When You Drink Coffee Before Bed, This Is What Happens

Many people rely on their morning cup of coffee to help them wake up and get through the day. However, drinking it too late in the day can disrupt your sleep cycle and hinder your overall quality of sleep (via Self). That's because the main active ingredient in coffee is caffeine — a central nervous system stimulant that helps keep you awake by binding to the adenosine receptors in your brain.

"Adenosine is like a sleep-inducing molecule that your brain makes while you're awake," Dr. Ajay Sampat, a neurologist, sleep medicine specialist, and assistant clinical professor at UC Davis Health, told Self. "The longer you're awake, the more adenosine you have in your system." When caffeine binds to these receptors, however, it reduces adenosine's sleep-inducing effects and gives you a jolt of energy, causing you to stay alert and awake. 

While caffeine's effects are strongest within the first hour after consumption, it can take quite a while for it to completely leave your body. With that in mind, is it really risky to drink coffee before bed? What about in the afternoon?

You don't have to drink coffee within minutes of going to bed for this to occur to feel its lasting effects. Caffeine can stay in your system for hours at a time and can affect your sleep long after its stimulating effects wear off (via Well+Good). Exactly how long it stays in your system depends on the speed at which you metabolize caffeine.

For instance, if you're a fast caffeine metabolizer, you may be able to continue drinking coffee later on in the day than those who metabolize caffeine at a slower rate. According to Dr. Dan Reardon, who has studied coffee's effects, you should stop drinking coffee anywhere from 12 p.m. to 2 p.m. if it typically takes you longer to metabolize caffeine.

If you metabolize caffeine at a faster rate, however, your cutoff time can be closer to 5 p.m. "Let's not forget that even for a fast metabolizer of caffeine, there could still be a cumulative effect of drinking lots of coffee early in the day, which could slow down the rate at which they break down their caffeine later," Dr. Reardon told Well+Good. In that case, it's a good rule of thumb to stop drinking coffee around lunchtime.