If you wander into a college library on a weekday around midnight, you’ll be met with the following scene: Students occupy every table, though they are barely visible amid the piles of textbooks, loose-leaf, and laptop computers. Peeking over their makeshift bunkers, you see they’re dressed in sweats, their hair is unkempt, and the dark circles under their eyes extend past their cheekbones. Despite their exhausted appearance, there remains a fire behind their eyes. They clack away at their keyboards with tremendous speed, stopping only to reach for the Venti Starbucks coffee on the table beside them.
Many college students rely on caffeine to get through the day. They are not alone in this – it is estimated that over eighty percent of Americans consume caffeine on a daily basis. You yourself likely jumpstart your day with about 95 milligrams of caffeine, the amount contained in your morning cup of joe. Caffeine consumption is integrated into our daily routines, so commonplace that it’s almost assumed. Have you ever stopped to wonder why caffeine has such an energizing effect? How exactly does this powerful substance fuel undergrads’ all-nighters and wake you up for work every day?
The short answer is that caffeine is a psychostimulant. This may seem surprising. The word “psychostimulant” is usually associated with prescriptions like Ritalin or illicit uppers like cocaine, but caffeine technically belongs to the same class of drug. Psychostimulants increase alertness, wakefulness, locomotion, and activity of the sympathetic nervous system. This is the system preps the body for “fight-or-flight” responses, basically revving it up for action. It drives increases in heart rate, body temperature, and breathing rate. It also causes the liver to release stored sugars into the body, making them available for use.
Of course, though all psychostimulants elicit these effects, they do so at dramatically different intensities. To state the obvious, drinking a cup of coffee is not like doing a line of cocaine. These drugs have different chemical properties and work through different mechanisms in the body.
Caffeine works by blocking the action of adenosine, a chemical in the brain that causes drowsiness. Our body fuels its cells with adenosine triphosphate (ATP). As our cells use their ATP, they break it down into its component parts, including our drowsiness chemical adenosine. So as our cells burn through their fuel, our adenosine levels rise. Adenosine then binds to brain cells, known as neurons, and slows down their activity. In this way, they use less energy and we begin to feel “sleepy.”
Caffeine has a chemical structure very similar to adenosine. When introduced inside the body, it occupies the receptors that adenosine usually binds to. This is known as “competitive antagonism,” as the caffeine and adenosine are competing for the same binding sites. When caffeine steals adenosine’s seat, it amps up cellular activity rather than toning it down. Instead of becoming sleepy and slow-witted, we are reenergized and focus more clearly. We suppress our body’s need for sleep and are able to stay up through the night to finish that 20-page paper that’s due tomorrow.
While convenient for a quick pick-me-up, caffeine becomes less effective when used chronically. While you maintain your habit of two cups of coffee a day, your neurons are installing more and more adenosine receptors. With more receptors, more adenosine is able to bind despite the caffeine competing with it. Your body builds up tolerance to caffeine. You now need three cups of coffee, then four, to fill those receptors and block out adenosine’s tiring effects. Furthermore, if you skip your coffee one morning, adenosine binds both the old and new receptors. This amplifies adenosine’s normal effects, causing headaches, nausea, irritability, and loss of focus. Your body has adjusted its function to compensate for your daily caffeine fix, and without it you experience withdrawal.
This reliance on caffeine for normal functioning is known as “physical dependence.” Physical dependence is characteristic of serious Substance Use Disorders (SUDs), including alcohol and opioid addiction. “Caffeine addiction” is not considered an official SUD because it lacks the clinically significant functional impairments and personal distress seen in other addictions. For instance, a “coffee addict” is unlikely to risk their job or social standing for a shot of espresso. That is not to say that caffeine dependence shouldn’t be taken seriously. So when you’re camped in the library for finals week, or when you’re brewing your morning java tomorrow morning, remember to practice moderation in consuming your favorite adenosine competitive antagonist.