To boost energy levels and performance during exercise, many people turn to pre-workout supplements.

These formulas generally consist of a flavored mixture of several ingredients, each with a specific role in improving performance.

Yet, some people experience side effects after taking them.

Here are 5 side effects of pre-workout supplements — plus some tips for how to avoid them.

1. May make you feel jittery

Caffeine is one of the primary ingredients in many pre-workout supplements.

This stimulant has been shown to increase muscle strength and output during exercise while reducing fatigue (1, 2, 3).

In theory, caffeine allows you to get more out of a given workout.

Nonetheless, caffeine has several potential side effects, especially if you consume too much. These include insomnia, nausea, increased heart rate, drowsiness, headaches, anxiety, and jitteriness or restlessness (4).

What’s more, many pre-workout supplements pack high amounts — up to 500 mg of caffeine per serving. Serving sizes typically range from 0.35–1 ounce (10–30 grams).

In comparison, 1 cup (240 ml) of coffee contains only 95 mg.

Ways to reduce side effects

Caffeine dosing is very individualized, as some people tolerate it better than others.

The best way to reduce side effects is to start with a small dose of a caffeinated pre-workout supplement, slowly increasing your dosage to see what you can tolerate.

Remember that it’s best to avoid caffeine for at least 6 hours before bed to help prevent sleeplessness (5).

Of course, you can also choose pre-workout supplements without any caffeine.

Summary You’ll find caffeine in most pre-workout supplements, but this stimulant can cause jitteriness, anxiety, and an increased heart rate. If you experience side effects, try a smaller dose to see how your body reacts.

2. May increase water retention

Another popular ingredient in many pre-workout formulas is creatine.

It has been shown to increase high-intensity exercise capacity and lean body mass gains from exercise (6).

While it’s most often part of a pre-workout supplement, creatine can also be taken on its own.

The main side effects associated with creatine are fairly mild but include water retention, bloating, weight gain, and digestive issues.

Ways to reduce side effects

Despite these side effects, creatine has been shown to be exceptionally safe (7, 8).

You can reduce any adverse symptoms by ensuring proper dosing.

Creatine is typically dosed with a loading phase of 4 scoops (20 grams) per day for at least 3 days, followed by a 3–5-gram daily maintenance dose.

This method provides rapid benefits — but has a higher potential to cause digestive issues and bloating (6).

Alternatively, you can take a single daily dose of 3–6 grams if you’re willing to wait for 3–4 weeks to experience benefits. This option is best if you want to avoid side effects like bloating, especially for those with a sensitive stomach (6).

Notably, it may be difficult to avoid moderate weight gain of 2–6 pounds (1–3 kg) while taking creatine. This is mainly due to increased water retention in your muscles (6).

Summary The easiest way to avoid mild side effects from creatine is to take smaller daily doses instead of doing a loading phase.

3. May trigger mild reactions

Two additional ingredients in many pre-workout supplements are beta alanine and niacin (vitamin B3).

Beta alanine is an amino acid that reduces acidity in your muscles during exercise, which may help you sustain your workout for slightly longer.

Dosed at 4–6 grams per day, it has been shown to increase exercise performance and reduce fatigue in high-intensity exercises lasting 1–4 minutes (9, 10).

Yet, this ingredient may cause paresthesia, a tingling sensation in your hands and feet. While it’s a harmless nervous system reaction, some people may find it uncomfortable (11).

Another ingredient with mild downsides is niacin, which is included in many pre-workout supplements for its skin-flushing effects. In high doses of 500 mg or more, it can trigger a blood rush to the surface of your skin, resulting in red patches (12).

While niacin also plays an important role in energy metabolism, supplementing with it likely doesn’t offer additional benefits if you consume a well-balanced diet (13).

Ways to reduce side effects

The most effective method to reduce the tingling associated with beta alanine is to divide the daily 4–6-gram dose into 2 separate doses of 2–3 grams each. Alternatively, you can buy sustained-release formulas that prevent this side effect (14).

Meanwhile, keeping your dose of niacin to less than 500 mg may prevent niacin flush. You can also purchase niacin-free products. Just be sure to check the ingredients on the label (15).

Summary Beta alanine and niacin are two common ingredients in pre-workout formulas that may cause tingling and skin flushing, respectively. You can prevent these side effects by dividing or reducing your doses — or selecting products without these compounds.

4. May cause digestive upset

Several ingredients in pre-workout formulas may cause digestive upset.

These include sodium bicarbonate, magnesium, creatine, and caffeine.

Sodium bicarbonate may cause problems when consumed at 91–227 mg per pound of body weight (200–500 mg per kg). However, most pre-workout supplements do not contain this much (16).

Magnesium, on the other hand, may have laxative effects — especially in the form of magnesium citrate. Thus, taking too much may cause diarrhea (17).

Interestingly, using too little water when mixing pre-workout supplements may likewise upset your digestion. Too concentrated a liquid could lead to diarrhea (18).

Ways to reduce side effects

Mixing your pre-workout supplement with 8–12 ounces (240–350 ml) of water can minimize side effects.

As it’s difficult to determine which ingredient is causing digestive issues, you may want to try different pre-workout formulas until you find one you can tolerate.

Summary Several ingredients in pre-workout supplements may trigger digestive issues in some people. Mixing them with enough water can alleviate these effects.

5. May cause headaches

Citrulline, which is added to some pre-workout supplements, is meant to increase blood flow to your muscles during exercise, resulting in enhanced muscle building.

This amino acid works by boosting nitric oxide levels in your blood (19).

The recommended dose for citrulline malate, a common form of this ingredient, is 6–8 grams — though many pre-workout supplements offer smaller amounts and may not provide the potential benefits.

Keep in mind that this increase in blood flow affects your brain as well as your muscles, leading some people to experience headaches and migraines. This is due to blood pressure changes in your brain’s small blood vessels (20).

Ways to reduce side effects

The most effective way to reduce headaches from citrulline is to decrease your dosage.

If you find that you still struggle with headaches, you may want to find a pre-workout supplement without this ingredient.

Summary Citrulline, a common ingredient in pre-workout formulas, may cause headaches by increasing blood flow in your body. Decreasing your dosage may minimize this effect.

Should you use pre-workout supplements?

You don’t need to take a supplement to benefit from exercise.

However, if you’ve trained consistently for at least six months, pre-workout supplements may help increase your exercise capacity (21, 22).

If you’re interested in trying a formula, look for a stamp from an independent lab that ensures quality. Testing companies included, USP, and NSF International.

In addition, it’s always recommended to check ingredient lists for anything you may react to. You may also want to avoid proprietary blends, as these conceal the specific amounts of each ingredient used.

Summary Pre-workout supplements may increase your exercise capacity if you maintain a wholesome workout regimen and diet, but they’re not necessary to attain good results.

The bottom line

Pre-workout formulas are popular in the fitness community due to their effects on energy levels and exercise performance.

However, you may experience side effects, including headaches, skin conditions, tingling, and stomach upset.

You can minimize many of these side effects by decreasing your dosage or avoiding supplements with particular ingredients.