Why does pre-workout cause heart palpitations or anxiety?
Caffeine blocks adenosine receptors and raises adrenaline, heart rate and alertness, and pre-workouts often deliver 150–300 mg at once, sometimes with other stimulants. Palpitations and anxiety rise with dose and with personal sensitivity. Cut the dose, avoid stacking, and see a doctor for chest pain, fainting or a heartbeat that does not settle.
- Caffeine blocks adenosine receptors, raising alertness, heart rate and blood pressure.
- ISSN: about 9 mg/kg gives high side-effect rates without extra benefit; 3–6 mg/kg is the useful range.
- EFSA: up to 200 mg at once and 400 mg a day is safe for healthy adults.
- Published caffeine for pre-workouts sold in SA ranges from 150 mg to 300 mg a scoop (the 200 mg and 300 mg figures come from US or global brand pages).
- Seek emergency care (10177 or 112) for chest pain, fainting or seizures.
Why does pre-workout cause palpitations and anxiety?
Most of the effect is caffeine. It blocks adenosine receptors in the brain, which reduces the feeling of fatigue and increases arousal. In the body that comes with a faster heart rate, a rise in blood pressure and a jittery feeling. The ISSN lists jitteriness, raised heart rate, anxiety, stomach upset and disturbed sleep as dose-related side effects.
Which factors make it worse?
- Dose. Published doses for tubs sold in SA run from 150 to 300 mg a scoop (300 mg from a global, non-SA page), and some tubs publish none. About 9 mg/kg gives high side-effect rates without extra performance benefit; for a 70 kg person that is roughly 630 mg.
- Sensitivity. Body size, genetics, regular caffeine intake, sleep debt and anxiety disorders all change your response.
- Stacking. A scoop plus coffee, an energy drink or a fat burner. EFSA considers up to 200 mg at once and 400 mg a day safe for healthy adults.
- Other stimulants. Some products add synephrine, yohimbine, DMAA-type compounds or other stimulants, which add to the cardiac load. See is DMAA banned.
- Empty stomach, heat and dehydration. These make the effects feel stronger.
- Dry scooping. A concentrated hit goes in faster. See dry scooping.
Is it the caffeine or something else?
Beta-alanine tingling and niacin flushing can feel alarming but are not cardiac effects. A true palpitation is a heartbeat you can feel thumping, skipping or racing. See why pre-workout makes your skin tingle.
What should you do when it happens?
- Stop exercising and sit down.
- Sip water and breathe slowly.
- Avoid more caffeine for the rest of the day.
- If symptoms settle within about an hour, lower the dose next time or skip the product.
How can you prevent it?
- Work out 3 mg/kg for your weight (210 mg at 70 kg) and stay at or below it.
- Choose a product that publishes caffeine. Biogen Premium states 150 mg; start with half a scoop of any new tub.
- Count all caffeine in the day.
- Switch to a stimulant-free option such as USN Qhush Hyperdrive Caffeine Free (R309.95–R349.99, October 2026), or take citrulline and beta-alanine on their own.
- Do not train fasted in the heat with a full scoop.
When should you see a doctor?
See a doctor if you have repeated palpitations, a heartbeat that stays fast or irregular, dizziness, fainting, chest pain or breathlessness. Get emergency help by calling 10177 or 112 for chest pain, collapse or a seizure. People with known heart rhythm problems, high blood pressure, anxiety disorders, thyroid disease or who take antidepressants or stimulant medicines should speak to their doctor before using pre-workout. A 2026 South African Medical Journal letter from UCT clinical pharmacologists raises concern about caffeine toxicity from these products; see is pre-workout safe.
Pregnant women should keep caffeine to 200 mg a day, and under-18s should avoid pre-workout altogether.
Products mentioned, with dated prices
| Product | Size | Price | R per 6 g | Sweeteners |
|---|---|---|---|---|
| USN Qhush Hyperdrive Caffeine Free 234 g | 234 g | R309.95-R349.99USN online shop, Oct 2026 | — | not stated |
| Biogen Premium Pre-Workout 600 g | 600 g | R399.99-R429.99Dis-Chem Living Fit, Oct 2026 | — | not stated |
| ATP Fitness Citrulline Malate | 250 g | R280ATP Fitness shop, Oct 2026 | R6.72 | None |
ATP Fitness is a commercial partner of Healthnews24 and its products are featured on this site. Rankings follow our published method, and every pick, including ATP Fitness, shows its price maths and trade-offs. Read our disclosure.
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Related questions
- How much caffeine is in pre-workout in South Africa?
- Is pre-workout safe? What do South African doctors say?
- Does pre-workout raise blood pressure?
- Why does pre-workout make your skin tingle?
- What is the best stimulant-free pre-workout in South Africa?
Sources
- Guest NS et al. (2021) ISSN position stand: caffeine and exercise performance. JISSN
- NutraIngredients (Apr 2015): EFSA adopts caffeine opinion
- Taylor, Tatz, Madikizela & Blockman (2026), Concerns regarding toxicity associated with caffeine-containing pre-workout supplements (SAMJ 116(6), correspondence; title only read)
- Maughan RJ et al. (2018) IOC consensus statement: dietary supplements and the high-performance athlete. BJSM 52:439
- EFSA (2015): Scientific opinion on the safety of caffeine, topic page
Educational information only, not medical advice. Speak to a doctor, pharmacist or registered dietitian before using supplements if you are pregnant or breastfeeding, under 18, taking medication, or living with kidney, liver or heart disease.
Cite this page: Healthnews24, “Why does pre-workout cause heart palpitations or anxiety?”, updated 27 October 2026, https://www.healthnews24.co.za/answers/pre-workout-heart-palpitations-anxiety/. Plain-text version: /answers/pre-workout-heart-palpitations-anxiety.md