What Is A Caffeine Crash? Plus, 4 MD Tips To Prevent It From Happening

Recently, one of my clients mentioned he had been feeling noticeably tired and irritable, especially in the afternoon. "Around 3 p.m., I get drowsy, and focusing on work feels impossible," he told me during a virtual consultation. The opposite problem occurred at night as he struggled to fall and stay asleep. 

Most Americans partake in some form of caffeine every day. That might include things like coffee, cacao beans, kola nuts, tea, yerba mate, sodas, and energy drinks. Some people take supplements that contain caffeine in capsules, tablets, or powders.

Regardless of its source, caffeine (in its most common, instant-release form) has nearly a 100% bioavailability when consumed orally, meaning that you absorb all of it into the bloodstream rather quickly. Its full effects kick in in about 45 to 60 minutes1 and can last three to five hours (or longer, if you're a slow caffeine metabolizer). Food can inhibit caffeine absorption, but only by a little bit. 

A few hours after drinking moderate or high doses of instant-release caffeine, many people experience a caffeine crash. Side effects vary in intensity from person to person, but include dozing off during the day, feeling irritated, and not being able to concentrate—the opposite of the desired effect people are drinking caffeine for in the first place.

For some people, a caffeine crash can also feel like you've spent the previous night bar-hopping, with side effects including gastrointestinal issues and sensitivity to light or sound.

All bodies are different, and so people respond to caffeine in various ways. That explains why your friend can have two cups of coffee at dinner and still fall asleep by 10 p.m., while your morning roast might keep you wired until bedtime. To understand why caffeine crashes occur, we need to look deeper at how the body metabolizes caffeine.  

As a naturally stimulating compound, caffeine fires up the central nervous system, allowing you to become more alert and focused.* You may have more energy. An increase in adrenaline may raise your heartbeat or blood pressure slightly. For most people, these physiological changes are temporary.  

But for some people, caffeine can create undesirable effects. Mild side effects of caffeine include feelings of anxiousness, restlessness, irritability, agitation, gut upset, and subpar sleep.

Why do some people experience these things after they consume caffeine while others handle it just fine? When you consume caffeine, a liver enzyme called CYP1A2 breaks it down. The gene that codes this enzyme varies greatly among people. Scientists divide people into three groups, depending on how quickly their livers metabolize caffeine: high, regular, and low metabolizers. 

For high (aka fast) metabolizers, this enzyme breaks down and helps clear caffeine very quickly. Low metabolizers, on the other hand, break down coffee at a much slower pace, so its effects stick around much longer.

Just like most things we consume, moderation is key. Caffeine carries potentially adverse effects, depending on how much you consume as well as your personal physiology and thus, sensitivity to caffeine. If you rely on your morning coffee to pull you through the day, you might find its energizing effects tapering off midday. On the other hand, eliminating caffeine cold turkey can create some unpleasant side effects of its own. 

When your blood sugar levels are all over the map, many side effects of a caffeine crash get amplified. When blood sugar levels spike and crash, you may feel cranky and sleepy, which can cause you to reach for caffeine.

Perhaps your problem isn't caffeine intake itself, but the form of caffeine that you're consuming. Trading one (or a couple) of your daily cups of coffee for a high-quality focus supplement that promotes sustained energy can help you avoid the afternoon slump.

If you're tired of having a caffeine crash and want to quit entirely, just be aware that going off caffeine cold turkey can be a monster. Undesirable side effects kick in about 12 to 24 hours after you stop consuming caffeine. They become most pronounced within one to two days, and can last for up to a week. These include sensitivity to sounds and light, tiredness, gastrointestinal upset, mood changes, and sometimes headache.

Poor sleep ranks high on the reasons people over-rely on caffeine and experience caffeine crashes. Not getting enough sleep can affect nearly everything, including reducing insulin sensitivity and increasing unwanted weight3. I've written about how poor quality sleep can affect gut health, and you're also more prone to suboptimal immune response4 when you don't sleep well.