Pre-Workout Side Effects: What Causes Them and How to Avoid Them

Most pre-workout side effects come from caffeine and beta-alanine, and most are dose problems. The common ones are jitters, a racing heart or palpitations, tingling skin, nausea, headaches and poor sleep. In the largest survey of pre-workout users, more than half reported at least one side effect, and many were taking more than one scoop. Serious problems are rare and usually involve very high doses, stimulant stacking, banned ingredients or an existing heart condition.

A pre-workout is not one ingredient but a blend, often with a dozen components and doses hidden in a “proprietary blend”. So the useful question is not “is pre-workout safe?” but which ingredient causes which effect, and how much is too much.

How this article was put together

I read the main survey of pre-workout users (Jagim and colleagues, 2019), a 2025 integrative review of pre-workouts and cardiovascular health, FDA guidance on caffeine, and the ISSN position stand on beta-alanine, listed under Sources. I have not run any trial myself. This is general information, not medical advice.

What the research shows

In a 2019 survey of 872 pre-workout users published in Nutrients, the products contained on average about 254 mg of caffeine and 2 g of beta-alanine per serving. Over half of respondents (54%) reported side effects, most often skin reactions, nausea and heart palpitations. Importantly, many said they took more than the recommended serving, which can push caffeine well past what most people tolerate.

A 2025 integrative review in the Journal of Cardiovascular Development and Disease found that controlled trials of pre-workouts at labelled doses mostly showed no lasting change in heart rate or blood pressure, while the case reports of serious cardiac events typically involved very high caffeine intakes, multiple stimulants, or people with existing conditions. In a large survey of US service members, users of a popular caffeine and beta-alanine pre-workout reported palpitations or increased heart rate (11%), tingling (13%), insomnia and nausea.

The side effects, one by one

Jitters, anxiety and a racing heart

Caffeine is the main driver. Many pre-workouts contain 150–350 mg per scoop, the same as two to four cups of coffee, taken in one go. The FDA cites 400 mg a day as an amount not generally associated with negative effects in healthy adults, but that includes your coffee, energy drinks and any fat burner. Other stimulants such as synephrine (bitter orange), yohimbine or high-dose green tea extract add to the effect.

Tingling, itching or flushing

Usually beta-alanine, which activates itch receptors in the skin. It is harmless and fades within about an hour; see beta-alanine itching. A hot, red flush is more often niacin (vitamin B3).

Nausea, stomach upset and diarrhoea

Large doses on an empty stomach, caffeine, magnesium, and sugar alcohols in sweetened products are the usual causes. Taking the drink with more water, or a small snack, often helps.

Headaches

Caffeine can trigger headaches, and so can caffeine withdrawal on rest days. Nitric-oxide ingredients such as citrulline and arginine widen blood vessels, which can cause headaches in some people. Dehydration adds to both.

Poor sleep

Caffeine has a half-life of around five hours, so an evening pre-workout can still be active at bedtime. Mayo Clinic sports researchers suggest avoiding caffeine after about 2 or 3 p.m. if sleep suffers.

Banned or risky ingredients

Some products, mostly sold online, have been found to contain stimulants that are not legal in supplements, such as DMAA, which the FDA has warned can raise blood pressure and lead to heart problems. Proprietary blends that hide doses make it harder to know what you are taking. For drug-tested athletes, any pre-workout without NSF Certified for Sport or Informed Sport is a risk.

Long-term effects

There are few long-term studies of pre-workouts as such. Trials lasting four to eight weeks at labelled doses mostly found no harmful changes in blood pressure, heart rate, liver or kidney markers. The realistic long-term issues are caffeine tolerance and dependence (needing more for the same effect, headaches without it) and chronically poor sleep, which undermines recovery and the training the pre-workout was supposed to help.

Who should avoid pre-workouts or ask a doctor first

• People with heart rhythm problems, high blood pressure or heart disease.
• Anyone pregnant or breastfeeding.
• People with anxiety or panic disorders, or who are sensitive to caffeine.
• Anyone taking stimulant medication (for example for ADHD), MAO inhibitors or other drugs that interact with caffeine.
• Teenagers.

How to reduce side effects

• Start with half a scoop to test your tolerance, and never take more than one serving.
• Count your total caffeine for the day, including coffee and energy drinks, and stay under 400 mg.
• Avoid proprietary blends that do not list the dose of each ingredient.
• Do not stack stimulants, such as a pre-workout plus a fat burner; see do fat burners work?
• Train earlier or use a stimulant-free pre-workout in the evening.
• Choose a certified product (NSF Certified for Sport or Informed Sport) if you want to be sure of the contents.

A simpler alternative

Much of what a pre-workout does can be covered by a cup of coffee before training and creatine taken daily, which has a far larger evidence base and few side effects. See creatine side effects and the best creatine powders compared.

Common questions

What are the side effects of pre-workout?

Most commonly jitters, a racing heart or palpitations, tingling skin, nausea, headaches and poor sleep. They are mostly caused by caffeine and beta-alanine and depend on the dose.

Is pre-workout bad for your heart?

At labelled doses, trials in healthy adults mostly show no lasting change in heart rate or blood pressure. Serious cardiac events are rare and usually involve very high caffeine intakes, multiple stimulants or existing heart conditions.

Why does pre-workout make me itchy?

Beta-alanine activates itch receptors in the skin. It is harmless and fades within about an hour. Smaller doses reduce it.

Why does pre-workout make me feel sick?

Usually a large dose on an empty stomach, too much caffeine, or sweeteners and magnesium. Try half a scoop with more water or a small snack.

What are the long-term side effects of pre-workout?

Long-term data are limited. The main known issues are caffeine tolerance and dependence and poor sleep. Short trials at labelled doses have not found harmful changes in heart, liver or kidney markers.

Sources

• Jagim AR et al. Common habits, adverse events, and opinions regarding pre-workout supplement use among regular consumers. Nutrients. 2019.
• Pre-workout supplements and their effects on cardiovascular health: an integrative review. J Cardiovasc Dev Dis. 2025.
• US FDA — Spilling the beans: how much caffeine is too much?
• Mayo Clinic Press — Preworkout supplements: what’s safe, what should you avoid?
• Trexler ET et al. ISSN position stand: beta-alanine. J Int Soc Sports Nutr. 2015.