Why Does Pre-workout Make Me Tired?

Benedict Ang, CPT, PN1-NC
Published by Benedict Ang, CPT, PN1-NC | Staff Writer & Senior Coach
Last updated: March 26, 2024
FACT CHECKED by Dr. Kristy Dayanan, BS, MD
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Pre-workouts are quite useful supplements that I use myself and recommend to most of my colleagues. However, despite all its benefits, some people experience unexpected tiredness.

I decided to do my research, go through relevant scientific literature, and discuss everything with our dietitian so we can shed some light on this phenomenon.

Discover how your body reacts to pre-workout supplements and uncover the reasons why they can sometimes leave you feeling drained.

Quick Summary

  • To understand why pre-workouts can make you tired, it's essential to recognize the role of stimulants, especially caffeine, which can lead to fatigue when over-relied upon.
  • Pre-workouts are designed to enhance exercise performance, but excessive caffeine can result in a 'caffeine crash,' making users feel lethargic post-consumption.
  • Most pre-workout ingredients remain in the system for about 4-6 hours, which is typically when users might experience a crash.
  • In my opinion, while pre-workouts can be beneficial, it's crucial to find a balance and listen to one's body to avoid potential side effects and crashes.

Reasons Why Pre-workout Can Make You Tired

A woman experiencing tiredness

Pre-workouts often contain stimulants like caffeine, which initially boost energy but can lead to fatigue due to overuse. Ingredients like beta-alanine and l-citrulline enhance performance but may affect post-workout feelings. Personal experience with high-caffeine pre-workouts echoes this: an initial energy boost followed by an unexpected crash.

Higher caffeine content in pre-workouts may paradoxically lead to increased tiredness post-effects. Regularly consuming too much caffeine can result in a tolerance, further diminishing its energizing effects.

The physiology behind this is simple - caffeine is a central nervous system (CNS) stimulant that inhibits adenosine buildup in the brain (an energy metabolism product that causes tiredness) and affects the release of adrenaline and dopamine [1].

"Essentially, your body thinks caffeine molecules are binding to the parts of the brain where adenosine would normally attach to, causing increased alertness after drinking that cup of coffee. The downside to constant repeated exposure to caffeine causes the adenosine receptors to be less responsive to caffeine, and even develop more adenosine receptors, begging for more caffeine intake. It's this decrease in sensitivity that leads to caffeine tolerance."

- Mandy Enright, RD

Tiredness after consuming high-caffeine pre-workouts is due to the CNS striving for homeostasis, becoming tolerant to stimulants. This tolerance can cause a 'caffeine crash.' Adrenaline stimulation from pre-workouts gives an energy surge, but its subsiding can lead to fatigue.

Building tolerance to active ingredients like caffeine may reduce their effectiveness, emphasizing the need for cycling off these supplements. For a balanced approach, natural energy-boosting foods can be effective alternatives.

Learn More: Stim vs Non-Stim Pre-Workout (Which One Should You Take?)

How Does Pre-workout Crash Feel Like?

A woman feeling sick before workout

A pre-workout crash feels like an energy drain, leading to tiredness and lack of focus. This happens when the liver breaks down the supplement ingredients, revealing the previously masked adenosine to the brain, causing fatigue.

During one of my intense training sessions, I experienced this firsthand. Just an hour after taking my pre-workout, I felt a sudden energy drain, leading to tiredness and lack of focus. It's a sensation that's hard to shake off and can affect the rest of your day.

Most pre-workout ingredients stay in your system for about 4-6 hours, which is the period you will most likely experience a crash [2].

To avoid pre-workout crashes, select supplements that match your body's needs and are low on stimulants. Choose formulas with a balanced mix of ingredients to prevent crashes. Also, consider your sleep schedule and avoid late-night pre-workout use to reduce crash risks. A holistic approach to pre-workout supplementation helps maximize workouts without affecting overall well-being.

Most pre-workout supplements cause crashes because they contain caffeine in high doses, so if you’ve ever experienced sleepiness after consuming too much coffee, you are familiar with the feeling.

The odds of pre-workout caffeine crash dramatically increase if you have sleep deprivation or consume the pre-workout supplement for a late-night workout around bedtime. The symptoms usually last a few hours, but in some cases, they can go on for a few weeks, as per NCBI [3].

How To Avoid the Crash?

A fit woman doing stretching before workout

I've learned from my experiences that moderation is key. To avoid a pre-workout crash, I've started following some simple rules, including taking pre-workout in lower doses, ensuring I eat well before my training, occasionally pausing my pre-workout use, and steering clear of additional stimulants.

Many pre-workout supplements have high amounts of stimulative ingredients a lot of people can't handle well, that's why we recommend you look for a stim-free pre-workout.

If you're experiencing crashes after taking pre-workout, try reducing the amount and monitor changes. Remember, pre-workouts provide temporary energy for high-intensity workouts but don't replace the need for a high-calorie diet, especially carbohydrates. When the pre-workout effect fades, the importance of carbs becomes evident.

“Putting the wrong things in your tank before you exercise can leave you lethargic, crash your system, or cause wicked cramps, and going on empty can do the same.”

- Jim White, RD

Therefore, try to eat plenty of calories on workout days (even on a weight loss plan) and avoid taking pre-workout on an empty stomach as ingredients will get absorbed much faster, contributing to a harder crash.

To counteract pre-workout tiredness due to tolerance, consider taking a break from stimulants for one to two weeks. This period allows your body to regenerate energy reserves and refresh adenosine receptors. During this break, try to avoid caffeine and other stimulants like energy drinks or coffee.

Speaking of other stimulants, you should be aware that taking pre-workout should mean avoiding other stuff that similarly affects your nervous system (like some medical drugs) [4]. This will make you less likely to hit your stim threshold and induce the body's stress response and potential side effects.

When used as directed, pre-workouts boost energy and blood flow. However, overuse can lead to side effects like headaches and insomnia. Therefore, a pre-workout is a great servant but a bad master, so make sure you opt for the ones we tried and tested for safety and efficacy:

Some of the top products we tested provided some impressive results for our clients, so check them out to find the one that best suits your needs.


How Quickly Do You Build a Tolerance to a Pre-workout?

You build a tolerance to a pre-workout pretty quickly since it usually takes only a few days for your body to adapt to stimulants.

That's the period needed to build tolerance for constant caffeine levels in your blood, with caffeine being the most common ingredient in pre-workouts.

Eventually, you lose the pre-workout rush because taking the same formula daily may cause cell receptors to become saturated and nerve endings desensitized, reducing the impact of those effects. In case of tolerance, you should stop consuming stimulant ingredients for a week or two.

Why Does My Pre-workout Make Me Light-headed?

Your pre-workout can make you lightheaded if you take it on an empty stomach because of the low blood glucose. It can also happen due to certain ingredients and their side effects Citrulline malate, for example, can lower your blood pressure and cause dizziness. Caffeine, on the contrary, may provoke high-blood pressure or dehydration, both of which make you feel light-headed.

Should I Take Pre-workout If I'm Tired?

You may take pre-workout when you're tired. However, it's generally better to address the underlying cause (like lack of sleep or poor nutrition) rather than relying on pre-workout supplements for energy.


  1. https://go.gale.com/ps/i.do
  2. https://www.ncbi.nlm.nih.gov/books/NBK223808/
  3. https://www.ncbi.nlm.nih.gov/books/NBK519490/
  4. https://www.drugs.com/drug-class/cns-stimulants.html
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About The Author

Benedict Ang, CPT, PN1-NC
Staff Writer & Senior Coach
Benedict Ang, CPT, PN1-NC is an ex-National Soccer player turned MMA and Kickboxing champion, with ACE CPT and PN1-NC certifications. His advice is rooted in education and experience, ensuring that readers receive scientific and battle-tested insights. His mission is to empower his clients and readers to realize their potential and become the best versions of themselves.
Learn more about our editorial policy
Dr. Kristy June Dayanan, BS, MD is an author with a BS degree from University of the Philippines and an MD from University of Perpetual Help System. Her ability to simplify medical science complexities and dietary supplement jargon for the average reader makes her a valued medical fact checker and reviewer.
Learn more about our editorial policy
Dr. Harshi Dhingra, MBBS, MD is a published peer-reviewed author and renowned physician from India with over a decade of experience. With her MBBS from Bharati Vidyapeeth and an MD from Rajiv Gandhi University, she actively ensures the accuracy of online dietary supplement and medical information by reviewing and fact-checking health publications.
Learn more about our editorial policy

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