7 Pre Workout Side Effects You Should Be Aware Of

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Woman in background drinking her pre workout supplement, from the article Pre Workout Side Effects on heydayDo

Certain pre-workout supplements provide performance-enhancing benefits no doubt, but some give us unwanted side effects too.

This article looks at the most common side effects of taking pre-workout supplements and the individual ingredients that cause them.

And I also share what medical & nutrition experts offer as solutions towards avoiding each one of those seven side effects.


7 common side effects from taking pre-workout supplements

Nervousness / Agitation 

Problems sleeping

Increased blood pressure



Prickly heat + itching on skin


Specific ingredients in pre-workout formulations are responsible for specific side effects, so knowing who’s causing what goes a long way towards avoiding anything harmful.

Pre-workout supplements affect each of us differently; we don’t all feel them to the same degree.

This isn’t surprising since:

1) there’s a lot of body weight variation among the workout faithful, and 300 mg of caffeine to a 350 lb. dude may not act the same as it would to a 100 lb. person;

2) we’re all genetically wired differently, so chemicals affect each of us differently.


What’s next

In the sections up ahead we’ll look at each of the common side effects caused by pre-workout supplements and I’ll discuss the specific ingredient(s) responsible for causing each unwanted effect.

I’ll also offer suggestions on how to either minimize that unwanted effect or avoid it entirely, and answer a couple of the frequently asked questions about pre-workout formulas as well.


test tubes green - heydayDo icon

Science resources included

As is my custom here on heydayDo, I will provide links to all of the relevant sports science & medical resources, clinical studies, and nutritional data used in this article.


Pre-workout supplements – side effects & ingredients

Although there are countless pre-workout products on the market, most pre-workout supplements are formulated around the same handful of potent ingredients.

And given the strong dosages often used in pre-workout products, it’s not much of a surprise to learn that some unwanted side effects come along with the intended beneficial effects.


Sports science knows pre-workout supplements very well

The most popular individual ingredients in the majority of supplement formulas made for pre- or post-workout have been extensively studied by sports science researchers for the performance boost they can provide.

Athletic performance — speed, strength, explosive power, etc. — can be measured, and most pre-workout supplements have a number of strength & conditioning studies focused on figuring out how effective they are.


After all, that’s why (not too long ago) someone decided to start combining these individual supplements into a single product and marketing it for pre- & post-workout, intra-workout/workout fuel, etc.


And so along with the known athletic performance-enhancing effects of each individual supplement, sports science researchers came to be familiar with any of the unwanted side effects that some people dealt with too.


Easy to determine the guilty party

That’s why it’s pretty easy to pin a pre-workout side effect on a specific ingredient that’s contained in that product.

That same handful of common side effects I listed above happen the most since there’s the same handful of essential performance-enhancers in every popular pre-workout, along with similar added sweeteners, etc.


Every person is affected differently

For several reasons, there is a broad range of reactions to the main ingredients in many pre-workout supplements. We’re all:

  • in different physical condition;
  • in different mental health condition;
  • on different fitness levels;
  • eating different diets;
  • on different schedules;
  • and so on.


So the bottom line is …

How much our body has a particular side effect from the same ingredient can vary widely from person to person: from little or no effect at all to having severe symptoms.

It depends on us, what dietary supplements we’re taking, when we’re taking it, & how much we’re taking.


Side effects & their responsible ingredients

Woman dressed as demented clown, a metaphor for bad pre workout supplement side effects - heydayDo image

OK, let’s see which ingredients out of the many pre-workout supplements out there are known to cause unwanted side effects.

Where appropriate, I’ll also provide a plan of action on how to minimize or avoid that side effect if you find that that particular ingredient is a problem.


1. Nervousness / Agitation

Main ingredient responsible: Caffeine

This is one of the more common side effects of pre-workout supplements.

When a manufacturer in the supplement industry tells you that their product will provide you with “energy, motivation, & focus” (that you’re lacking apparently, didn’t you know 😄), what they mean is they’ve put a bunch of caffeine in it.

Caffeine does indeed provide a number of performance-enhancing benefits, sports science has proven that (1).

Caffeine’s demonstrated many times over that it can increase workout strength & power, which will help with muscle growth goals for sure. (34)

But in high doses, it can start to affect you in a not-as-productive way, specifically as it comes to feelings of nervousness, agitation, and/or increased anxiety.


Our caffeine sensitivity levels

We’re all different and have different sensitivity levels to caffeine (2).

But the Mayo Clinic notes that generally, side effects from too much caffeine can start to kick in once you’re above 400mg (3).

Over 40 million Americans have some sort of anxiety-related mental health issue (4).

People with an underlying nervous condition, low-grade anxiety, elevated cortisol or stress levels, etc., are more at risk for worsening their conditions via caffeine (5).

This increased sensitivity to caffeine means that they’re more likely to experience increased nervousness & anxiety after taking a pre-workout formula.


Caffeine supplement + other dietary caffeine sources

Caffeine effects can affect you for several hours: it takes 5-6 just for half of the caffeine to wear off (6).

So if you’ve had other types of caffeine prior to or after you drank your pre-workout supplement, your total level of caffeine for that time frame might put you in the red.


How to avoid this side effect:

*Know how much caffeine is in your pre-workout powder, and know your caffeine sensitivity level.

*Avoid going over the amount of caffeine your body can handle symptom-free.

*Avoid caffeine for several hours before & after you take your pre-workout.

*If you have a preexisting nervous or stress condition, caffeine’s a poor supplement choice; you may want to consider avoiding any pre-workout supps with caffeine.


Bottom Line: Given that many pre-workout formulas have a lot of caffeine in them and that a lot of Americans have some level of anxiety, it’s unsurprising that nervousness & heightened anxiety are often considered the most common of pre-workout side effects. 


2. Problems sleeping

Main ingredient responsible: Caffeine

No surprise here.

Caffeine is a powerful stimulant and that’s why medical experts always consider it one of the main culprits when someone has problems with their sleep patterns (7).

As I mentioned earlier, research shows that caffeine can stay in your system for quite awhile, and can disrupt your ability to sleep even if you’ve gone several hours since taking some (8).

Safe to say that a night time training session probably shouldn’t be preceded by downing a caffeinated beverage.

And even if you work out in the late afternoon and take a pre-workout supplement, your sleep could become affected.

Young woman handing over a cup of coffee to me pre-workout

Caffeine >> stress >> insomnia

In addition to that, remember we noted earlier that caffeine can increase the stress level in some people.

It’s been proven to raise cortisol levels, which is the body’s reaction to stress (9).

And stress is also one of the main reasons people develop insomnia (10).


Cycle of poor sleep > more caffeine > more poor sleep

If your sleep pattern is fouled up, you’ll obviously wake up the next day unrefreshed and probably tired. This can lead some people to taking more pre-workout in order to get the boost in energy/motivation/focus that they’ve lost since they’re not getting the quality of sleep their bodies need.

This is a negative cycle that can lead to poorer sleep and eventually other health problems, including high stress levels and decreasing physical performance.


How to avoid this pre-workout side effect:

*Avoid taking pre-workout at least 8 hours prior to bedtime.

*If you’re experiencing stress or anxiety, caffeine will likely make your condition worse, so simply avoid caffeinated pre-workout supplements.

3. Increased blood pressure

Main ingredient responsible: Caffeine

Caffeine is at it again; another of its side effects is temporary hypertension. Medical studies have shown that caffeine can cause sharp increases to your blood pressure for the short-term after taking it (11).


Majority of adults have higher than normal BP

And believe it or not there are more American adults with either high BP or pre-hypertension (borderline high) than there are healthy adults, according to the American Heart Assn. (12).

Given those numbers, it’s no shock that a common side effect of taking pre-workout is experiencing a spike in blood pressure.

This temporary condition can result in the following symptoms (13):

  • shortness of breath
  • headaches
  • blurred vision
  • chest pain

People with high blood pressure issues can expect to see their BP numbers rise after taking a caffeine supplement, since drinking lots of caffeine has been shown to affect that segment of the population that way (14).

And caffeine has been shown to increase the BP in normal populations too, so no one is spared at least a little of this side effect (15).

But if you’re in good health you may not experience any of those symptoms, or only feel them very slightly.


How to avoid this side effect:

*Avoid caffeinated supplements if you’ve been diagnosed with high blood pressure or pre-hypertension.


4. Headaches

Main ingredients responsible: Citrulline & Caffeine 

L-citrulline is classified as a non-essential amino acid, but has shown itself to be pretty essential to many a strength trainer, yours truly included.

That’s why it is included in many fitness supplement formulas in the market these days.

L-citrulline with malate increases nitric oxide in us which can expand your blood vessels & boost the flow of blood into your tissues, and all us muscle builders love that pump (16).


I take citrulline malate on its own — not in a formula — to reduce the typical soreness called DOMS I get in my muscles a day or two after working out them out.

DOMS = delayed onset muscle soreness, and citrulline’s good for that (17).

Unfortunately for some people, as citrulline opens your blood vessels and increases blood flow to your brain via nitric oxide, headaches can occur (18).


Caffeine causes headaches too, for some

Woman with headache side effect from her pre workout supplement leans on her treadmill

You might be aware that caffeine is used in pain-reliever formulas to treat headaches when it’s paired with acetaminophen or aspirin.

So you might be wondering “How can it both relieve headaches and cause headaches?”, a reasonable question no doubt.


Remember back in the article where caffeine was guilty of temporarily causing high blood pressure?

And one of the symptoms of high BP is headaches.

And also, remember where I showed how caffeine can increase cortisol levels and induce stress symptoms?

Well, stress itself has been medically demonstrated to cause headaches too (19).


How to avoid this side effect:

(I’m sounding like a broken record I think…)

*Avoid caffeinated supplements if you’ve got high blood pressure, high cortisol levels, or a mental health issue like anxiety, etc.

*Avoid citrulline as an ingredient once you’ve determined it’s causing the headache.

I emphasize that point because for healthy individuals, a headache caused by pre-workout formulas could just as easily be caused by a mega-caffeine dose.


Another reason it might not be the citrulline is that some pre-workout supplements only put a skimpy amount of L-citrulline or citrulline malate in them.

In other words, not enough to do you any harm or any good.


5. Diarrhea

Main ingredients responsible: Magnesium, Sugar Alcohols

There aren’t any clinical research studies dedicated to inducing diarrhea with pre- or post-workout drinks.

I suppose that’s a good thing, especially for researchers & their participants. 😄


No sports research evidence means I don’t have my usual arsenal of scientific proof of why this causes that, which is my normal way of getting to the truth in the world of health & fitness.

But I did get some helpful info from someone whose opinion on supplements I trust, and that’s Consumer Labs (20).

They wrote up an article on supplements that can cause diarrhea, and a few things caught my eye.



Magnesium is sometimes used in pre-workout supplements, but it wasn’t listed on the majority of ingredients labels I scanned recently. But keep an eye out for it, because magnesium is used as a laxative in over-the-counter medications.

And that fact alone pretty much implicates it in any pre-workout diarrhea fiasco you might find yourself embroiled in. But that’s if it’s one of the ingredients.


Sugar alcohols

Another suspect is the synthetic — though classified as natural — ingredient known as sugar alcohols that’s often piled into a pre-workout.

Medical experts at Mayo have linked sugar alcohols to stomach upset, gas, and diarrhea (21), and Penn State University Medical Center in Hershey also has as well (22).

A lot of pre-workout supplements, drinks, & powders have plenty of sugar alcohols or artificial sweeteners in them, in an unfortunately unsuccessful attempt to mask their gnarly taste.

Most of the. names of sugar alcohols rhyme, so look for anything ending in -ol:

  • erythritol
  • lactitol
  • maltitol
  • mannitol
  • sorbitol
  • xylitol
  • isomalt

source: U.S. Food & Drug Administration (FDA)


Any sugar substitute is a diarrhea suspect

Harvard Medical says that diarrhea that’s not caused by a viral condition is likely food-borne and their list includes all artificial sweeteners (24).

They classify them as “poorly digested sugars” that our bodies have difficulty dealing with.

In other words, they’re foreign to our bodies and so they’re treated as invaders who must be vanquished.

Or in our case of diarrhea, flushed out of our system.


How to avoid this pre-workout side effect:

*If your workout formula is giving you the runs, try & determine which ingredient is the source of your diarrhea.

If it doesn’t have magnesium or magnesium citrate in it, check how it’s sweetened.

*It’s tough (impossible?) to find a powdered fitness supplement meant to be mixed with water that is not artificially sweetened.

Nobody seriously into strength training & nutrition wants high sugar content or empty carbs in their life, let alone in their workout supplements.

So you may have to switch brands until you find one whose sweetener isn’t giving you the digestive blues.


6. Prickly heat /itchy skin /tingles

Main ingredients responsible: Beta-alanine, Niacin

If you’ve ever popped a stout B-complex vitamin with loads of niacin in it, then you’re familiar with some or all of the sensations associated with the niacin flush:

  • tingly or prickly sensation;
  • blood flushing to your face;
  • tingling;
  • itchy or lightly burning skin.

Niacin is included in some workout formulas because it improves blood flow to muscle tissue (25).

Beta-alanine, found in most pre-workouts, is a non-essential amino acid that’s been proven to provide performance-enhancing benefits for a range of athletic training activities (26).

It too causes tingling sensations similar to the niacin flush.

These feelings are a little bothersome for some people, but they do go away after an hour or two at the most.

And there’s no lingering health issue associated with those side effects: that’s just the feeling of your blood on the move.


How to avoid this side effect:

*I think it’ll be hard for you to find a “beta-alanine free” product that’s made for taking before you workout.

I think every product I looked at recently had beta-alanine in it, which isn’t real surprising since it’s proven to be an effective workout enhancing supplement.

But I think the side effects are definitely stronger in any workout formula that has some niacin in the recipe on top of the beta-alanine.

And since niacin’s not in every workout supplement out there, you could switch to a niacin-free blend if you’re finding that flush effect too much to deal with.


*There are ways to reduce the feeling of the niacin flush, but I don’t think they’re good for someone who’s taking a pre-workout before going and busting out a good workout.

Besides, those methods aren’t proven to work with beta-alanine’s flush sensations, so why bother?

Anyway, the two common approaches to reducing a niacin flush is to eat something with it (something that is not totally in line with taking a pre-workout supplement), or popping some aspirin 30-60 minutes prior to downing the niacin.

7. Dehydration

Main ingredients responsible: It might be YOU

Here’s a scenario that gets reported on weightlifting forums every so often:

  • Person takes pre-workout.
  • Person hits gym.
  • Person during workout or afterwards says they feel dehydrated.
  • Pre-workout supplement takes the blame.

So we see that the person’s perception of being dehydrated is blamed on ingredients contained in the pre-workout supplement.

And the two big mainstays of most pre-workout formulas, caffeine & creatine, are usually the ones who get blamed… though I’m not so sure that’s a correct assumption.

Dehydrated young woman crawling on desert sand reaching for a bottle of water just out of reach

Taking a pre-workout supplement? Drink a lot of water, or else.


Caffeine does not cause dehydration

Medical research has shown that caffeine is not a diuretic.

You may pee a lot, but you don’t get rid of any more than you drank in the first place (27).

The Mayo Clinic simply says

“While caffeinated drinks…may cause the need to urinate — they don’t appear to increase the risk of dehydration.”


Creatine does not cause dehydration

I was reading somewhere in the ISSN (International Society of Sports Nutrition) Journal last night where they said that creatine is one of the most researched sports supplements ever, and I believe them.

I’ve seen boatloads of creatine research in the National Institute of Health’s research library (28).

And a handful of creatine studies have been directed at whether creatine causes dehydration.

Representative of all those results is this study from the Human Performance Lab at Ball State University.

It showed no signs of dehydration whatsoever among the research study’s exercising participants (29).

And in another creatine study, creatine actually reduced one of the main symptoms of dehydration – cramping – by almost 60% compared to the control group who wasn’t given any creatine (30).


No common ingredients used in pre-workout formulas dehydrate you

There is no scientific or medical evidence that I could find that links dehydration to any of the usual pre-workout ingredients:

  • caffeine
  • creatine
  • citrulline
  • beta-alanine
  • betaine
  • theanine


Dehydrated…or under-watered?

If none of the most common ingredients used in pre-workout supplements cause dehydration, why were those people saying they felt that way?

I’ll never know for sure, but maybe those people weren’t hydrating themselves enough.

Maybe they weren’t aware that they need to drink more water than normal every day while taking pre-workout supplements like creatine & citrulline.


How to avoid this side effect:

A glass of water from How Much Water Should I Drink with Creatine article on heydayDo


Here are answers to a few of the common pre-workout side effects questions people ask.


How long do pre workout effects last?

It depends on the symptom.

The diarrhea caused by either the sugar alcohols/artificial sweetener or any magnesium in the pre-workout shouldn’t last more than a couple of trips to the bathroom.

Once your body’s done dealing with that foreign entity, you’ll be good to go.

(Not to the bathroom again, I didn’t mean that…😄)


The niacin flush that causes the prickly heat & itching is usually gone in an hour or two, sometimes less.


Excessive caffeine-induced headaches may not go as quickly, it may take a few hours to pass completely.

Remember, caffeine’s half-life is somewhere around 5-6 hours, meaning that’s how long it takes to get rid of just half of the caffeine (31).

With caffeine-induced temporary high blood pressure, it’s hard to pinpoint an exact duration for it. This is because we’re all wired differently.


How to get rid of pre workout side effects?

Well, drinking some water can help the caffeine side effects a teeny bit, but you can’t flush it out out of your digestive system since it’s already in your bloodstream.

The other side effects mentioned in this article just need time to work through and are usually short-lived.

For something like insomnia though, that requires a lifestyle awareness change.

Meaning, make sure to respect how long a stimulant like caffeine can affect you. Keep the pre-workout supplement at least 8 hours away from your planned bedtime so it doesn’t affect your quality of sleep.


Does pre-workout cause anxiety?

Too much pre-workout containing caffeine can cause anxiety &/or agitation in people who have a preexisting mental condition or who are simply predisposed to reacting negatively to stress (32).

Caffeine acts as a stressor to the nervous system and can raise cortisol levels, so pre-workout formulas loaded with caffeine can definitely increase anxiety level in some people (33).


Is pre-workout bad?

Not all pre- & post-workout supplements are the same, they’re sold with all sorts of various ingredients in widely different doses, so some are helpful & some could be harmful.

Reading the labels of workout formulas and understanding what are safe & effective doses is a very important skill to have.


Wrapping Up

Related articles on heydayDo

Does Pre-Workout Work? Only With These 7 Ingredients

Benefits & Risks of Caffeine Anhydrous

12 Natural & Supplemental Creatine Alternatives

I hope this article on the side effects of pre-workout supplements and the ingredients that cause them is useful to you, and I wish you well on your fitness journey.

– greg


About The Author

heydayDo author Greg Simon

Hi, I’m Gregory Simon. Fitness training & nutrition researching since 1982. ISSN (International Society of Sports Nutrition) Pro Member. MBA, B.Sc.

Author. Surfer. Organic food grower. Congenital heart disease survivor (so far).

heydayDo.com is my wellness blog that’s about encouraging a healthy lifestyle as we age. 

I share my fitness training experience as well as the sports science research I’ve done on the many benefits strength building, exercise, & good eating habits offer us. 

I also write review articles after product testing and evaluating home gym equipment & fitness supplements.

My hope is that you’ll find useful or encouraging information here on my website that will benefit your unique fitness journey.

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