What Does Pre-Workout Do to Your Body Before Exercise? (2025)

Multi-ingredient pre-workout supplements (MIPS), also called "pre-workout," are a class of dietary supplements intended to be taken before exercise, and they typically contain a blend of ingredients such as caffeine, amino acids, creatine, and beta-alanine. Pre-workout supplements claim to increase energy, enhance performance, and improve focus, but be aware of the potential risks and side effects when taking these supplements.

Jump to Key Takeaways.

1. Increased Energy/Delayed Fatigue

Limited research has shown that some participants self-report feeling improvements in energy and fatigue levels with pre-workout supplements. Pre-workout supplements often contain caffeine or other stimulants, such as guarana. When taken 30 to 60 minutes before a workout, they can give a temporary energy boost during exercise.

High doses of caffeine, generally considered between 5 and 13 milligrams (mg) of caffeine per kilogram (kg) of body weight (mg/kg), can produce side effects, such as upset stomach, sleep difficulties, and confusion. Smaller doses, such as 3 mg/kg, can still be effective with fewer side-effects.

The body produces beta-alanine, an amino acid, which works with other chemicals in the body to make carnosine. Carnosine helps maintain the pH level of muscles, which can help delay fatigue during high-intensity exercise. Research on the beta-alanine in many pre-workout supplements have been inconclusive regarding its efficacy.

2. Enhanced Performance

The caffeine in pre-workout supplements can help enhance performance by increasing endorphin release, reducing perception of exertion while exercising, and improving neuromuscular function, vigilance, and alertness.

Some pre-workout supplements can contain levels of caffeine above the recommended daily tolerable upper limit (UL) of 400 mg. Caffeine powder is sometimes marketed as a stand-alone pre-workout supplement, but it should be avoided. The FDA recommends against its use as even a very small amount can lead to a lethal caffeine overdose.

Pre-workout supplements often contain beta-alanine and creatine. Beta-alanine has been found to improve exercise performance, especially for high-intensity exercise lasting one to four minutes, when dosed at 4–6 grams (g) per day for two to four weeks. Beta-alanine is often included in pre-workout supplements, but not necessarily at that dosage, or effective in isolated use. Creatine has been found to positively affect high-intensity exercise performance with a loading period of 20 g per day, followed by a regular maintenance consumption of 3–5 g per day.

3. Improved Cognition and Focus

Pre-workout supplements that contain caffeine may improve levels of focus and alertness, according to research findings based on users' self-reports. Initial studies also show promising results suggesting that pre-workout supplements may help with reaction time, selective attention, and cognitive processing.

What Is in Pre-Workout Supplements?

Pre-workout ingredients vary by brand. These powdered supplements are usually mixed with water and then consumed. Generally, the powdered mixture consists of ingredients, such as:

• Amino acids
• Beta-alanine
• Caffeine
• Creatine

Ingredients are often classified as being part of a "proprietary blend," in which the amount of each ingredient is not disclosed to the consumer. This imprecise labeling makes it difficult to determine if ingredient amounts are reliably accounted for, how brands compare against each other, and whether the product is safe and effective.

Tips for Taking Pre-Workout Supplements

Some things to keep in mind if you choose to use pre-workout supplements include:

• Always talk to your healthcare provider first: These supplements, and their ingredients, are not appropriate for everyone. For example, people with kidney disease and those with bipolar disorder should not use creatine supplements.
• Avoid the "dry-scooping" trend: "Dry scooping" is a social media trend that involves swallowing a scoop of dry pre-workout supplement followed by a swig of water. Not only does this have no added benefits, it's dangerous because the powder can be inhaled causing choking and respiratory problems. Mix the powder with fluid as directed.
• Consider your goals: Different pre-workout supplement products have different intended effects. Consider factors such as whether the product boosts energy and endurance, aids in bulking up, or both.
• Look at all the ingredients: Are there added sugars or other ingredients you want to avoid for dietary reasons or preference?
• Research products well: Pre-workout supplements may be poor quality, have inaccurate or uninformative labeling, or not do what they claim to. They may also contain contaminants. Look for reputable brands that have been third-party tested for quality. Organizations such as NSF and U.S. Pharmacopeia (USP) verify potency, label accuracy, and the presence of harmful ingredients.
• Adhere to recommended dosages: Read the instructions, and do not go above recommended dosages. If possible, find out the actual amounts of the ingredients in the supplements, such as caffeine, so you don't take too much. It's a good idea to start small to see how your body reacts.
• Check the recommended timing: Pre-workout supplements are typically taken between 30 and 60 minutes before exercising. If yours contain stimulants, like caffeine, be careful what time you take them so they do not affect your sleep.

Who Should Skip Pre-Workouts?

Talk to your healthcare provider before taking pre-workout supplements, particularly if you have certain health concerns, such as bipolar disorder, kidney disease, or risk factors for liver damage.

Some of the potential risks involved with pre-workout supplements are:

• Increased total body water with creatine supplementation, which could affect performance in activities in which body mass is a factor
• Potential for large amounts of caffeine, which can have harmful side effects such as anxiety, tremors, chest pain, heart palpitations, nausea, headaches, and seizures
• Potential for novel ingredients that haven't been properly studied
• Potential for tolerance and/or withdrawal symptoms with regular use
• Potential for unknown ingredients and amounts, mislabeling, benefit misrepresentation, and product contamination, which could be toxic, lead to overdose, cause allergic reactions, cause a failed drug test, or have adverse effects with other medications or supplements
• Unknown long-term use effects, which could include kidney damage, high blood pressure (hypertension), or disrupted sleep patterns

Key Takeaways

• Pre-workout supplements are multi-ingredient supplements taken 30 to 60 minutes before a workout. They typically contain ingredients such as caffeine, amino acids, creatine, and beta-alanine.
• Pre-workout supplements may have beneficial effects on energy, fatigue levels, performance, and focus, but more research is needed on their potential.
• Pre-workout supplements are not appropriate for everyone, and can have risks and side effects. Always talk to your healthcare provider before taking supplements, including pre-workout supplements.