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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Minding Your Mind Minding Your Mind

Caffeine: Performance, Addiction and Myth

November 16, 2013

By Michael Craig Miller M.D.

Harvard Medical School

Passionate about your coffee? Me, too.

In fact, I should confess I'm a coffee snob. I've been buying java from the same purveyor for more than 25 years and people around my office identify me as a booster of the brand. I have my own small coffee machine in my office, which I put to work ritualistically every morning on arriving. You probably have your own ritual. Maybe you prefer tea, or — like someone I know — maybe you have a hoard of diet cola in a small refrigerator under your desk. You pursue your habit not just because you like the taste, but also because the active ingredient, caffeine, has you hooked.

Caffeine is the most widely used psychoactive drug in the world. Almost 9 out of 10 Americans take it regularly in some form, usually in a drink, but sometimes as a pill (No-Doz and others). The average daily consumption is about 300 milligrams, which is like drinking three cups of coffee. Now that you understand why coffee is such big business, let's see if it is good business for you.

Efficiency in a Cup?

Caffeine is so popular because of its stimulant effects. We believe it will help us work more quickly and efficiently. We also use coffee to stay alert and awake, even as the day is fading. It does not, however, work as well as we think it does.

In several studies comparing how people feel on and off caffeine, caffeine users report feeling more alert and more attentive. They have faster reactions, learn new information more quickly, and persist longer when carrying out a task. Their mood is better too. Scientists have shown that caffeine has a boosting effect on those chemical messengers in the brain that help us pay attention, code information, and react to the world around us.

This sounds like great news, but the research may be misleading. Caffeine studies are notoriously difficult to do. The most reliable way to judge a drug's effects is to compare a group taking the drug to a matched group taking a placebo. But so many people use caffeine, it's almost impossible to find non-users. Also, those who do abstain are such a small group that scientists think the way they experience caffeine is biologically different from everyone else. For example, they may be people who find the substance unpleasant. To do a good study, you need to find — or create — habitual caffeine users who are not using. Even when researchers have been careful to do this, their studies rarely last long enough to show us the upshot of chronic use.

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Is the Performance Boost a Myth?

Our intuitions about caffeine may be wrong. Researchers now think caffeine may not actually enhance our abilities. Rather, caffeine may just offset the problems caused by caffeine withdrawal. That is, when we drink our morning cup, it just gets us back to where we started.

Non-consumers actually start out more alert than habitual consumers do before their first morning cup. For those non-consumers (or people who have abstained for a week), the kick of the first caffeine dose is noticeable and they do better on intellectual testing, but they quickly become tolerant to the stimulation.

Once people get in the caffeine habit, it's no use increasing intake — it only gives them the jitters and messes up their performance.

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Caffeine Withdrawal: A Daily Process

Caffeine is quickly and completely absorbed through the digestive tract. Blood levels peak in half an hour or so, and half of the caffeine in your body is excreted within four to six hours. Withdrawal symptoms can start as soon as six hours after stopping use, though 12 to 24 hours is more common. Withdrawal symptoms are very common on waking in the morning. Were you to stop ingesting caffeine, withdrawal symptoms probably would last at least a day or two; they could go on for up to two weeks.

The most common withdrawal symptom is headache — about half of caffeine users get them. Fatigue, low energy, decreased alertness, irritability or depressed mood are also common. Attention and motor performance get worse. About 10% of withdrawing caffeine users describe severe distress or find it very hard to function.

A friend of mine told me a family member would regularly play a trick on her, substituting decaf for caffeinated coffee without her knowing it. The trickster was trying to prove that withdrawal symptoms were nothing more than expectations fulfilled. Controlled experiments have proven that theory wrong. Withdrawal symptoms have their basis in pharmacology. The more caffeine you use, the worse the withdrawal symptoms. But the cure is quick — a drink of coffee or tea can eliminate symptoms within an hour.

So what we experience as a performance enhancement is probably just a daily cycle of withdrawal and relief. That first cup tugs you back up to the starting line rather than giving you a head start.

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Will It at Least Keep Me Awake?

Maybe caffeine will keep you awake, but unfortunately it may do so only when you want to sleep. If you have been getting a normal amount of sleep, and you take more caffeine than you are used to, especially in the afternoon or evening, you are likely to have trouble falling asleep. But if you are sleep-deprived, caffeine probably will not be enough to combat your drowsiness. In one study comparing people who were sleep-deprived to those who were not, caffeine did not improve performance for anyone.

So the research does not support your using caffeine to make up for a sleep deficit. It is not a dependable tool for students trying to study through the night. And it is completely untrustworthy if you are driving a car or truck. The proper antidote for sleep deprivation is sleep.

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Caffeine for Pleasure, Not for Performance

We should accept caffeine's limitations. It probably won't enhance your performance and it can't compensate you in the morning if it spoiled your good night's sleep.

Happily, it will reliably relieve symptoms of caffeine withdrawal that may be dragging you down. If you take pleasure in your daily coffee, tea or cola ritual, there is no reason to stop enjoying it. But remember, your preferences and your ritual may have been shaped by those withdrawal symptoms that you work to avoid every day.

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Michael Craig Miller, M.D., is the Editor in Chief of the Harvard Mental Health Letter. He is also associate physician at Beth Israel Deaconess Medical Center and assistant professor at Harvard Medical School. He has been practicing psychiatry for over 25 years at Beth Israel Deaconess Medical Center. He teaches in the Harvard Longwood Psychiatry Residency Program.

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