How Caffeine Affects Your Body and Mind

Whether you’re dragging yourself out of bed on a dreary morning or trying to survive the world’s longest staff meeting, caffeine often seems to be a good solution. But what’s really happening when you down a cuppa?

Your body absorbs caffeine quickly and efficiently. It takes just 15 to 20 minutes for caffeine to hit your bloodstream, but its effects can last anywhere from one to 10 hours.

“Caffeine is a stimulant, and it affects your body in several ways,” says registered dietitian Beth Czerwony, RD, LD. “It can increase your energy and help you power through your day — but you can also overdo it.”

How caffeine impacts different parts of your body

Caffeine can help you feel more awake, alert and focused. It can even improve your mood. But too much caffeine can have negative effects, like raising your blood pressure, upsetting your stomach and making you feel jittery. In rare cases, caffeine overdose can even be fatal.

Here’s a look at what caffeine does to various systems in your body — both the good and the bad.

Caffeine and your brain

As a stimulant, caffeine revs up your central nervous system, which manages just about everything your body does, from thinking to moving. Its effects can be both positive (more energy) and negative (less sleep). Let’s take a look.

Wakefulness and alertness

“Caffeine blocks the effects of adenosine, a brain chemical that contributes to tiredness,” Czerwony explains. “That gives you that pick-me-up to stop feeling so sleepy.” The effects can be powerful: 300 milligrams (mg) of caffeine can significantly improve daytime alertness, even in people who are partially sleep-deprived.

Improved focus

When adenosine is blocked, two other brain chemicals become active. “Both dopamine and norepinephrine stimulate your concentration and focus,” Czerwony continues. This may even help adults with ADHD focus and concentrate better, particularly while doing repetitive tasks.

Better mood

Yes, caffeine really can lift your vibe! Both dopamine and norepinephrine have been shown to have antidepressant effects, so in low doses (20 to 200 mg), caffeine is thought to lead to generally positive feelings.

Headache relief

Caffeine is a vasoconstrictor, meaning it narrows your blood vessels. In small amounts (100 to 150 mg, or a small cup of coffee), these effects can help relieve the pain of tension headaches and migraine headaches, which involve a widening of the blood vessels to your brain. (But it cannot help with other types of headaches.)

And there’s another side to the coin: Caffeine can also cause headaches, like if you drink too much, quit cold turkey or are just particularly sensitive to it.

Anxiety

Low doses of caffeine can boost your mood, but too much can have the opposite effect — and the more you consume, the worse you feel. “Because caffeine excites your central nervous system, it can lead you to feel anxious, jittery and irritable,” Czerwony warns. Cutting back can keep those side effects in check, but if you have an anxiety disorder, you may need to avoid caffeine altogether.

Insomnia

Caffeine can help you get through a sleepy day, but too much of it can keep you up at night. “It can become a vicious cycle,” Czerwony cautions. To avoid disrupting your slumber, avoid caffeine in the afternoon and evening.

Caffeine and your heart

Most studies on caffeine and heart health look at the benefits of coffee, not caffeine — which means other caffeinated products may not have the same benefits. That said, moderate coffee drinking is thought to be good for the heart and may lead to a decrease in hypertension and high cholesterol.

Higher blood pressure and heart rate

Because caffeine causes your brain to release more norepinephrine, it can lead to mild increases in blood pressure and heart rate. Most people can handle these effects, but it can spell trouble if you already have heart problems. And as always, higher amounts of caffeine cause more issues: Regularly consuming 400 mg or more of caffeine may increase your heart rate and blood pressure over time.

Heart palpitations

One study found that drinking coffee was associated with a 54% increase in heart palpitations, which can make you feel like your heart is racing, fluttering or skipping a beat. Though they aren’t usually dangerous, heart palpitations can be alarming and uncomfortable. You may be especially prone to them if you have anxiety.

Caffeine and your digestive system

Too much caffeine can cause stomach issues. It has a laxative effect, meaning it can make you poop, and it can also lead to heartburn and acid reflux. Getting your caffeine in from coffee can intensify these effects.

Laxative effect

“Caffeine stimulates the gut and helps food move more quickly through your digestive tract,” Czerwony explains. Plus, other compounds found in coffee make it especially likely to make you poop. This can help promote healthy bowel movements, but if you’re sensitive to caffeine, beware of the possibility of diarrhea.

Heartburn

Caffeine can increase your body’s production of stomach acid and relax your lower esophageal sphincter, a muscle that prevents acid from traveling back up your esophagus. The result? Uncomfortable and even painful heartburn symptoms. And acids in coffee in particular can add to the issue.

Caffeine’s effect on other body systems

There are many other ways caffeine can impact your body, but here are a few additional effects worth highlighting.

• Makes you pee. “Caffeine is a natural diuretic, a chemical that helps your body eliminate excess fluid,” Czerwony explains. But this effect may be lessened if you regularly consume caffeine, like by drinking coffee or tea every day.
• Can contribute to dehydration. On its own, caffeine isn’t likely to dehydrate you, but just don’t sip on caffeinated beverages all day and forget about water! Make sure to continue to drink plenty of water to stay hydrated.
• Lessens calcium absorption. “Caffeine decreases your body’s ability to absorb calcium,” Czerwony says. “This can be bad news for your bones, which rely on calcium to stay strong and ward off osteoporosis.” Moderate caffeine is thought to be safe for your bones, but consuming a lot of heightens your risk — especially if you don’t eat enough calcium to begin with.

Final thoughts on the effects of caffeine

Caffeine is a drug, and too much of it can cause unpleasant side effects. It can even damage your heart and central nervous system. So, it’s always best to consume it in moderation.

With some trial and error, you can find a balance that leaves you alert and energized without the unpleasant side effects.

“There are benefits to caffeine, but it can really get away from you if you’re not careful,” Czerwony reiterates. “Too much of a good thing is still too much.”