For those who experience side effects of caffeine—insomnia or headaches, for instance—it may be best to avoid it or limit consumption. "It's been shown that people metabolize coffee differently based on genetic factors. Some people metabolize it quickly, and other people [metabolize] more slowly," Hensrud says. "So that may explain why some people are more susceptible to the side effects."
If those side effects get to be overwhelming, or you're just ready to kick the coffee habit, it is possible to slowly reduce your coffee intake without experiencing bothersome signs of withdrawal. Johns Hopkins offers an experimental caffeine withdrawal treatment program, in which participants gradually reduce their caffeine intake by 10 to 20 percent per week. "We do that by having them gradually substitute in noncaffeinated versions of what they're consuming," Griffiths says. Over the course of several weeks, he says, "most people can emerge from that caffeine free without experiencing many substantial withdrawal symptoms."
If you don't see yourself giving up coffee anytime soon, it's a good idea to try to estimate how much caffeine is in your cup, particularly if you buy yours at a restaurant or coffee shop. The website for Starbucks, for instance, lists nutrition information, including the amount of caffeine and calories contained in their beverages. While caffeine content can vary greatly depending on who makes it and what type of bean is used, for instance, a general rule of thumb in the United States is 100 milligrams of caffeine per 6 ounces of coffee, Griffiths says.
Related: Coffee isn't the only caffeine-containing drink that can impact health. Energy drinks, popular among the teen and college set, can negatively affect health if not consumed in moderation.