Caffeine and Energy Drinks: Benefits, Limits and Risks

What caffeine does and does not do

Caffeine is a stimulant found in coffee, tea, chocolate, soft drinks, energy drinks and some supplements and medicines. [1] It can make you feel more alert, but MedlinePlus states that stimulants, including caffeine, are not effective treatments for fatigue and can make the problem worse when they are stopped. [2] Caffeine can also keep you from a good night's sleep, which can feed tomorrow's tiredness. [3]

How much is in common drinks

The FDA gives typical caffeine in 12-fluid-ounce drinks: [1]

Amounts vary by product and container size. Decaffeinated coffee still has some caffeine (2 to 15 mg in an 8-ounce cup). [1] Energy drinks generally have 54 to 328 mg per 16 fluid ounces, and may include other caffeine sources such as guarana, which should be counted on the label. [1] Caffeine added to a product behaves like the caffeine in coffee or tea. [1] See Coffee, Black tea and Yerba mate.

Established guidance on amounts

For most adults, the FDA has cited 400 mg a day (about two to three 12-ounce cups of coffee) as an amount not generally associated with negative effects. It stresses wide variation in sensitivity and how fast people clear caffeine, and says certain conditions and medications make people more sensitive. [1] If you are pregnant, trying to become pregnant, or breastfeeding, the FDA recommends talking to your provider about limiting caffeine. [1] UK NHS advice is not to exceed 200 mg a day in pregnancy. [4] This is not a personal target. Your own limit may be lower.

Timing and sleep

Established. In a home study, 400 mg of caffeine taken 0, 3 or 6 hours before habitual bedtime each disturbed sleep compared with placebo, and the authors concluded caffeine should be avoided for at least 6 hours before bed. [5] Details: Caffeine, alcohol, nicotine and sleep.

Performance

Established for exercise performance. An umbrella review of 21 meta-analyses found caffeine was ergogenic (performance-enhancing) for aerobic endurance, muscle strength, muscle endurance, power and speed, with moderate quality evidence, mostly from young men. [6] This is about sports tasks, not about curing everyday tiredness.

Energy drinks: extra concerns

• Cardiovascular effects. A 2025 systematic review of 37 studies (1,597 participants, average age 22.6) reported increased heart rate, blood pressure and QTc interval prolongation (a change on heart tracings) across many studies, and called for research on at-risk groups and long-term effects. [7]
• Children and teens. Medical experts, including the American Academy of Pediatrics, advise against energy drinks for children and teens because of sugar and caffeine. Too much can cause fast heart rate, palpitations, high blood pressure, anxiety and sleep, digestive and dehydration problems. [1]
• Stacking. Caffeine appears in bars, gum, supplements and medicines, so totals add up. [1] See Energy supplements compared.

Signs you are having too much

The FDA lists increased heart rate, palpitations, high blood pressure, insomnia, anxiety, jitters, upset stomach, nausea and headache. [1] Talk with a health professional if you have these. [1]

The "crash" and cutting back

If you drink caffeine every day and want to cut back, the FDA advises doing so gradually. Withdrawal is not considered dangerous but can be unpleasant. [1]

Pure and powdered caffeine

The FDA estimates toxic effects such as seizures can occur with rapid consumption of about 1,200 mg of caffeine, less than half a teaspoon of pure caffeine, and says pure and highly concentrated products can cause death. [1] The FDA notes such products were sold in bulk packaging that required buyers to measure a safe serving from what can be a toxic or even lethal amount. [1] For severe symptoms in the US call 911; for poisoning advice call Poison Help at 1-800-222-1222 (see Poisoning: what to do first and Poison Help by country). In other countries, use your local emergency number.

Alternatives

Water, rest, light activity and sleep are the foundations. See Everyday habits for energy. Decaf is not caffeine-free. [1]

When to get help

Talk with a health professional if caffeine gives you palpitations, a fast heart rate, anxiety or sleep trouble. [1] See Fatigue: when to get help and How interactions work.