Reference · FDA, NIH & USDA

Coffee and caffeine: the facts

Caffeine is the reason many of us drink coffee at all. Here is what the U.S. Food and Drug Administration (FDA), the National Library of Medicine’s MedlinePlus and the U.S. Department of Agriculture say about how much is in a cup, how much is too much, and who should be more careful.

The headline number: 400 mg a day

For healthy adults, the FDA cites 400 milligrams a day as an amount not generally associated with negative effects — about two to three 12-ounce cups of coffee. MedlinePlus gives the same figure. Both stress that people vary widely in how sensitive they are to caffeine and how quickly they clear it, so “too much” differs from person to person.

How much caffeine is in your drink?

Two things stand out. First, coffee varies enormously: a 12-ounce cup might carry 113 mg or more than twice that, depending on beans, strength and brew method. Second, decaf isn’t caffeine-free — the FDA puts it at about 2–15 mg per 8-ounce cup.

For specific products, the FDA suggests contacting the manufacturer or checking USDA FoodData Central, the U.S. Department of Agriculture’s food-composition database, managed by the Agricultural Research Service and hosted by the National Agricultural Library. Packaged foods must list added caffeine in their ingredients, but caffeine that occurs naturally in an ingredient (such as chocolate) may not be listed separately, and restaurants aren’t required to disclose caffeine content — so ask.

What changes the caffeine in your cup?

• The species. Robusta beans contain about 2.7% caffeine versus about 1.5% for arabica, so robusta-heavy blends and instant coffee can be stronger.
• Not really the roast. Caffeine survives typical roasting temperatures. Dark roast is not “stronger” in caffeine; by the scoop, light roast has slightly more because it is denser. See beans and roast levels.
• How much coffee you use. A stronger ratio puts more coffee — and more caffeine — in the cup. Our brewing page explains ratios.
• Cup size. Many “cups” are well over the 8 ounces used in reference figures.

How caffeine acts in the body

According to MedlinePlus, caffeine stimulates the central nervous system, which can make you more alert. It also acts as a diuretic, increases stomach acid (which can cause upset stomach or heartburn), may interfere with calcium absorption, and raises blood pressure. Blood levels peak within about an hour, and effects can last four to six hours — worth remembering when you reach for an afternoon cup.

Signs of too much

The FDA and MedlinePlus list similar effects of excess caffeine: fast heart rate or palpitations, higher blood pressure, insomnia, anxiety and jitters, restlessness or shakiness, upset stomach or nausea, headache, dizziness and dehydration. If you notice these, the FDA suggests talking with a health care professional.

Stopping suddenly after regular use can cause withdrawal — headaches, drowsiness, irritability, nausea and trouble concentrating — which usually passes within a few days, MedlinePlus says. Cutting back gradually is gentler.

Who should be more careful

• Pregnant people, those trying to conceive, and those breastfeeding should ask their provider whether to limit caffeine (FDA).
• Children and teens should consume less than adults; the Dietary Guidelines for Americans advise no caffeinated drinks for children under 2, and the American Academy of Pediatrics advises against energy drinks for children (FDA).
• People with certain conditions — sleep disorders, migraines, anxiety, GERD or ulcers, heart arrhythmia or high blood pressure — and people taking stimulants, some antibiotics, asthma or heart medicines should check with a provider (MedlinePlus).

Never use pure caffeine powder

Pure and highly concentrated caffeine products are a different matter from coffee. The FDA estimates that toxic effects, including seizures, can follow rapid intake of about 1,200 mg — less than half a teaspoon of pure caffeine — and warns these products can cause serious harm, including death. Brewed coffee is a far safer way to get your caffeine.