Pre-workout Side Effects: Is It Worth Taking?

Craig Primack, MD, FACP, FAAP, FOMA

Reviewed by Craig Primack, MD, FACP, FAAP, FOMA

Written by Rachel Sacks

Published 04/29/2024

If you work out, you’ve probably heard about the slew of  dietary supplements designed to boost energy levels, increase athletic performance, aid exercise recovery and maximize your every workout..

Generally referred to as pre-workout supplements, they often come in powders, premixed drinks, pills or snack bars — making them fairly easy to use.

But while these supplements can provide benefits, you’ll want to watch out for side effects like digestive issues, water retention and headaches.

Below, we explore the common side effects of pre-workout, explain how to avoid them and answer frequently asked pre-workout Qs.

The five most common side effects of pre-workout include:

  • Feeling jittery

  • Increased water retention

  • Digestion issues

  • Headaches

  • Mild reactions

Before we dive into more detail, we want to make this clear: There are benefits of pre-workout and it’s generally considered safe to use — although many studies only looked at the effects over eight weeks. You should also know that the Food and Drug Administration (FDA) doesn’t test dietary supplements.

Feeling Jittery

What does pre-workout feel like? Well, you might have increased energy, or feel extra wired or excited.

If you feel like you drank one too many cups of coffee after taking pre-workout, that’s because caffeine is often a primary ingredient.

While feeling jittery may be a common pre-workout side effect, the effects of caffeine have been shown to increase muscle strength and output during exercise.

Caffeine may also affect how well you recover after workouts as well as your heart rate variability, the difference in the amount of time between heartbeats.

Nonetheless, consuming too much caffeine has several potential side effects — including insomnia, nausea, increased heart rate, headaches, anxiety and restlessness.

So if you were wondering, does pre-workout have caffeine? The answer is typically yes, though the amount of caffeine varies. Some pre-workout supplements can contain up to 300 mg of caffeine while others have far less.

Even though caffeine affects everyone differently, research suggests that caffeine consumption from pre-workout tends to be well-tolerated.

Increased Water Retention

Another common pre-workout ingredient, creatine, may be responsible for this side effect: extra fluid trapped in your body, also known as water retention.

Whether taken as part of a pre-workout supplement or on its own, creatine has been shown to increase lean body mass gains from exercise.

While less researched, creatine is also associated with weight gain over time, which may be a result of water retention.

So does pre-workout have creatine? Yes, but the long-term effects of pre-workout on water retention are not as clear.

Digestion Issues

Several ingredients in pre-workout formulas — like sodium bicarbonate, magnesium and caffeine — may cause digestive issues.

Magnesium may have laxative effects and taking too much may cause diarrhea.

Meanwhile, sodium bicarbonate may cause problems if you consume more than 0.3 g per kilogram of body weight. The good news? Most pre-workout supplements don’t contain this much.


Another side effect of pre-workout may be headaches, thanks to an amino acid called citrulline.

Found naturally in watermelon or taken as an L-citrulline supplement, citrulline boosts nitric oxide levels in your blood.

This increases blood flow to your muscles, increasing muscle mass and improving endurance exercise.

Since this increase in blood flow affects your brain as well as your muscles, citrulline could cause some people to experience headaches and migraine due to blood pressure changes in the blood vessels in your brain.

Mild Reactions

Two other common ingredients in pre-workout — beta-alanine and niacin (vitamin B3) — may result in mild reactions.

Beta-alanine has been shown to increase exercise performance and reduce fatigue in high-intensity exercises lasting one to four minutes.

But while beta-alanine is generally safe and well-tolerated by most people, some may experience a nervous system reaction that results in a tingling sensation.

And while niacin may help with energy metabolism, high doses of 500 mg or more can trigger skin flushing.

Now that you know the pros and cons of pre-workout, you probably want to know how to get rid of pre-workout side effects.

One easy approach? Reduce the amount of pre-workout you take, thereby reducing the dosage of some ingredients.

Everyone reacts differently to different dosages of common pre-workout ingredients, such as the amount of caffeine they consume. Starting with a small dosage of pre-workout and then gradually increasing your dosage will help you see what you can tolerate.

Trying different pre-workout formulas is another way to determine which ingredients cause side effects for you.

You can also check the ingredients before buying pre-workout to avoid the ones that tend to cause side effects, like niacin.

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What else should you know about pre-workout? We dig deeper below.

Is Pre-Workout Safe?

If you can experience side effects from pre-workout, is pre-workout bad for you?

The International Society of Sports Nutrition (ISSN) states that pre-workout is an effective nutritional supplement for gaining lean body mass and increasing exercise performance, especially in high-intensity activities.

But since pre-workout isn’t tested by the FDA, you might want to consult with a healthcare provider before adding a new one to your routine.

Can You Take Pre-Workout Every Day?

Since the amount of ingredients in many pre-workout supplements is on the lower side, you can use it every day. However, you probably shouldn’t take pre-workout more than once a day.

While pre-workout can give you a boost on days you’re feeling sluggish, you’ll want to keep an eye on any side effects you experience, like feeling jittery from the extra caffeine.

Follow the dosage instructions and try lowering the dose or consider switching pre-workouts if you notice any side effects from taking supplements every day.

What Does Pre-Workout Do to Your Body?

So it’s generally considered safe to use, but is pre-workout good for you?

You’ll still benefit from exercise even if you don’t use pre-workout, but it may help increase your exercise performance after training for six months.

Can pre-workout make you sick? This can depend on how you react to certain ingredients and how much pre-workout you take. Some people may notice more pre-workout side effects than others.

Does Pre-Workout Make You Gain Weight?

Possibly. One known side effect of creatine — a common pre-workout ingredient — is weight gain, thanks to its effects on water retention.

However, some studies suggest that creatine in pre-workout may not cause weight gain.

More research is needed to make a definitive call.

If you exercise regularly, you might consider using pre-workout supplements. But knowing that pre-workout can cause side effects, are they worth taking? Let’s break it down…

  • A popular addition to fitness routines, pre-workout products typically contain a variety of ingredients such as caffeine, creatine, beta-alanine and L-citrulline.

  • Individual ingredients can cause side effects like jitters, water retention, headaches, digestion issues and mild reactions.

  • Many of the individual ingredients in pre-workout supplements are shown to improve exercise performance, but there’s limited evidence on the effectiveness of pre-workouts that contain multiple ingredients.

While pre-workout is generally safe and tolerated by many, you can check the ingredients list and adjust how much you take if you’re concerned about side effects.

If you’re trying to lose weight and specifically concerned about weight gain as a potential side effect of pre-workout, talk to a healthcare professional about weight loss medications as well as what type of pre-workout they may recommend.

It’s important to remember that while pre-workout can be helpful, successful weight management plans include a balanced diet, regular exercise, plenty of sleep and more.

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