How Late Can I Drink Coffee Before It Starts Messing With My Sleep?

It’s a reasonable question. Caffeine is famous for its stimulant properties: it blocks the effects of adenosine, a naturally occurring chemical that promotes our sleep drive, while reducing levels of melatonin. It can even increase levels of anxiety. Basically, it does just about everything it can to stop us from going to sleep – and while that may be useful in the short term, it’s fair to wonder whether it’s really healthy in the long term.

So… what’s the tea on coffee?

Coffee: the sleep killer

We drink coffee to keep us alert and awake – so it might seem strange that it’s associated with feeling more tired throughout the day. But it’s true: “Caffeine typically prolonged sleep latency, reduced total sleep time and sleep efficiency, and worsened perceived sleep quality,” reported one 2017 systematic review of the links between caffeine consumption and sleep quality.

Now, in a way, this isn’t surprising, right? You have a bad night’s sleep, so you drink more coffee – of course there’s a correlation between the two. But there’s good evidence that this relationship goes both ways, with caffeine abstinence for even just a single day resulting in sleep of significantly better quality and duration, and reduced sleep latency.

In other words: it’s not just that you’re increasing your caffeine intake because you’re tired. You’re also tired because you’re increasing your caffeine intake.

“If you find yourself struggling to fall and stay asleep when tired, look at your entire caffeine intake and see how much is getting into your system,” Abhinav Singh, medical director of the Indiana Sleep Center in Greenwood, Indiana, told Sleep Foundation in 2023.

“Start to reduce or eliminate as much as possible,” he advised. “There are hidden sources of caffeine that are present everywhere, including chocolate, workout drinks, body washes, and face creams.”

It’s not just a question of quantity, however. You can reduce your coffee intake to just a single cup a day – but if it’s too close to bedtime, you’re probably still in for a restless night.

Oh – and “too close to bedtime” is probably quite a lot earlier than you think.

When should I have my last cup of coffee?

The question of precisely when to bin the beans each day is, like most things, too individual to issue a perfectly applicable blanket statement. A lot of it comes down to your genetics: people with two copies of a particular variant of the CYP1A2 gene – also known as the “coffee gene” for reasons that will become obvious – are able to metabolize caffeine faster than most of us, who only have one.

“Someone who metabolizes caffeine slowly,” on the other hand, “should probably avoid evening caffeine if they want a good night’s rest,” registered dietitian Anthony DiMarino told Cleveland Clinic. 

Why? Well, “it can take two to 10 hours for just half of caffeine’s effects to wear off,” DiMarino explained. “This ‘half-life,’ as it’s known, varies from person to person.”

So, say you have a pretty normal metabolism for caffeine – not super fast; not super slow; let’s call it a six-hour half-life. That nice cup of coffee on the way back from work at 6 pm? Half of its caffeine content is still in your system at midnight. A quarter is still there at 6 am the next morning.

If you’re sensitive to caffeine, that’s going to have a big effect on your sleep. And the real kicker? You likely won’t even realize just how big it is until it’s too late: “People tend to be less likely to detect the disruptive effects of caffeine on sleep when taken in the afternoon,” explained Christopher Drake, a board-certified sleep specialist, professor of medicine at the Michigan State College of Human Medicine, and Director of Sleep Research for Henry Ford Health, back in 2013.

Overall, therefore, sleep experts generally advise cutting yourself off at around 2 or 3 pm, assuming you live a standard nine-to-five, bed by about 11 pm kind of life. That may seem early, but there’s at least some evidence that drinking caffeine even six hours before bed is still enough to interfere with sleep.

“Research on the exact timing caffeine’s impact on sleep is limited,” said Rashad Ramkissoon, a primary care physician at Houston Methodist, in 2023. But “when it comes to getting quality sleep, it’s better to be safe than sorry.”

Coffee, or sleep?

Despite coffee’s famed ability to keep us awake, there is one thing that’s even better for perking us back up again when it all gets too much: a nap.

“There is no substitute for sleep,” wrote Kimberly Fenn, Professor of Psychology at Michigan State University, in a 2023 article for The Conversation.

That was the finding from years of research at the University’s Sleep and Learning Lab, in which Fenn and her students investigated the effects of sleep deprivation and how well various interventions could counteract them. The results for caffeine were – well, pretty much exactly what you would have expected: “If you are sleep deprived, caffeine may help you stay awake and play Candy Crush,” Fenn wrote, “but it likely will not help you ace your algebra exam.”

Go too long without sleep, though, and even this level of caffeinated consciousness will elude you. 

“The performance advantage conferred by two daily 200 [milligram] doses of caffeine was lost after three nights of sleep restriction,” Tracy Jill Doty, a research scientist at Walter Reed Army Institute of Research, explained back in 2016. That’s no small dose – it’s the equivalent of about four cups of coffee a day, and the upper limit recommended by the Food and Drug Administration (FDA).

“These results are important, because caffeine is a stimulant widely used to counteract performance decline following periods of restricted sleep,” Doty said. “The data from this study suggests that the same effective daily dose of caffeine is not sufficient to prevent performance decline over multiple days of restricted sleep.”

So, while coffee has its place for keeping us up and kicking, we certainly shouldn’t rely too much on it – not only will it interfere with your sleep in the short term, but its stimulant effects simply aren’t powerful enough to play the long game. So, snuggle down, pick up your favorite spoon, and tuck in for the night. Your brain will thank you in the morning.

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.