Caffeine is the most widely-used stimulant in the world. It’s found in coffee, tea, soda, energy drinks, and energy shots, as well as some sports gels, dietary supplements, over-the-counter medications, and combat ration items (pudding, gum, and mints). In moderate doses, caffeine can boost both physical and mental performance. As with other stimulants, though, too much caffeine can have negative consequences, so it’s important to be aware of how much caffeine you’re consuming, and use it appropriately and strategically. Dietary supplements sometimes have significant amounts of caffeine, which adds to your daily intake, so pay special attention to what’s on the labels.

How much caffeine is safe?

For healthy adults, including women who are not pregnant or lactating, up to 400 mg per day of caffeine is considered safe. Less than that isn’t likely to lead to serious side effects. However, sensitivity to caffeine differs from person to person. Side effects include headaches, dizziness, nervousness, restlessness, and trouble sleeping. More serious side effects can occur with higher doses. In fact, 150–200 mg/kg bodyweight—or about 10–14 grams for the average person—can be fatal. This amount might seem difficult to achieve, but pure and highly concentrated caffeine are readily available and sold as dietary supplements, which the Food and Drug Administration (FDA) warns against because it’s up to you as the consumer to accurately measure out a serving. And, according to FDA, one teaspoon of pure powdered caffeine contains as much caffeine as 28 cups of coffee.

If I use caffeine for performance, how much should I use?

Caffeine can help improve some, but not all, measures of cognitive performance, such as vigilance, attention, and alertness, during long activities such as patrolling at night or when you are sleep deprived. For physical performance, caffeine works better for endurance rather than for short-term, high-intensity, or strength activities.

The exact amount of caffeine that can help performance varies among indviduals, and some respond better than others. In general, up to 200 mg (about the amount of caffeine in 8–12 oz of brewed coffee) at any one time is appropriate. Consume caffeine about 30–60 minutes before a workout, training session, work shift, or mission for best results, as it takes about an hour to reach peak blood levels. That also means you might need another dose of caffeine after 3–4 hours to help you stay alert or active for a long period of time. However, add up all the sources of caffeine in your diet and do not exceed 600 mg of caffeine per day (800 mg for sustained operations) to minimize risk of side effects.

How can I tell if my supplement contains caffeine?

If your supplement is marketed for weight loss, energy, or pre-workout, it probably contains caffeine. To see if your supplement contains caffeine, look at the Supplement Facts panel. Caffeine is often listed simply as “caffeine,” but various forms or terms include “caffeine anhydrous,” 1,3,7-trimethylxanthine, and others.

Other times the caffeine might be “hidden” in an ingredient. Sources of caffeine include:

  • Cocoa (cacao, Theobroma cacao)
  • Coffee or coffea
  • Green coffee bean
  • Guarana
  • Kola nut
  • Methylxanthine
  • Tea (Camellia sinesis)
  • Trimethylxanthine
  • Xanthine
  • Yerba maté

The total amount of caffeine might be listed on the Supplement Facts panel. If the caffeine is included in a “proprietary blend,” you might not be able to tell from looking at the Supplement Facts panel how much caffeine is in a serving. The amount of caffeine might be listed elsewhere on the container, so be sure to read the entire product label. Regardless, when looking at labels, look for the total amount of caffeine per serving in the product and factor it into your total daily caffeine intake.

What else should I know about caffeine?

While caffeine can improve how you perform, there are a few things you should keep in mind:

  • If you do choose to use caffeine, make sure you try it before an event or mission to assess your tolerability. Caffeine can provide some benefit, but it’s not a necessity.
  • More caffeine will not improve your performance, and the various negative side effects of higher doses might actually make it worse.
  • Try to avoid caffeine for at least 6 hours before bedtime to make sure it doesn't interfere with your sleep.
  • Caffeine can boost mental performance, but it’s not a substitute for sleep.
  • Be aware too of supplements containing caffeine along with other stimulants because there’s limited information about the safety of combining such ingredients.

For additional information about caffeine:

Updated 26 February 2019


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