Why Does Pre-workout Make Me Tired? Answered by a Dietitian

Benedict Ang, CPT, PN1-NC
Published by Benedict Ang, CPT, PN1-NC | Staff Writer & Senior Coach
Last updated: November 28, 2023
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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.

Many of my colleagues don’t get how this opposite effect happens and why, mainly because they don't understand the mechanism behind pre-workout supplements' metabolism.

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.

Here is what I found out.

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.
  • 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 tired woman holding a supplement drink

Stimulants, especially caffeine, are the primary reasons pre-workouts can cause tiredness.

While they boost alertness and energy, over-reliance can lead to fatigue.

Other ingredients like beta-alanine and l-citrulline enhance performance but can also play a role in how you feel post-workout.

I remember the first time I took a pre-workout with a high caffeine content. The initial energy surge was incredible, but the crash afterward was unexpected.

However, the more caffeine per serving pre-workout contains, the higher the possibility of it making you tired after the effects wear off.

It may sound counterintuitive, but constant too much caffeine may build a caffeine tolerance, which diminishes its ability to energize you even further.

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

So the reason for tiredness lies in our CNS’s goal to maintain ‘homeostasis’ (strive to keep our internal body processes stable while adjusting to changing external conditions).

By switching-off reactions to stimulants (external conditions), CNS ‘ignores’ it and restores the homeostasis.

This might be the answer as to why you feel tired and lethargic after pre-workout or caffeine consumption.

Therefore, constant intake of pre-workouts with high caffeine doses may cause the body to build tolerance, making you feel less energized or causing sudden tiredness known as a 'caffeine crash.'

You can eliminate this risk by using one of these caffeine-free pre-workouts that we tried and love.

While pre-workouts are designed to give you that much-needed boost, it's essential to understand the role of adrenaline. These supplements can stimulate adrenaline production, giving you an initial surge of energy. However, once this adrenaline rush subsides, it can leave you feeling more fatigued than before, making it crucial to balance your intake and listen to your body's signals.

Consistent use of pre-workouts can lead to another unexpected issue: building a tolerance to its active ingredients. Over time, as your body becomes accustomed to components like caffeine, you might find that the same dose no longer provides the energy kick it once did. This reduced effectiveness can inadvertently lead to feelings of tiredness post-workout, emphasizing the importance of occasionally cycling off these supplements.

If you're wary of the potential crashes associated with pre-workouts, consider natural alternatives. Foods like bananas, oats, or even a cup of black coffee can offer a sustainable energy boost without the subsequent drop in energy levels. Exploring these options can provide a more balanced approach to pre-exercise nutrition.

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

How Does Pre-workout Crash Feel Like?

A woman resting from exhaustion with supplement drink beside her

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].

You will notice the urge to go to bed because your body feels tremendously weak.

To mitigate the risk of pre-workout crashes, it's crucial to carefully select supplements tailored to your body's needs and sensitivity.

Opting for pre-workout formulas that provide a balanced blend of performance-enhancing ingredients while minimizing stimulant overload can help avoid the unpleasant crash phenomenon.

Additionally, paying attention to your sleep schedule and avoiding late-night consumption of pre-workout supplements can significantly reduce the chances of experiencing post-workout crashes.

Prioritizing a holistic approach to pre-workout supplementation will ensure you maximize your workouts without compromising your 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 [3].

How To Avoid the Crash?

A woman holding a tumbler

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.

Therefore, if you experience pre-workout crashes, you should consider consuming less pre-workout and keep track if this side effect decreases.

If crashes continue, keep in mind that high-intensity workouts demand high-calorie intake, and pre-workout could jump in only temporarily to ensure we get enough energy to get through the session.

When pre-workout wears off, you instantly become aware of the carbs' importance.

“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.

Since one of the reasons pre-workout makes you tired may be the tolerance, the efficient method might also be taking a break from stimulants and allowing your body to regenerate its energy reserves and refresh your adenosine receptors.

The gap should last about a week or two, and during this cycle, you should try to avoid caffeine and other stimulants (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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