Q: What are caffeine’s psychological benefits and risks?
A:Caffeine is the most widely used psychoactive drug in the world. Up to 90 percent of Americans take it regularly, usually in the form of coffee, tea or soft drinks, sometimes in a tablet (No-Doz and others). The average daily dose, 300 mg, is the equivalent of three cups of coffee. No wonder selling expensive caffeinated drinks is good business.
The best way to determine the risks and benefits of a drug is to give the drug or a placebo to matched groups of people who have never been exposed to the drug. But it’s hard to find people who don’t use caffeine, and the small minority who don’t may abstain because they are physiologically different from others, finding caffeine unpleasant rather than pleasurable. Another problem is that most controlled studies don’t last long enough to reveal the effects of chronic use. Researchers are more interested in habitual users.
One of the more important questions raised by research is whether caffeine offers a true benefit (improved alertness and sustained attention, for example) or merely wards off the symptoms of caffeine withdrawal. Basic pharmacology is one guide here. Eat or drink substances containing caffeine, and it will be quickly and completely absorbed. Blood levels peak in well under an hour, and 50 percent of ingested caffeine leaves the body within four to six hours.
Withdrawal symptoms generally begin 12 to 24 hours after stopping use but can appear within 6 hours. So it’s not unusual to notice the symptoms in the morning after drinking coffee the previous day. On average, withdrawal symptoms last one or two days, but they can continue for as long as two weeks.
Headache is the most common withdrawal symptom, experienced by up to 50 percent of caffeine users. Other symptoms are fatigue, low energy, decreased alertness and depressed or irritable mood. Intellectual performance, vigilance and psychomotor speed decline. About one in 10 withdrawing caffeine users suffers significant distress or impairment.
Studies confirm that these symptoms have a pharmacological basis; they aren’t just a result of people’s expectations. The more caffeine you ingest, the more uncomfortable the withdrawal symptoms. Have a drink of coffee or tea, and the symptoms will go away within an hour.
The daily cycle of withdrawal and relief is so common that many experts question whether caffeine’s stimulant properties yield any net benefit at all. Tolerance to the stimulant effect develops rapidly. Nonconsumers (or consumers who’ve abstained for a week) say they feel more alert after consuming caffeine, but objective tests show no improvement in their performance. And nonconsumers start out more alert and at ease than habitual consumers after a night of abstinence.
Bumping up the dose usually doesn’t yield extra benefit but only causes jitters or tension that may degrade performance.
Using caffeine to stay awake when you’re not getting enough sleep is a poor idea. There is no evidence that caffeine reverses the effects of sleep deprivation. It’s not a reliable aid for students burning the midnight oil. And absolutely don’t trust it to keep you out of trouble behind the wheel of a car.
The best treatment for sleep deprivation is sleep.
Dr. Michael Craig Miller, editor in chief, Harvard Mental Health Watch
