The 10 Most Common Pre-Workout Side Effects

To paraphrase the great American writer, Mark Twain, “Too much of anything is bad, but too much pre-workout is barely enough.” Twain originally chose whiskey as the beverage of choice, but there’s a good chance he’d find the humor in the near-obsession some modern day “fitness” enthusiasts have with potent pre-workout concoctions.

Judicious use of a pre-workout can certainly lead to higher intensity sessions that last longer and deliver a greater muscle-building, fat-burning stimulus. However, all pre-workout formulas are designed with different ingredients in different doses, so “one scoop” of something isn’t always comparable to “one scoop” of a different mixture.

Knowing what you’re taking, how much, and, more importantly, how your body reacts to those ingredients is essential to get the best results. Before you start your next training session with a high-potency pre-workout, here’s how to know the possible side effects you might encounter.

Editor’s Note: The following information is meant to be informative in nature, but should not be taken as medical advice. The content presented is not intended for use as diagnosis, prevention, and/or treatment of health problems. It is not a substitute for consulting a qualified medical professional.

Pre-Workout Side Effects

Most Common Pre-Workout Ingredients

Pre-workouts are technically a general category of supplements made up of different mixes with a variety of ingredients. However, some similar types of ingredients tend to pop up across different formulas.

Stimulants

Possibly the most well-known and, for some, most desired, type of ingredient is a straightforward stimulant to bolster physical and mental energy. Caffeine, tyrosine, yohimbine, and theacrine are some of the most common sources of stimulants.

While the majority of pre-workouts contain some form of stimulant, there are many non-stimulant pre-workout mixes that can be just as effective while omitting key energizing ingredients.

Blood Flow Enhancers

Many pre-workouts contain ingredients designed to improve blood circulation throughout the body. This can help to improve “the pump” while training and may increase endurance. Common nitric oxide boosters, sometimes called “NO2 boosters,” include arginine, citrulline, and betaine (not to be confused with beta-alanine, which is an unrelated ingredient with different effects).

Endurance Support

Many pre-workouts improve your physical endurance during a training session. This can either occur physiologically, by improving your body’s capacity for sustained output, or by decreasing your sense of fatigue so you essentially “feel less tired” as a workout progresses. Common endurance boosters include highly branched cyclic dextrins (which are actually a carbohydrate source rather than a specific supplement) and beta-alanine.

Benefits of Pre-Workout

When it’s time for a pre-workout to deliver results, many formulas knock the ball out of the park. Pre-workouts are popular largely because they are effective. Here are some of the most noticeable benefits.

Increased Energy and Alertness

Whether by stimulants, improved blood flow, or other mechanisms, pre-workouts typically get you “fired up” headed into a training session. This can be useful if you train after a tiring day at work, if you’re dragging in a slow gear before your first repetition, or if you head into a workout when your mental focus is less than 100%.

Increased Power and Strength

Pre-workouts can have a direct impact on your strength output during a given workout. (1) By helping to recruit more muscle units, exciting your central nervous system, or improving your muscles’ ability to contract, pre-workouts may help to move more weight for more reps. Over time, this can contribute to greater strength gains and muscle mass.

Improved Blood Flow

Many pre-workout formulas increase total-body circulation. This improved blood flow may help with general alertness and energy, greater motivation to train, increased physical endurance, and an improved muscle pump. The pump, in particular, has been associated with a greater muscle-building stimulus. (2)

Enhanced Endurance

The ability to perform longer workouts without decreasing output has been a time-tested recipe for improved fitness, strength, and performance.

Many pre-workouts help to improve endurance during a training session, either by decreasing your body’s sense of fatigue or by encouraging a sustained power output. This can be achieved either with improved recovery between sets or with better fueled performance at a higher intensity.

10 Potential Side Effects

Your central nervous system (CNS) is essentially the way your brain communicates with, and activates, your muscles during exercise. Your CNS can become more stressed when training intensity or volume is increased, which can negatively affect overall recovery and performance. (3)

Because pre-workouts allow you train train harder and longer — with greater intensity and potentially more volume — you may be at risk over overstressing your CNS with excessive use.

Impaired Sleep

Perhaps the most “obvious” potential drawback of a stimulant-laden pre-workout is interrupted sleep and potential insomnia. This is primarily an issue with stimulant-heavy pre-workouts (those which include caffeine or other stimulants in their formula), particularly if they are taken in the afternoon or evening.

For example, taking a pre-workout around 5 p.m. for an afterwork training session is much more likely to cause sleep problems than a pre-workout taken at 7 a.m. for an early morning workout. However, individual sensitivities and total daily caffeine intake (from coffee, tea, soda, etc.) can be a factor.

Nausea

Sometimes simple hard training can lead to nausea. Many experienced lifters have needed to visit the “puke bucket” during high-rep squats, but potent pre-workout formulas might turn even an average workout into a sour stomach fiasco.

Whether it’s due to an overload of stimulants, an excessive workload, or just a mix of various ingredients swirling around your gut, a strong pre-workout could leave you feeling queasy, which would ultimately interrupt your training session. Some research suggests this is actually one of the most common side effects some lifters experience after taking a pre-workout. (4)

GI Upset

Similar to nausea, some lifters may experience gastric distress (upset stomach and/or bowel issues) after taking a pre-workout, often due to high-dose stimulants or related ingredients. This can severely interrupt a training session, often derailing a workout before it’s even begun. In extreme cases, it may be severe enough to force a lifter to abandon a workout entirely.

Attenuation

While stimulant-based pre-workouts can be highly effective for improving strength, power, and endurance, they can also deliver gradually diminishing results if used in excess. The body can develop a tolerance to stimulants, including caffeine, making their beneficial effects less impactful over time. (5)

To ensure maximum impact, aim to use a pre-workout no more than every other day, rather than every workout. If you frequently consume significant amounts of caffeine during a regular day, consider cutting back or using a pre-workout even less frequently. This should allow the formula to deliver a more noticeable benefit. (6)

Dehydration

A notable, but relatively easily preventable, side effect of pre-workouts is dehydration. By prompting a more challenging workout, some lifters may become more depleted during a high intensity training session via increased sweating and the loss of basic nutrients. (7)

This may not necessarily be accounted for with sufficient intra-workout hydration. Dehydration can lead to an overall decrease in power and endurance, making the workout counterproductive.

Headache

Another possible side effect of pre-workout, which may be noticeable sooner rather than later during some sessions, is a straightforward headache. Many pre-workout ingredients increase overall blood flow which can be beneficial to muscular performance, but can also be contraindicated in a person who is already experiencing high blood pressure. (8)

If you’re currently dealing with hypertension, double-check your pre-workout formula for ingredients which may exacerbate the issue such as arginine, citrulline, and other purported “nitric oxide boosters.”

Increased Heart Rate

Pre-workouts may increase a lifter’s heart rate, either relatively directly through stimulant-based ingredients or by supporting a high degree of training intensity. In lifters with hypertension or other cardiovascular risks, an increased heart rate may present a potential danger.

While exercise, in itself, may raise a person’s heart rate, the addition of a pre-workout may bring it to inappropriate or unexpected levels.

Skin Reaction

A relatively minor side effect, but no less distracting, is a “tingling” or itching skin sensation after taking a pre-workout. This can be particularly common in formulas which contain beta-alanine — a supplement typically associated with a “flushing” of the skin.

Some research associates the beta-alanine reaction with an overstimulation of nerve endings, rather than a symptom of acute allergic reaction. (9) Regardless, the skin flush may be distractingly uncomfortable, despite being considered a “successful sign” that the supplement may be working.

Medication Interaction

Many nutritional supplements carry the risk of potential interactions with prescription medications. Pre-workout formulas are no different and should be approached with adequate consideration.

Several individual ingredients common to pre-workout mixes are considered “contraindicated” when taking key categories of medications. For example, NO2 boosters such as arginine or citrulline may have an additive effect in people taking certain medications for erectile dysfunction. (10)

Similarly, the amino acid tyrosine (sometimes used in pre-workouts for improved mental focus) may interact with certain prescribed antidepressants and may lead to increased blood pressure and related problems.

Pre-Workout with Care

Pre-workout formulas can be distinctly useful when used strategically. However, like any supplement, there are also potential side effects to be aware of. Mistaking pre-workout formulas as being entirely risk-free would be a short-sighted error. Make sure you know what you’re taking and why you’re taking it. Once you have those details sorted out, you’ll be better prepared to anticipate and mitigate any potential side effects, leading to greater results overall.

References

1. Martinez, N., Campbell, B., Franek, M., Buchanan, L., & Colquhoun, R. (2016). The effect of acute pre-workout supplementation on power and strength performance. Journal of the International Society of Sports Nutrition, 13, 29. https://doi.org/10.1186/s12970-016-0138-7
2. Schoenfeld, Brad J. PhD, CSCS, CSPS, NSCA-CPT1; Contreras, Bret MA2. The Muscle Pump: Potential Mechanisms and Applications for Enhancing Hypertrophic Adaptations. Strength and Conditioning Journal 36(3):p 21-25, June 2014. | DOI: 10.1097/SSC.0000000000000021
3. Zając, A., Chalimoniuk, M., Maszczyk, A., Gołaś, A., & Lngfort, J. (2015). Central and Peripheral Fatigue During Resistance Exercise – A Critical Review. Journal of human kinetics, 49, 159–169. https://doi.org/10.1515/hukin-2015-0118
4. Jagim, A. R., Camic, C. L., & Harty, P. S. (2019). Common Habits, Adverse Events, and Opinions Regarding Pre-Workout Supplement Use Among Regular Consumers. Nutrients, 11(4), 855. https://doi.org/10.3390/nu11040855
5. Boulenger, J. P., Patel, J., Post, R. M., Parma, A. M., & Marangos, P. J. (1983). Chronic caffeine consumption increases the number of brain adenosine receptors. Life sciences, 32(10), 1135–1142. https://doi.org/10.1016/0024-3205(83)90119-4
6. Addicott, M. A., & Laurienti, P. J. (2009). A comparison of the effects of caffeine following abstinence and normal caffeine use. Psychopharmacology, 207(3), 423–431. https://doi.org/10.1007/s00213-009-1668-3
7. Judge, L. W., Bellar, D. M., Popp, J. K., Craig, B. W., Schoeff, M. A., Hoover, D. L., Fox, B., Kistler, B. M., & Al-Nawaiseh, A. M. (2021). Hydration to Maximize Performance and Recovery: Knowledge, Attitudes, and Behaviors Among Collegiate Track and Field Throwers. Journal of human kinetics, 79, 111–122. https://doi.org/10.2478/hukin-2021-0065
8. Cameron, M., Camic, C. L., Doberstein, S., Erickson, J. L., & Jagim, A. R. (2018). The acute effects of a multi-ingredient pre-workout supplement on resting energy expenditure and exercise performance in recreationally active females. Journal of the International Society of Sports Nutrition, 15, 1. https://doi.org/10.1186/s12970-017-0206-7
9. Liu, Q., Sikand, P., Ma, C., Tang, Z., Han, L., Li, Z., Sun, S., LaMotte, R. H., & Dong, X. (2012). Mechanisms of itch evoked by β-alanine. The Journal of neuroscience : the official journal of the Society for Neuroscience, 32(42), 14532–14537. https://doi.org/10.1523/JNEUROSCI.3509-12.2012
10. El-Wakeel, L. M., Fouad, F. A., Saleem, M. D., & Saber-Khalaf, M. (2020). Efficacy and tolerability of sildenafil/l-arginine combination relative to sildenafil alone in patients with organic erectile dysfunction. Andrology, 8(1), 143–147. https://doi.org/10.1111/andr.12671

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