What Happens To Your Body When You Drink Coffee?

what happens when you drink coffee

Drinking coffee has become a habitual part of millions of people's morning and afternoon routines. After World War II, "coffee breaks" were even written into some union workers' contracts. And why shouldn't they be?

Coffee stimulates cognitive abilities, sharpens focus, and helps to stave off mid-afternoon sluggishness. All this and it tastes good too. So how does this magical elixir wield such power?

Caffeine takes most of the credit—or the blame, however, the case may be—. But, according to at least one study, coffee, with its hundreds of complex components swirling in every cup, has more biochemical reactions at work than we first believed. And it affects virtually every system in your body.

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Immediate Effects On The Pulse And Blood Pressure

Blood pressure will increase shortly after the first sip. The compounds in coffee, caffeine being just one of them, are easily and rapidly absorbed into the bloodstream. How much of an increase depends on how often a person drinks coffee.

Children and those who rarely or never drink it may be quite sensitive to its effects and that first sip may initiate a brief spike in blood pressure. Regular adult coffee drinkers, however, have somewhat acclimated themselves to this rapid coffee influx. Hence, are not as likely to have as large an increase.

After one cup of coffee, a person's heart rate, or pulse, may, in fact, slow down because of the temporary increase in blood pressure. However, if more than one cup is consumed, the heart rate may increase too.

For normal healthy adults, this isn't usually problematic. For those with heart conditions or are being treated for elevated blood pressure may want to talk to their doctor about how coffee may interfere with their health management.

Interestingly enough, caffeine isn't necessarily the culprit for increased blood pressure. In a Harvard medical study, straight doses of caffeine did not provide the same increase in blood pressure to test subjects as did a triple espresso with an equivalent amount of caffeine.

Furthermore, even non-caffeinated coffee provided a spike in blood pressure which indicates caffeine may not be the sole chemical mechanism at work.

After About 5 Minutes: Effects On The Gut, Stomach, And Bowels

Coffee is stimulating in more ways than one. Between five and twenty minutes after drinking a cup of coffee, intestinal muscles in the colon begin to contract.

It was initially thought that caffeine was the main reason for the increase in bowel activity, but studies have shown that subjects given decaffeinated coffee produced similar results as fully caffeinated coffee.

So if caffeine isn't the reason for a stimulated digestive system, then what is? Firstly, the gastrocolic reflex reacts to anything you put in your stomach, whether it is food, water, or coffee (which is mostly water).

As soon as something hits your stomach this reflex becomes activated which puts the bowels in motion. Secondly, remember those hundreds of compounds that were in each cup of coffee?

Some of those compounds, particularly N-Alkanoyl-5-hydroxytrptamides (C5HTs) and chlorogenic acids (CGAs), cause the stomach to secrete acids to help with food digestion. Different roasts of coffees have different amounts of C5HTs and CGAs.

For instance, dark roasts have less of these stomach stimulating acids as they are probably lost during the prolonged roasting time. If it is not obvious already, medium roast has more of such acids.

What all the biochemistry means is that coffee has components that are independent of caffeine which kick-start the digestive system at a faster rate.

After About 30 Minutes

After the colon has absorbed the coffee compounds, they go into the bloodstream and travel through the rest of the body fairly quickly. This happens usually around 30 minutes after consumption. 

Here's how coffee affects various body systems at that 30-minute mark.

Eyes and Vision

As mentioned earlier, coffee with its caffeine and hundreds of other complex components work as a stimulant to our body systems. Caffeine stimulates the adrenal glands which release adrenaline into the blood-stream.

Adrenaline is the body's natural fight-or-flight mechanism. It increases your pulse to deliver oxygen more quickly to your heart, muscles, lungs, and brain. It also dilates the pupils in the eyes which may temporarily moderately improve vision.

Too much caffeine can cause the opposite effect in your eyes and make your vision blurry.

Long-term caffeine over-consumption—those that drink more than 400mg of caffeine per day or more than 4 cups of coffee per day for a prolonged amount of time—can be susceptible to eye damage from increased pressure on the eyes, a condition called glaucoma.

Brain and Cognitive Abilities

The effects that coffee and caffeine have on the brain is basically everything we've come to want and expect from our favourite hot morning beverage.

First and foremost, it makes us feel less sleepy. The reason for this is that caffeine blocks the accumulation of adenosine, a naturally occurring chemical in the brain which signals the body to sleep.

As a stimulant, caffeine fires up the central nervous system by activating the release of neurotransmitters. The effect of all this cranial chemical activity is that coffee and caffeine make the brain feel more alert. You will find yourself able to concentrate more fully.

There is another happy effect that coffee, or more specifically caffeine, in this case, have on the brain: Improved memory.

A John Hopkins University study found that not only does coffee strengthen memories. But it can make specific and detailed memories more difficult to forget. The effects can last over 24 hours from the initial caffeine consumption.

Researchers aren't sure yet how caffeine enhances memory but think it might have something to do with the blocking of the previously mentioned adenosine.


It's hard to measure how much enjoyment that first cup of coffee can bring to a tired and wanting body, we just know that we love it. But there are some studies that have attempted to quantify exactly how coffee and caffeine affects our mood.

Serotonin is a naturally occurring chemical neurotransmitter in the body. People who have low serotonin levels can experience depression and anxiety. Caffeine's mechanism of action works in a similar way as some prescription antidepressants in that it can increase serotonin levels and serotonin receptors.

Furthermore, a study has suggested that women who drink an average of 2 to 4 cups of coffee per day were 15-20% less likely to report symptoms of depression. Decaffeinated coffee did not provide the same results.

Too much caffeine can have the negative reaction on the mood, surpassing feelings of pleasantness and leading straight to agitation, jitters, and anxiety.

Too much caffeine can also interfere with a body's ability to fall asleep which can also have detrimental effects on mood and lead to feelings of depression.

Coffee withdrawals for habitual coffee drinkers is a real problem, as their body chemistry has been acclimated to the higher levels of serotonin and serotonin receptors. If the supply is suddenly cut off, withdrawal symptoms can occur which may include irritability, anxiety, and headaches.

After 6 And Up To 24 Hours: How Caffeine Is Eliminated From The Body

As great as most of the effects of coffee and caffeine have been, you can't go around drinking coffee all day or else you'll never be able to get to sleep.

Even though it varies from person to person, the average half-life of caffeine, that is, the amount of time for half of the caffeine to be eliminated from the body is 5 to 6 hours in healthy adults.

Some lifestyle factors can affect the half-life such as heavy cigarette smokers or pregnant women, which can decrease the half-life up to 15 hours.

Caffeine is removed through the kidneys by way of urine. Caffeine has been shown to have a small diuretic effect which stimulates the kidneys to release more water.

Since caffeine had activated the flight or flight adrenaline response, once it has been eliminated, the body can go through a withdrawal or "crash" episode in its absence. Previously blocked adenosine levels suddenly rise which triggers feelings of tiredness or signals for the body to sleep.

The body's response to the elimination of caffeine is not harmful and won't last long while your body adjusts itself to a caffeine-free system. If you are very sensitive to the effects of caffeine the feelings of withdrawal may be more pronounced.


Caffeine, especially when combined with coffee, can be beneficial as a mind, body, and even mood. It gives the coffee drinker enhanced cognitive function and feelings of contentment.

But as with most things, too much of a good thing can actually be a bad thing. What was perceived as increased concentration can turn into feelings of anxiety, contentment can turn into agitation.

As the adage goes, moderation in all things is best, and coffee is no exception.

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