It Helps. Caffeine combats drowsiness by tricking your brain into feeling alert. It temporarily blocks adenosine, a naturally sedating brain chemical, to prevent fatigue. “If you don’t get a full night’s sleep, you’ll wake up with more adenosine in your brain than you normally would,” explains Timothy Roehrs, PhD, of the Sleep Disorders and Research Center at Henry Ford Hospital in Detroit. A hit of caffeine neutralizes adenosine and helps you feel less sleepy. If you’re a regular coffee guzzler, though, you may need an extra boost to counter your late night. “As tolerance develops, the brain makes more receptors for adenosine,” says Roehrs. “So you need more caffeine to block the added receptors.” These are the signs you’re drinking too much caffeine.
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It Helps. People who don’t use caffeine regularly “usually become significantly more alert and better able to perform cognitive and motor tasks — like paying attention during boring or rote routines such as typing — if they’re given the proper caffeine dose,” says Laura Juliano, PhD, a professor of psychology at American University in Washington, DC. (For people who do use caffeine regularly, however, it offers few, if any, benefits.)