What Happens to Your Body When You Take Pre-Workout

Pre-workout supplements can support energy, strength, and endurance during exercise, but they also come with several potential side effects.

Mar. 13, 2026 at 1:52pm

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Pre-workout supplements have become a popular product for boosting energy, supporting muscle growth, and improving endurance during exercise. The common ingredients in pre-workout, like caffeine and beta-alanine, can provide benefits like increased alertness, muscle endurance, and improved cardio performance. However, these ingredients can also cause side effects such as nausea, heart palpitations, and tingling sensations. Experts recommend starting with a low dose, watching your total caffeine intake, and avoiding pre-workouts if you have underlying conditions.

Why it matters

Pre-workout supplements are widely used by athletes and fitness enthusiasts, but it's important to understand both the potential benefits and risks associated with these products. This information can help consumers make informed decisions about whether pre-workouts are right for them and how to use them safely.

The details

The caffeine in pre-workouts can make you feel more alert and energized by blocking adenosine receptors in the brain and triggering the release of adrenaline. Caffeine and ingredients like beta-alanine can also help your muscles work harder for longer by delaying fatigue and the 'proverbial 'burn' sensation.' For cardio, the caffeine and compounds like citrulline malate may improve endurance by enhancing respiratory function and blood flow. However, pre-workouts can also cause side effects like skin reactions, nausea, heart abnormalities, dizziness, and insomnia, especially if you exceed the recommended daily caffeine limit.

  • The 2019 survey of 1,045 people taking pre-workout found that more than half (54%) reported side effects.

The players

Alexander LeRitz

A registered dietitian and sports nutritionist at JM Nutrition.

Brian Cole

A sports medicine surgeon, the head team physician for the Chicago Bulls, and a team physician for the Chicago White Sox.

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What they’re saying

“When taking pre-workout supplements, it is a good idea to watch your intake of stimulants throughout the rest of the day, which might look like skipping those morning coffees to keep overall caffeine intake below the recommended daily threshold.”

— Alexander LeRitz, Registered Dietitian and Sports Nutritionist (health.com)

“Pre-workout isn't recommended for people under age 18 or during pregnancy. It's also not advised for people with pre-existing conditions, such as heart disease, arrhythmia, hypertension, anxiety, liver disease, or kidney disease, because the ingredients in pre-workout may worsen baseline symptoms.”

— Brian Cole, Sports Medicine Surgeon (health.com)

The takeaway

While pre-workout supplements can provide benefits like increased energy, strength, and endurance, it's important to be aware of the potential side effects and use them cautiously. Starting with a low dose, monitoring your total caffeine intake, and avoiding pre-workouts if you have certain health conditions can help ensure a safer experience.