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Why Does Pre-Workout Make You Poop? (Expert's Opinion) 

Tyler Sellers
Published by Tyler Sellers | Senior Coach
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: April 23, 2023
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That's a serious question a few of my clients have asked me about the pre-workout supplement they were taking.

While abnormal bowel movements are not something I've encountered with pre-workouts, I decided to check with a nutritionist about why some people might end up with some stomach issues.

It turns out that there are some common pre-workout ingredients that occasionally cause stomach issues. So, we did some deeper research for a few weeks to see if we could figure out what causes it and whether there are ways to avoid it.

So, why does pre-workout make you poop? Let's take a look.

Quick Summary

  • Pre-workout supplements can make you poop because of the combination of the ingredients, and also depending on how you are using it.
  • The ingredients that might affect your stomach are caffeine, artificial sweeteners, magnesium, and lactose.
  • Some tips for reducing pre-workout poops include reducing caffeine intake, switch pre-workouts if one isn't working for you, and also taking the right dose.

Why Does Pre-Workout Make Me Poop?

A man sitting on the toilet

A pre-workout supplement makes you poop a lot, most likely because of a combination of the ingredients and the way you use it.

In most cases, this is down to the effects of caffeine or artificial sweeteners.

Now, caffeine is an important and effective ingredient for pre-workout, as it can improve strength and delay muscle fatigue [1].

At the same time, caffeine has been linked to increased bowel movements [2].

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The problem is that some supplement companies take an extreme approach to stimulants.

And with a very high dose of caffeine and possibly having a cup of coffee not long before taking the pre-workout, it can have an intense effect on your stomach.

The other ingredient that can cause stomach issues and even diarrhea is some form of artificial sweetener [3].

The other thing that can contribute to bowel trouble is how much and when you take your pre-workout.

More on these shortly.

Pre-Workout Ingredients That Might Affect Your Stomach

A man holding a toilet paper roll while sitting on the toilet

I gathered the name of each pre-workout supplement that my clients had reported issues with and then had my nutritionist review them to see what the most likely cause was.


Most pre-workout supplements contain some amount of caffeine, and that is because it can help you achieve a more intense workout session [4].

As we’ve mentioned, caffeine has been liked to increased bowel movements, but the main reason this might cause issues more often than it actually should is a high dose in these supplements, which can even lead to diarrhea [5].

The products that I recommend generally have less than 200 mg of caffeine, and that's about the same as two cups of coffee. And while up to 400 mg is classed as safe per day, you don't want to get that all in one go [6].

In the end, if you are sensitive to it, caffeine-free pre-workouts are the best option for you.

Artificial Sweeteners

Sugar inside a wooden bowl

Artificial sweeteners are common in all supplements, not just pre-workouts. And studies have shown that they can destabilize your gut flora, leading to many different bowel issues [7].

And what then happens is that undigested sweetener absorbs water, which leads to softer stool.

One problem, in particular, is diarrhea, and it's often linked to a regular and consistent intake of artificial sweeteners.

And considering that you might be taking a pre-workout four or five times a week, that's one area where you need to pay close attention.


Lactose is less common in these products, but one of my clients used a pre-workout supplement that had lactose, and it was causing him many stomach issues.

If you have any kind of lactose intolerance, then it can make you poop a lot more and often at very inconvenient times [8].


Magnesium is an important mineral for muscle mass and a healthy lifestyle in general [9]. But some forms of this mineral can trigger digestive discomfort in the form of cramps, bloating, and diarrhea [10].

If you see a high dose of magnesium in a pre-workout and you take it in some other form as well, then you could end up with stomach issues.

"​​Magnesium supplements can cause nausea, cramps, and diarrhea. Magnesium supplements often cause softening of stool."

- R. Morgan Griffin, Writer & Editor at

Other Contributing Factors

A man sitting on the toilet

Beyond the ingredients in your chosen pre-workout supplements, there are a couple of other things that can impact a timely bowel movement.


Here are two things to consider for timing.

When you take pre-workouts with caffeine content around the same time as a cup of caffeinated coffee, then you can quickly end up with a very large dose of caffeine.

Also, if you take it at the same time as other supplements with similar ingredients, it can further cause bowel issues.

Try to avoid that cup of coffee and avoid other supplements at the same time, and you might find that this problem is gone.

Related Article: Pre-Workout vs Coffee


The first thing you should do is check the labels of pre-workout supplements and see how much caffeine is in them.

Some of them have very high doses, and if you drink caffeinated coffee as well, then it can impact your bowels, brain and nervous system, as well as blood pressure [11].

Empty Stomach

If you take pre-workouts on an empty stomach before fasted cardiovascular exercises and it contains artificial sweeteners and magnesium, then it significantly increases your chances of not having a normal or proper bowel movement.

I have a few tips for dealing with these situations, and you should definitely try them out if you've had issues.

Tips For Reducing Pre-Workout Poops

A stack of toilet paper rolls while someone in the background is sitting on the toilet

If you find that pre-workout makes you poop a lot more than you did before, then here are a few tips to deal with it.

Switch Pre-Workout

The first thing you want to do is check the pre-workout for high doses of caffeine and artificial ingredients. If the label looks like it was taken from a chemistry set, then it's a possible cause of bowel issues.

We have tested out dozens of pre-workouts over the years, and there are a few with low or no caffeine pre-workouts that should stop bowel problems while still improving your energy levels.

Reduce Coffee Intake

If you prefer a pre-workout with caffeine, then I would suggest that you reduce how much coffee you drink. You should do this, especially leading up to an exercise session where you simply can't afford to have an upset stomach.

Check Overlapping Ingredients

A man pointing at a pill bottle

Another common cause for pre-workout poops is overlapping ingredients between multiple supplements.

If you take a fat burner and some mineral supplements to support high-intensity exercises, then it can quickly happen that you get too much of a mineral like magnesium.

If you see a lot of similar ingredients, then you should adjust your timing so that you don't end up taking them within a few hours of each other.


Does Pre-workout Make Your Stomach Hurt?

Yes, some pre-workout products can make your stomach hurt. But there are supplements that have a more stomach-friendly formula to help you avoid cramps and bloating.

How Do You Stop Pre-workout Diarrhea?

You can stop pre-workout diarrhea by making sure you don't take a product with too much caffeine and artificial sweeteners. You should also try to take it with some food to avoid stomach upset.

Take Action To Avoid Pre-Workout Bowel Issues

At this stage, you should understand what to do if you've had the unpleasant experience of a sick stomach and bowel movement problems from pre-workouts.

The most likely reason is a combination of very high caffeine and artificial ingredients that are known to cause stomach problems. And the best thing you can do in this case is switch to a different supplement.

We've created a list of the best men's pre-workouts after testing and researching dozens over the years. These have given us great results during training sessions, and they haven’t caused any significant bowel problems so far.

Make sure to check them out if you want to avoid these unpleasant side effects.


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