The FDA's published guidance puts caffeine intake for most healthy adults at up to 400 milligrams a day — roughly four to five eight-ounce cups of coffee — an amount the agency states is not generally associated with dangerous, negative effects. A single eight-ounce cup of brewed coffee delivers about 80 to 100 milligrams, per FDA figures, a 12-ounce cola about 30 to 40, and an eight-ounce energy drink 40 to 250. The agency's rules go further for pregnancy, where it advises pregnant women to limit or skip caffeine, and for adolescents, where it recommends smaller intakes.
This site publishes information, not medical advice. The 400-milligram figure is a federal population reference, not a personal prescription: sensitivity varies widely, and people with heart conditions, anxiety disorders, sleep disorders, or pregnancy should set their own limit with a clinician.
Where does the 400 mg figure come from?
The FDA cites the amount in its consumer guidance, Spilling the Beans: How Much Caffeine is Too Much?, first issued in 2013 and updated since, including a 2023 revision to its broader caffeine materials. The figure aligns with international assessments — Health Canada's 2012 scientific review arrived at a comparable 400-milligram ceiling for healthy adults — and the agency frames it as the level at which dangerous effects are not generally observed, not a threshold below which caffeine is harmless. The FDA has also moved on the supply side: dietary supplements with added caffeine have drawn the agency's attention, including warning letters over concentrated pure caffeine powders after deaths were reported, and in 2023 the FDA stated it was exploring whether to restrict added caffeine in supplements.
How much caffeine is in common drinks?
| Item | Caffeine (mg) | Source |
|---|---|---|
| Brewed coffee, 8 oz | 80–100 | FDA |
| Espresso, 1 oz | About 64 | USDA FoodData Central |
| Brewed black tea, 8 oz | 30–50 | FDA |
| Cola, 12 oz | 30–40 | FDA |
| Energy drink, 8 oz | 40–250 | FDA |
| Decaf coffee, 8 oz | 2–15 | FDA |
The energy-drink range is the widest because manufacturers list amounts that vary tenfold across brands and serving sizes, and the FDA requires caffeine listing only as an ingredient, not a quantified amount, on most labels.
What are the warning signs of too much?
The FDA's consumer materials list insomnia, jitteriness, anxiety, fast heart rate, upset stomach, nausea, and headache among effects of excessive intake, and note that about 1,200 milligrams in a short period can produce toxicity symptoms including seizures — a level reachable with concentrated caffeine products, not with brewed coffee. The safety question the agency has pursued hardest involves concentrated powders and liquids sold as dietary supplements, where a single tablespoon of powder can approach a lethal dose; the FDA urged consumers to avoid pure caffeine products entirely in 2018.
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What about caffeine for shift workers?
Caffeine genuinely improves alertness, which is why NIOSH materials acknowledge it among fatigue-countermeasure options for night workers. The trade-off documented in sleep research is timing: caffeine's half-life averages about five hours in healthy adults, per pharmacology reviews, so a 6-ounce cup at 4 a.m. still carries roughly half its dose at 9 a.m., into the daytime sleep window. Night workers using caffeine strategically take it early in the shift and cut off six or more hours before intended sleep — a rule of thumb drawn from pharmacokinetics, not an official standard.
Does the safe amount differ for some people?
Yes, and the FDA says so directly. Its guidance advises pregnant women to limit or avoid caffeine, citing slower clearance during pregnancy; recommends smaller amounts for adolescents; and notes individual variation in sensitivity driven by genetics, medications that interact with caffeine metabolism, and underlying conditions. People with palpitations, reflux, chronic insomnia, or anxiety that tracks coffee intake are describing individual tolerances below the population figure — a clinician can weigh those against any medications in play rather than against the FDA average.
What about withdrawal and dependence?
The FDA's materials acknowledge that regular users who stop abruptly can expect headache, fatigue, and irritability lasting days, which pharmacology literature describes as physical dependence in the ordinary sense — though the agency has never classified caffeine among controlled substances and sees no population-level reason to. The practical consequence shows up in hospitals and police stations, not clinics: workers who rely on coffee to manufacture alertness on long shifts experience a trough when access drops. Tapering over a week or two blunts the withdrawal symptoms, per standard clinical references, and switching part of daily intake to decaf — which still carries 2 to 15 milligrams per cup, per FDA figures — preserves the ritual while cutting the dose.
How should a reader use the FDA number?
As an anchor with named provenance: 400 milligrams, issued by the agency that regulates caffeine-containing products, aligned with Health Canada's 2012 assessment and framed as a ceiling for danger rather than an optimum. Anyone tracking a personal total will find the table above does most of the work — coffee dominates, tea and cola contribute modestly, energy drinks vary by label, and chocolate and medications add small amounts the FDA notes in passing. What the number cannot settle is individual tolerance, medication interactions, or symptoms that persist below the threshold; those are clinician conversations, and the FDA's own guidance points consumers with concerns in exactly that direction.