Caffeine is the world’s drug of choice, with 80% of adults regularly consuming the stimulant. While caffeine does have some positive effects, like enhanced alertness, better mood, and improved exercise performance, it has some downsides too, especially if you drink too much.
In one study, researchers gave healthy men and women varying doses of caffeine at different times and found that the caffeine spiked cortisol levels throughout the day. The researchers were also interested to see whether or not participants could build a tolerance to caffeine that would eventually prevent these increases in cortisol. They found that while the cortisol responses were less severe over time, they never fully went away.
Caffeine can also interfere with sleep. According to another study, caffeine reduces the quality of your sleep by as much as 10% and the amount of sleep you get by almost 40%. And these effects can persist for three to five days after you’ve consumed it.
Although there are many different sources of caffeine, coffee tends to be the major contributor to a high caffeine intake. While moderate consumption is OK, it becomes a problem when the amount of caffeine you’re getting equals the amount in two to three cups of coffee. And that number drops for people who are more sensitive to caffeine.
It’s best to stick to no more than 200 milligrams—the amount in around 16 ounces (or Starbucks’ Grande size)—per day or switch to a caffeine-free alternative. If you’re addicted to caffeine or currently consuming well over the recommended limit, Ellen Vora, M.D., a holistic psychologist with a functional medicine approach to mental health, recommends gradually reducing your overall caffeine consumption and cutting off your intake earlier in the day, by 11 a.m. or 12 p.m. at the latest.