Quick answer: The most common pre-workout side effects are jitters, a racing heart, poor sleep, tingling skin, headaches and an upset stomach. Most come from caffeine or beta-alanine. You can usually avoid them by starting with half a serving, keeping your total caffeine for the day under about 400mg, not taking pre-workout within 6 hours of bedtime, and drinking enough water.
Pre-workout supplements are designed to make you feel more alert and focused before training. The same ingredients that create that effect can cause side effects, especially if you are new to stimulants, take a full scoop on an empty stomach or also drink tea, coffee or energy drinks. Here is what causes each side effect and what to do about it.
Common pre-workout side effects at a glance
| Side effect | Usual cause | How to avoid it |
|---|---|---|
| Jitters, anxiety, racing heart | Too much caffeine for your tolerance | Start with half a serving; count all caffeine sources |
| Tingling or itchy skin | Beta-alanine (and sometimes niacin) | Split the dose or take a smaller serving; it is harmless |
| Trouble sleeping | Caffeine taken too late | No pre-workout within about 6 hours of bedtime |
| Headache | Caffeine, dehydration or the crash afterwards | Drink water; lower the dose |
| Nausea or loose stools | Strong formula on an empty stomach, too little water | Mix with enough water; eat a light snack first |
| Energy crash later | Caffeine wearing off | Use a smaller dose; do not stack with other stimulants |
1. Jitters, anxiety and a fast heartbeat
Caffeine is the main active ingredient in most pre-workouts. Health authorities such as the US FDA consider up to about 400mg of caffeine a day generally safe for healthy adults, and the European Food Safety Authority considers single doses of up to about 200mg unlikely to cause concern. A single pre-workout serving can contain 150–300mg. Denzour's Bee HP and Den Roar list 250mg of caffeine per serving, so tea, coffee and energy drinks on the same day add up quickly.
What to do: start with half a scoop, avoid other caffeine on training days and never take two servings to "push through" a session.
2. Tingling or itchy skin
The pins-and-needles feeling on your face, neck or hands is called paraesthesia. It is caused by beta-alanine and is harmless and temporary, usually fading within 60–90 minutes. Both Bee HP and Den Roar list 4500mg of beta-alanine per serving, so tingling is expected for many people. Read more in why pre-workout makes you tingle.
What to do: if you dislike the feeling, use a smaller serving. Beta-alanine works by building up in muscle over weeks, so smaller doses still work.
3. Trouble sleeping
Caffeine has a half-life of around 5 hours in most adults, meaning half of it is still in your body 5 hours later. An evening pre-workout can easily cut into sleep, and poor sleep hurts recovery more than the pre-workout helps.
What to do: avoid pre-workout within about 6 hours of bedtime. If you train late, use a stimulant-free option such as L-citrulline or simply train without one.
4. Headaches
Headaches can come from too much caffeine, not drinking enough water or the drop in caffeine a few hours later. Regular heavy users can also get withdrawal headaches on days they skip it.
What to do: drink water before and during training, use the smallest dose that works and take regular breaks from stimulants.
5. Nausea, bloating or loose stools
A concentrated scoop in very little water, taken on an empty stomach, can upset digestion. Some sweeteners and magnesium-containing ingredients also affect sensitive stomachs.
What to do: mix with the amount of water on the label, sip rather than gulp, and have a light snack 30–60 minutes before.
6. The energy crash
When caffeine wears off, some people feel tired or low a few hours later. The bigger the dose, the bigger the crash tends to be.
What to do: lower the dose and make sure you have eaten properly that day.
How to use pre-workout safely
- Start with half a serving to test your tolerance.
- Take it 20–30 minutes before training. See how long pre-workout takes to kick in.
- Count all caffeine sources in your day, including tea, coffee and fat burners.
- Do not combine two stimulant products, such as a pre-workout and a fat burner.
- Take a break of 1–2 weeks every couple of months so your tolerance does not keep rising.
Who should not use pre-workout
Pre-workout is not suitable for people under 18, pregnant or breastfeeding women, or anyone sensitive to caffeine. Speak to your doctor first if you have high blood pressure, a heart condition, anxiety, a thyroid condition or take regular medication.
Choose the right pre-workout
Check caffeine per serving and the full ingredient list before you buy. Our guide to pre-workout ingredients explains what each one does, and you can compare options in the pre-workout collection. New to it? Start with pre-workout for beginners.
Frequently asked questions
Is pre-workout bad for you?
For healthy adults who use it as directed and keep total caffeine within safe limits, pre-workout is generally well tolerated. Problems usually come from high doses, late-evening use or mixing several stimulants.
Why does pre-workout make me itchy?
That is beta-alanine. The tingling is harmless and fades within about 60–90 minutes.
Can I take pre-workout every day?
You can on training days, but regular breaks help keep your caffeine tolerance from climbing.
Can pre-workout raise blood pressure?
Caffeine can cause a short rise in blood pressure. If you have high blood pressure or a heart condition, speak to your doctor before using any pre-workout.
This article is for general information and is not medical advice. Follow the directions and warnings on your product label.
