What Happens To Your Body When You Drink Caffeine

Turns out caffeine doesn't actually give you superpowers, but what exactly happens when we drink it?

Young woman having a cup of coffee
Photo: Getty Images / Marko Geber

Whether consumed out of necessity to get you moving or just savored as a step in your morning routine, most of us can't imagine a day without caffeine. It's generally accepted that caffeine is probably not a magic elixir, but how can it power us through a morning of dull meetings, and why do we get headaches if we skip it? Why does it have us running to the bathroom, and when should we cut it off? We're breaking down all the caffeine-fueled questions here.

First, How Much Caffeine Can We Consume in a Day?

Current Food & Drug Administration (FDA) recommendations advise healthy adults consume no more than 400 mg caffeine per day. To put this in perspective, one cup of brewed coffee contains about 90 mg caffeine, so aiming for no more than 4 8-ounce cups of regular coffee daily is a good rule of thumb. Don't forget to include caffeinated teas, energy drinks and dark colas (including diet) in this count, and keep in mind that caffeine from less suspecting foods and beverages, like chocolate and decaf, also contribute to your daily amount.

For those who are pregnant, it's recommended to limit caffeine to no more than 200 mg per day, or about two 8-ounce cups of regular brewed coffee (or up to 300 mg per day while breastfeeding). Note that caffeine is discouraged for kids under the age of 12 and teens shouldn't consume more than 100 mg per day.

What Happens To Your Body When You Drink Caffeine?

You feel alert and energized

Caffeine's claim to fame is related to a number of biochemical processes that occur soon after consumption. For one, caffeine can blunt the effect of adenosine, a chemical in the brain responsible for making you feel tired. As a result, you may feel more alert and less groggy, especially if you didn't sleep well the night before. But this quick-fix won't last and caffeine loses its effect after a few nights of poor sleep. Plus, consuming too much caffeine can eventually interfere with the quality of your sleep in general (more on this later).

Caffeine also triggers the release of the stress hormone epinephrine (a.k.a. adrenaline), which activates the body's "fight or flight" response. Our heart rate increases, blood supply to our muscles increases, and glucose is released into the bloodstream, all of which can make us feel a sudden boost in energy. Keep in mind, this buzz is short-lived. The only way to actually "energize" the body is by consuming macronutrients (carbs, proteins and fats) from foods. Take this as a reminder to eat breakfast alongside your caffeinated beverage of choice.

You'll find yourself in the bathroom sooner than later

Caffeine is a diuretic, meaning it tells the kidneys to release water and produce urine. You may find yourself in the bathroom soon after your chai tea latte (and maybe a couple more times throughout the morning), but contrary to popular thought, caffeine likely won't cause dehydration. In fact, caffeinated beverages in moderate amounts count toward your daily fluid intake. And while it's often assumed the caffeine in coffee helps you poop, recent research suggests it's coffee's influence on our microbiome, and not necessarily the caffeine, that has a laxative effect.

It can improve mood…and also mess with your mental health

When we consume caffeine, our brain receptors become more sensitive to dopamine, the "happy hormone". The resulting mood boost is temporary and returns to baseline after the caffeine is out of our system, though research suggests caffeine can reduce the risk of depression when consumed in moderate amounts. It's important to note that caffeine can have the opposite effect, too. Excessive caffeine can lead to feeling agitated and edgy. For some, it can make anxiety, panic and other mood and mental health disorders worse.

It can make other medical conditions worse

As a central nervous system stimulant, caffeine can raise blood pressure and heart rate, a concern for those with certain heart conditions like arrhythmias. People living with diabetes may experience blood sugar fluctuations after consuming caffeine as it can impact insulin sensitivity, but recent research has mixed findings on this. Caffeine can also exacerbate symptoms in those with gastrointestinal disorders, like IBS or acid reflux.

You can become mildly dependent on it

The rise in dopamine after consuming caffeine is also the reason we might feel "addicted" to coffee. If you've ever been hit with a mid-morning headache or feel irritable after missing your morning brew, you know what we're talking about. Feeling hooked on caffeine is not recognized as a true addiction, but because of the mild withdrawal symptoms that can be experienced in its absence it may be considered a dependency. If you do decide to quit caffeine, withdrawal symptoms, like headaches and fatigue, shouldn't last more than a few days.

It can improve your workout

Caffeine is considered a legal ergogenic aid (a.k.a. performance enhancing substance) at certain doses. It appears to enhance performance of aerobic (like jogging) and anaerobic (like strength training) activities, and for both professional athletes and casual exercisers alike. Benefits are seen at doses of 3 to 6 mg/kg body weight (about 16 ounces brewed coffee for a 150-pound adult), consumed about an hour before a workout. And while we lack sufficient evidence that caffeine increases metabolism enough to promote weight loss, a recent study found drinking a cup of strong coffee 30 minutes before an aerobic workout may increase fat burning.

You could lose precious sleep

One of the more costly side effects of caffeine is its impact on a good night's rest. Consuming caffeine in high amounts or too close to bedtime can impact overall sleep quality, keep us from falling asleep and reduce hours slept. While some may do just fine with a mid-afternoon perk-me-up, it's generally advised to cut off the caffeine at least 6 hours before bedtime, as this is about the time it takes for our bodies to metabolize it. For those with sleep problems, like insomnia, consider reducing overall caffeine intake or try cutting it off by noon.

The Bottom Line

While caffeine can have some seemingly magical effects, it's no miracle drug and might be harmful in excessive amounts. While it may temporarily increase alertness, energy and mood, it can also wreak havoc on your sleep, may be risky for those with certain chronic conditions and can make anxiety worse. Like with many foods and beverages we enjoy, moderation is key with caffeine, too.

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