For 64 percent of American adults, not a day goes by where they don’t consume at least one cup of coffee. When they sip on brew, bean freaks are also consuming the most popular drug in the world: caffeine. A single cup of coffee contains between 95 to 165 milligrams of this natural stimulant, which has some impressive effects, like increasing alertness and enhancing the consolidation of long-term memories. However, the benefits coffee bestows on the drinker don’t negate the fact that it’s still an addictive drug.

And because of that, when a person does quit drinking coffee, the neurochemistry of addiction can pretty much guarantee they’ll go through withdrawal.

Typically, caffeine affects the body for three hours after it’s consumed. Withdrawal symptoms, meanwhile, begin to take effect 12 to 20 hours after a coffee addict’s last cup. They’ll be at their worst two days after that cup, but they can last for up to a week.

University of Vermont scientists discovered in 2009 that the symptoms that accompany this withdrawal, which include headaches and a sense of fatigue, are caused by changes to blood flow in the brain caused by caffeine. By measuring brain electrical activity and blood flow velocity in participants right after they consumed caffeine and after it had cleared their bodies, the researchers found that stopping caffeine consumption stopped increases cerebral blood flow. This, in turn, is correlated with drowsiness, decreased alertness, and headaches.

It may feel like this.
It may feel like this.

And then there are the mood swings, which are also caused by changes in the post-caffeine brain. Consuming caffeine causes a boost in dopamine, igniting the brain’s pleasure circuits. This burst of dopamine improves mood — and kicks off the reward system, the process that creates dependency on drugs. When the brain stops getting its fix of coffee-induced dopamine, its owner is going to get real grumps.

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Ultimately, caffeine’s energy boost comes down to its effect on the central nervous system. In the brain, caffeine blocks adenosine receptors, which are neuromodulators that regulate the activity of the central nervous system by binding a chemical called adenosine. When this happens, neural activity slows down and a person gets tired. But when caffeine blocks these receptors from grabbing adenosine, neural activity actually speeds up — and causes the adrenal glands to produce more adrenaline. This gives a coffee drinker that boost of energy and increased attention.

The brain, however, doesn’t want that caffeine hack to happen. In a study on the effects of caffeine on the brains of mice, researchers found that continuous caffeine consumption can result in an increased number of adenosine receptors. It’s thought that these extra receptors emerge so that adenosine has a greater chance of actually binding to a receptor that hasn’t been blocked by caffeine. Scientists hypothesize that this process may explain why long-time coffee drinkers develop a greater tolerance for caffeine, and end up drinking more of that energizing brew.

What this means for someone quitting coffee is that the former coffee-addict is going to feel fatigue — the brain has to work on its own without that burst. However, that switch could eventually mean more rest. Caffeine consumed up to six hours before bedtime has disruptive effects on sleep, and at its most extreme, insomnia. Quitting coffee may give you a killer headache, but at least you’ll be able to sleep at the end of the day.

Photos via Giphy, Flickr / Josh Parrish