredients. When used properly alongside a balanced diet and training program, pre-workout can be taken safely without significant gastrointestinal effects for most individuals.

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