You are not hungry, so lunch has turned into a fourth coffee and the one real meal of the day happens in the evening. Your hands are unsteady by the afternoon, your stomach is unsettled, and you lie awake long after you meant to be asleep, working out whether the medical weight care you are on is doing this to you.
Caffeine has a daily figure, a table that turns mugs into milligrams, and a list of effects that overlaps almost word for word with what you are describing. One ordinary day, added up honestly, tells you whether the coffee is carrying any of it — and it is the one thing in your week you can move without asking anyone's permission.
FDA cites, for most adults, an amount not generally associated with dangerous negative effects: 400 milligrams a day — that's about two to three 12-fluid-ounce cups of coffee. Five mugs of brewed coffee are past that at any strength, and how far past depends on the pot rather than the count. Jitters, an upset stomach, nausea, headache, anxiety, palpitations and broken sleep are all on FDA's list of what too much caffeine produces, and headache and nausea appear again on the list for stopping suddenly, so the direction you move matters as much as the amount.
The daily figure, and adding up your own day
Your day is counted in milligrams rather than in mugs, and one mug covers a wide range: a 12-fluid-ounce serving of brewed coffee carries 113 to 247 milligrams, so five of them clear the daily figure even at the weakest end of that range, and the strength of the pot decides how far past it rather than whether.
| 12 fluid ounces of | Caffeine |
|---|---|
| Brewed coffee | 113 to 247 mg |
| Energy drink | 41 to 246 mg |
| Black tea | 71 mg |
| Green tea | 37 mg |
| Soft drink | 23 to 83 mg |
Those ranges are per serving, and the figure they add up to is a whole-day figure. The tea at your desk and the soft drink with the evening meal go into the same total as the coffee. Nothing on that table covers espresso or a coffee shop's specialty drinks, so those are the ones to look up rather than estimate.
Going past the daily figure and reaching a dangerous amount are a long way apart. Toxic effects, like seizures, can be observed with rapid consumption of around 1,200 milligrams of caffeine — three times the 400 for an ordinary day, and taken quickly rather than spread across one.
Which symptoms sit on two lists at once
Your shakiness, your unsettled stomach and your open eyes at night are all on one list, and two of them are on a second list as well. Too much caffeine produces increased heart rate, heart palpitations, high blood pressure, insomnia or sleep disruptions, anxiety, jitters, upset stomach, nausea, and headache. Stopping abruptly after a regular habit produces headaches, drowsiness, irritability, nausea, trouble concentrating. Headache and nausea are on both, so neither of those two tells you which way you are moving.
Timing separates them, and you can check timing. Caffeine reaches its peak level in your blood within an hour of drinking it and can go on being felt for four to six hours, so a cup taken late in the working day is still doing something at bedtime. Withdrawal runs the other way, arriving after the intake falls rather than while it is high.
What to do about one meal a day is the other half of your week, and eating enough when you are not hungry at all is where that gets decided.
Why a powder is a different kind of product
One teaspoon of pure caffeine powder can contain the same amount of caffeine as 28 cups of coffee, which puts it and the liquid concentrates in a different category from anything you would pour into a mug. The difference between a safe amount and a toxic or life-threatening amount of caffeine in these highly concentrated products is very small.
Measuring is the step that fails at home. Volume measures such as teaspoons are not precise enough to calculate how many milligrams of caffeine are in the recommended serving size, so a person scooping at home has no way to land inside a window that narrow. FDA records that these products have contributed to at least two deaths in the United States and names rapid or dangerously erratic heartbeat, seizures and death among their effects.
Caffeine bought as a drink is limited by how much liquid a person will swallow in an afternoon. Caffeine bought as a powder is limited by a measuring spoon, and the spoon is not accurate enough to be a limit.
Adding up a day, and easing the total down
- Write down everything with caffeine in it for one ordinary day — coffee, tea, soft drinks, energy drinks — recording the size of each serving rather than the count.
- Convert that day with the table above and compare the total against 400 milligrams. Look up the coffee shop drinks instead of guessing them.
- Move the last caffeine of the day earlier before you touch the total, since the effect can run four to six hours. Change one thing at a time, or two changes leave you with no way to tell which did what.
- Come down gradually rather than stopping outright, because caffeine withdrawal brings its own headache and nausea and will look exactly like the thing you are trying to identify.
- Leave the powders and the liquid concentrates where they are. No kitchen measure gets you a safe amount of them.
- If you are pregnant, trying to become pregnant or breastfeeding, or you take anything regularly, talk to your health care provider about how much caffeine is right for you.
The shakiness, the unsettled stomach and the sleepless hours sit on one list together, and moving the caffeine while leaving the rest of your week alone is how you find out whether that list is yours. Nobody measured the pot in your kitchen, so the ranges above tell you the range you are in rather than the number you drank, which is an argument for running the week instead of doing arithmetic in your head. Whichever way it comes out, you end up with an answer nobody else has to give you.
