What does pre-workout do?

The main ingredients and what they do

Because beta-alanine and creatine depend on daily use, the timing of a single serving matters less than taking them consistently. Caffeine is the ingredient you'll feel on the day.

Side effects to expect

• Tingling (paresthesia): from beta-alanine, usually on the face, neck and backs of the hands. It's dose-related, fades within about 60 to 90 minutes, and hasn't been linked to harm.
• Jitters, fast heartbeat, upset stomach, headache and anxiety: signs of too much caffeine.
• Poor sleep: caffeine can delay sleep and reduce deep sleep, so evening workouts and pre-workout don't mix well.
• Weight gain: creatine draws a little water into muscle, which can add a small amount of weight early on.

How much caffeine is too much?

FDA cites 400 milligrams a day for most healthy adults, about two to three 12-ounce cups of coffee, as an amount not generally linked to negative effects. People vary a lot in sensitivity. Add up the caffeine in your pre-workout, coffee, tea, soda and energy drinks.

• Pregnant or breastfeeding people, people with heart conditions or high blood pressure, and anyone on certain medicines should ask a clinician first.
• The American Academy of Pediatrics advises against energy drinks for children and teens.
• Avoid pure powdered caffeine. FDA says one teaspoon has as much caffeine as 28 cups of coffee, and these products have been linked to deaths.

Stimulants and claims to avoid

FDA says DMAA, an amphetamine-like stimulant sometimes found in sports and weight-loss products, is not a legal dietary ingredient. It can raise blood pressure and may cause heart attack, irregular heartbeat and seizures, with greater risk when combined with caffeine. On labels it may appear as 1,3-dimethylamylamine, methylhexanamine, geranamine, or geranium extract.

Dietary supplements don't need FDA approval before they're sold, so choose products with a third-party testing seal and a clear amount for each ingredient rather than a "proprietary blend."

Stop and get medical care right away for chest pain or tightness, a racing or irregular heartbeat, fainting, severe headache, shortness of breath or a seizure after using a pre-workout.

A free Gabriel account pays cost-plus prices on supplements, and Gabriel Core and Plus members pay lower member prices. See creatine monohydrate and beta-alanine.