Amanda Norcross • May 03, 2021
Ever wondered why you can drink a cup (or multiple cups) of coffee, but still feel tired enough for a nap? We asked medical experts why coffee makes some of us sleepy, and how to avoid feeling tired after drinking it (so that we can enjoy all of the health benefits of coffee).
"Coffee can make some people sleepy because it blocks adenosine receptors in the brain," explains Chris Airey, practicing physician for the NHS and Medical Director at Optimale. "Adenosine makes you drowsy to prepare for sleep, but coffee can bind to adenosine receptors. When the caffeine wears off, there are adenosine molecules that bind to the adenosine receptors, causing you to feel tired after drinking coffee."
"Coffee is a mild diuretic because the caffeine in coffee increases the blood flow to your kidneys, which stimulates them to release more water," explains Chelsea Rohrscheib, head neuroscientist and sleep specialist at Tatch. "While you can expect to urinate more after drinking coffee, clinical research has shown that consuming a couple of cups a day doesn't cause fluid loss in excess of the volume ingested."
However, coffee can be problematic if you're already dehydrated or drinking coffee with low water content, such as espresso, without consuming additional fluids, she explains. Dehydration can cause you to feel sluggish, and lead to other ailments such as headache and dizziness. The best thing you can do to avoid feeling tired after coffee—and to feel better overall—is drink enough water.
"Caffeine may also affect your glucose metabolism," explains Dr. Airey. "This can lead to higher blood sugar levels, which causes fatigue." That's why it's important to eat when you drink coffee. "If you notice yourself getting sleepy when you drink coffee and you suspect your blood sugar is low, try eating a healthy snack like a piece of fruit or whole-wheat crackers," suggests Rohrscheib.
Too much sugar by way of artificial sweeteners and syrups can cause you to feel tired after you drink coffee. "These sweeteners cause a rapid spike in blood sugar followed by a sharp decline," explains Rohrscheib. "This quick change in blood glucose levels can leave you feeling tired and sluggish."
You don't have to suddenly start drinking black coffee, though. Try lessening the amount of sugar you add to your coffee, or explore more light roasts, which can be naturally sweet. For instance, Kenyan roasts have a reputation for being very fruity and sweet. You might also like Ethiopia Natural and Guatemalan roasts.
"Caffeine consumed in large amounts has been shown to increase stress levels and increase cortisol release in clinical studies," says Rohrscheib.
So how much is too much? Rohrscheib advises two cups or less, while most research suggests 400 milligrams (about four cups) per day is a safe amount of coffee to consume. But that doesn't necessarily mean you should drink four cups each day. Remember that everyone metabolizes coffee differently, and someone who drinks coffee every morning will react differently than someone who's drinking it for the first time. It's best to determine the appropriate amount based on how your body reacts to each cup of coffee.
"The most beneficial time to have your coffee is one hour after you wake up," says Rohrscheib. "Additional coffee consumption has diminishing returns the later you consume it in the day."
Believe it or not, you can actually maximize the effects of caffeine by taking a coffee nap. Here's how to do it.