Everything you need to know about caffeine—including how to quit

I’ll never know how much caffeine I consumed the night I drank nearly my weight in Typhoo tea, but considering I was awake for 24 hours, it was a significant amount. The tea was delicious, and my conversation with friends was engaging, both of whom conspired to see me down three cups before I realized what I’d done. A feeling of jitters followed; then a headache; then a racing heart; and finally, a full day and night of sleeplessness.

That may have been my lowest caffeine moment, but it wasn’t the only time I’ve overdone it. Like most adults, I consume caffeine daily, and I’ve sometimes paid a heavy price—especially when it comes to insomnia. So, what’s too much caffeine? How can you quit if you want to? And what’s the best time of day to stop drinking it if you don’t want to spend the night staring at the ceiling? Here’s what you need to know.

What are the effects of caffeine?

In the brain, caffeine blocks or inhibits the effect of adenosine, a DNA building block found in all cells in the body. Normally, adenosine is a central nervous system depressant, promoting sleep and inhibiting wakefulness. Caffeine begins its effect on adenosine relatively quickly; it is absorbed by the small intestine and peaks within about 30 minutes, depending on several factors, including the amount of food in the stomach.

Which beverages contain caffeine?

Caffeine is found in cups of coffee, and the amounts can be quite high. The FDA recommends limiting caffeine intake to 400 mg or less per day. One cup of coffee (8 ounces) contains about 100 mg, and with coffee shops like Starbucks selling single servings of up to 20 ounces, it’s easy to exceed this limit—especially if you start drinking coffee early in the day.

Tea, of course, also contains caffeine. An 8-ounce cup of black tea contains about 50 mg, while green tea contains about 30 mg. Cola contains 22 mg in an 8-ounce cup, and while this is significantly less than coffee, soft drinks are typically served in 12-ounce cans or 20-ounce bottles, so caffeine can add up here as well.

As for energy drinks, beware. A small (8.4-ounce) can of Red Bull contains 80 mg of caffeine, while a 2-ounce energy drink contains 215 mg, according to the Mayo Clinic. It’s difficult to predict how anyone will react to these caffeine doses, and the 400 mg limit is just a general guideline.

“There are individual differences in how caffeine is metabolized, so some people may experience unwanted side effects with even a smaller amount of caffeine,” says registered dietitian Maya Feller.

What are the side effects of caffeine?

Because caffeine is a stimulant, it can make it difficult to fall asleep and stay asleep. Other side effects include irritability, nervousness, excessive urination, headaches, and muscle tremors, says registered dietitian Mindy Harr, dean of the College of Health Professions at the New York Institute of Technology. “For people with a history of anxiety, depression, or mood disorders, consuming large amounts of caffeine can exacerbate feelings of restlessness,” adds Filler.

You may also experience caffeine withdrawal symptoms. These symptoms may mimic those of withdrawal from other mood-altering substances, including headaches, fatigue or drowsiness, mood swings, irritability, poor concentration, nausea, vomiting, or muscle aches and stiffness.

So, how do you safely quit caffeine?

For most people, caffeine isn’t harmful and may even have health benefits. According to the American Heart Association, regular coffee drinkers may have a lower risk of cancer and many other chronic diseases. Caffeine may also suppress appetite and reduce the risk of depression. But this mostly applies to people who consume caffeine in moderation. Others may experience irritability, insomnia, and other uncomfortable side effects of coffee. For them, abstaining—or at least cutting back—may be the best option.

It’s best to quit caffeine the same way you would quit any other medication: gradually. “I don’t recommend abrupt cessation, especially for regular caffeine users,” says Filler. Start by reducing your intake by 5% to 10% per day, drinking your caffeine earlier in the day. “Continue this for 3-4 days, then stop drinking the second drink until all the caffeine is consumed before noon,” limiting your daily intake to 400 mg. Continue this gradual detox regimen until you reach your desired level.

Cutting out caffeinated beverages has its downside. It can mean reducing your total daily fluid intake, and that can be detrimental to your health. According to the Mayo Clinic, men should drink about 15.5 cups, or 3.7 liters, of fluids per day, while women should consume 11.5 cups, or 2.7 liters. Therefore, Haar recommends replacing every caffeinated beverage with water or a decaf beverage.

When should you stop drinking caffeine during the day?

Fieler recommends that people who work a 9-to-5 schedule limit their caffeine intake to the hours before noon. If you work an irregular shift or night shift, also stop drinking caffeine 10 or 11 hours before bedtime. The Sleep Foundation gives you more leeway, suggesting you stop consuming caffeine at least eight hours before bedtime. However, there are differences from person to person.

“Besides general differences in metabolism between people, obesity, smoking, oral contraceptive use, altitude, and pregnancy can affect how long it takes for caffeine to completely leave your system,” says Har. “You should monitor your caffeine intake and how easily you fall asleep.”