Many of us can’t imagine starting the day without our favorite caffeinated beverage. But you may wonder, how much caffeine is too much in one day? And, is caffeine withdrawal a real thing? Also, should you be concerned about caffeine side effects? To find out, we spoke with Laura Juliano, PhD, director of The Behavioral Pharmacology and Health Promotion Laboratory at American University in Washington, DC.
Caffeine’s effects
Caffeine is a psychoactive drug that blocks a receptor in the brain reserved for adenosine, a neurotransmitter that causes sleepiness. When that receptor is blocked, we experience the desirable effects of alertness, sociability and improved mood.
How long does caffeine last in the brain?
These effects typically peak within 30 to 45 minutes of consuming a caffeinated food or beverage. How fast we metabolize caffeine varies greatly, although the average half-life is about four to six hours. That means about half of the caffeine you consumed will remain in your system for about five hours after you have had it…after 10 hours, about one-quarter of it.
How much caffeine is too much?
Most people should limit their caffeine consumption to no more than 400 mg per day. Too much caffeine can cause anxiety and insomnia. Very high doses could cause caffeine intoxication, which is not typically life-threatening but can be quite unpleasant, causing dizziness, sweating, jitteriness, nausea, lightheadedness and rapid heartbeat.
How much caffeine is in coffee?
Caffeine exposure is difficult to measure because of the variety of forms in which we consume it…and the variable amounts within each form. Depending on how it’s made, one 16-ounce cup of coffee could have anywhere from 140 mg to 310 mg of caffeine. One shot of espresso in a latte might have as little as 60 mg to 80 mg. Caffeine content in soft drinks is “generally recognized as safe” (GRAS) to just about 70 mg per 12-ounce bottle, meaning that at this level no safety test is required. Energy drinks frequently contain 200 mg or more. To find out the caffeine content in what you are consuming, read the label or visit the Caffeine Calculator at CaffeineInformer.com.
What about caffeine withdrawal?
Because caffeine is found in so many things, it’s easy to imagine that it’s not a “real” drug—but it does cause physical dependence. It usually takes one to three weeks for withdrawal symptoms to resolve. The primary withdrawal symptoms are fatigue and headache, which peaks on the second or third day after you’ve stopped having caffeine.
To quit or cut back on your caffeine intake: You could try going cold turkey or taper off by replacing half your daily intake with a non-caffeinated substitute every week for about four weeks…and then after the four weeks, eliminate caffeine entirely. If you want to take a headache medicine to help you cope, check to make sure it doesn’t contain caffeine.
Special considerations: Oral contraceptives slow caffeine metabolism, which can cause people to feel more jittery when they consume it. Tobacco smokers have the opposite problem, with caffeine metabolism twice as fast as that of non-smokers, so they may feel caffeine’s effects less strongly and consume more. Pregnant women should limit caffeine intake to no more than 200 mg per day because caffeine metabolism slows down during the third trimester. Women trying to conceive should also try to consume less than 200 mg per day. And children and adolescents should limit daily caffeine to 2.5 mg per kilogram of bodyweight.
