Why does pre-workout cause heart palpitations or anxiety?

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?

1. Stop exercising and sit down.
2. Sip water and breathe slowly.
3. Avoid more caffeine for the rest of the day.
4. 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.

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