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

Isaac Robertson
Published by Isaac Robertson
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: April 9, 2023
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Pre-workouts are quite useful supplements that I recommend to most of my clients. However, despite all its benefits, some people experience unexpected tiredness.

Many of my clients 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

  • Tiredness accumulates with time and hits back hard once stimulants get worn off.
  • The pre-workout crash is equivalent to a caffeine crash and causes sleepiness, tiredness, irritability, and inability to concentrate.
  • To avoid the pre-workout crash, you should take smaller doses and eat before consuming formula or occasionally cycle different stimulants.

Reasons Why Pre-workout Can Make You Tired

A tired woman holding a supplement drink

There are several reasons pre-workout can make you tired, but stimulants are the main culprit.

The role of stimulants in pre-workout supplements is to increase alertness, concentration, and energy levels.

With additional ingredients that can increase blood flow and improve strength and endurance (like beta-alanine, l-citrulline, or creatine), pre-workout is designed to enhance your overall exercise performance.

The most common stimulant in pre-workout supplements by far is caffeine.

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 high doses of 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.

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

Pre-workout crash feels like a rapid energy drain, making you feel tired, sleepy, and exhausted with a lack of concentration.

This side effect happens when pre-workout supplement ingredients are all eventually broken down by liver enzymes.

That’s when the accumulated adenosine (beforehand masked with stimulants) becomes 'visible' to the brain, resulting in instant tiredness, irritability, nausea, or headache.

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.

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].

Related Article: Should I Take Pre-workout if I’m Tired?

How To Avoid the Crash?

A woman holding a tumbler

To avoid a pre-workout crash, you should follow simple rules, including taking pre-workout in lower doses, eating well, pausing pre-workout use, and keeping off 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.


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.

What is The Best Way to Use Pre-workout?

Taken as recommended, pre-workouts can provide numerous benefits like increased blood flow and more energy, but excessive use can lead to headaches, anxiety, insomnia, tolerance, and so on.

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.


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