Why Does Pre-Workout Make You Poop? The Real Reason

I wasn’t sure whether this was just me.

But judging by the number of times I’ve said, “Fuck, I’ve had my pre-workout — I need the toilet,” followed by the unhinged smile from my training partner who knows exactly what I mean, I’m guessing it’s fairly common.

So, I did some digging. What actually makes pre-workout send you running to the toilet?

The most likely culprit is caffeine

For most people, caffeine is the obvious place to start. It can stimulate activity in the colon and encourage the muscles in your digestive system to start moving things along.

Research has found that caffeinated coffee can produce significantly more colonic activity than water. Pre-workout isn’t coffee, but if yours contains a hefty caffeine dose, the stimulant effect may help explain why the urge appears so quickly. Research published through PubMed

If you want the wider breakdown of what is actually inside the tub, read Pre-Workout Supplements: What Do They Actually Do?

Your digestive system may already be ready to go

There’s also something called the gastrocolic reflex. When you consume food or drink, your stomach stretches and signals the colon to make room for what’s coming. That can create a sudden urge to go — especially first thing in the morning, on an empty stomach, or when you quickly neck a full shaker before training.

That “instant” trip to the toilet doesn’t mean the pre-workout has travelled straight through you. The stool was already farther down your digestive tract. The drink has simply helped trigger the contractions that move it out.

Other ingredients can contribute

Depending on the formula, caffeine might not be working alone. Magnesium can have a laxative effect at higher supplemental doses, while some sweeteners and sugar alcohols can upset the gut or draw additional water into it. The US National Institutes of Health notes that high supplemental magnesium intakes can cause diarrhoea, nausea and abdominal cramping. NIH Office of Dietary Supplements

Taking a concentrated mixture quickly and on an empty stomach may make the effect more noticeable. Beta-alanine — the ingredient responsible for that familiar tingling sensation — normally isn’t the main reason you need the toilet.

Is it normal?

A mild urge to go shortly after taking pre-workout is fairly common, particularly if you’re sensitive to caffeine. It doesn’t automatically mean anything is wrong with you.

Regular diarrhoea, painful cramps, vomiting or severe urgency is different. That can suggest the product, serving size or caffeine dose doesn’t agree with you. Check the label rather than assuming every pre-workout formula is the same.

It’s also worth looking at the rest of your intake. If your stomach is already struggling with large shakes or a sudden increase in protein, The Complete Guide to Protein Powder explains what else may be contributing.

Is it flushing old food and bloating out of your body?

No. It might feel as though the pre-workout is “clearing you out,” but it isn’t detoxing your body or suddenly forcing old food all the way through your digestive system.

Going to the toilet may temporarily leave you feeling lighter or less bloated, but that isn’t the same as cleansing the body. Your liver, kidneys and digestive system already handle waste without needing a pre-workout detox.

What can you do about it?

If it happens every time, try half a serving, drink it more slowly, take it with a small amount of food, or compare it with a stimulant-free formula. Don’t double-scoop a strong product just because you’ve become used to the feeling.

And perhaps leave yourself an extra ten minutes before setting off for the gym.

Because nothing ruins a heavy squat session quite like realising your pre-workout has kicked in from both directions.

This article is for general information and isn’t medical advice. Speak to a healthcare professional if bowel changes are persistent, severe or accompanied by blood, unexplained weight loss or significant pain.