Caffeine Metabolism


Have you ever thought about what is actually going on in your body when you throw back that energy drink or sip that coffee?

How is caffeine broken down and how does it affect your metabolism? How long does caffeine stay active in your system and why do people crave the stuff?
We’ll try to answer those questions and more in the simplest terms possible so that you can be an educated consumer when it comes to caffeine metabolism.

Caffeine From the First Sip

Caffeine easily passes through body membranes so from the first sip the caffeine is entering your bloodstream through the lining of your mouth, throat, and stomach.

It only takes 45 minutes for 99% of the caffeine to be absorbed through these membranes.

In humans, the half-life for caffeine is anywhere from 4 to 6 hours on average, which explains why the average energy drink or coffee’s effect lasts about 4 to 6 hours.

Things like age, medical conditions, and drug interaction can have an effect on the half-life.

Note: Humans also can have 3 levels of sensitivity to caffeine. This also determines how well you metabolize caffeine and to what degree its stimulating properties affect you. Read about those here.

Caffeine in the Blood Stream

While most research on caffeine has been conducted using animals, the data has been converted to show the most likely effect on the human body. As soon as the caffeine enters the body it is already being metabolized by the liver and broken down into theophylline, theobromine, and paraxanthine.

From there these chemicals travel throughout the body where they affect various body functions.

It’s in Your Genes

The speed at which caffeine is metabolized depends on specific genes. Research continues to discover gene variations that appear to be responsible for how long caffeine stays in the bloodstream.

People with a specific variation of the gene PDSS2 process caffeine more slowly than others. They, therefore, need less coffee for the same stimulant effects.

Caffeine in the Brain

The most studied of these is the way caffeine is similar to the molecule adenosine in the brain. The caffeine molecules bind to the adenosine receptors in brain cells and block adenosine from binding.


Adenosine plays a role in the sleep-wake cycle. When adenosine binds to enough receptors, it signals the brain that it is time for rest or sleep. Caffeine doesn’t replace the person’s need for sleep, but just covers up drowsiness symptoms that adenosine can no longer produce.

This also interacts with the dopamine system in the brain, which is the feel-good neurotransmitter. When adenosine is blocked by caffeine, the dopamine system works more efficiently.

Furthermore, elevated levels of adenosine in the blood cause the adrenal glands to release adrenaline. This stimulating hormone further adds to the feelings of alertness and energy.

Here’s a great TED-Ed video that explains what happens in the brain.

Caffeine’s Effects on the Body

Theophylline relaxes smooth muscles, which has been beneficial to those with asthma and is the reason why after drinking caffeine a person often feels the need to use the bathroom as it is affecting the smooth muscles of the colon.  Theobromine increases the amount of oxygen and nutrients that can be used by the brain and muscles.

Caffeine causes an initial contracting of artery walls (vasoconstrictor) but then relaxes this smooth muscle which has an overall vasodilator effect on the blood vessels. In other words, it opens blood vessels to allow for greater blood flow. src.

There have been many other researched effects of caffeine covered by Caffeine Informer, but the above represents the most researched and common.

Look here to find out how much caffeine would be deadly in humans.

Caffeine’s Exit from the Body

The caffeine metabolites are then filtered by the kidneys and they exit the body with the urine.

Caffeine has been shown to have a diuretic effect on the body, which basically causes the body to release more water in the urine.

However, new research suggests that this is only in people who have not built up a tolerance to the caffeine molecule.

When caffeine has exited the body or has been used by the various cells of the body the person can experience a “crash” that is caused by elevated levels of adenosine flooding the brain and dopamine now being repressed. This causes feelings of tiredness and fatigue. Prolonged use of caffeine also causes withdrawal symptoms.

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  • Rodrigo Barba

    I normally drink one cup of coffee bean coffee in the morning every day for the last couple of years. I am 32 and weight about 185. I started going back to school this semester and have been upping my caffeine dosage to two to three cups a day sometimes a latte or some sort of drink with espresso in it. Out of nowhere I had an anxiety attack and I knew it was due to the upgrade in caffeine dosage. I noticed that ironically I wasn’t becoming more tolerant I was becoming more intolerant, to the point that even if I had one sip of regular coffee in the morning I would become overactive and really hyper. Is this my body’s way of saying to chill out for awhile? If so, could I detox from coffee and then go back to at least my regular cup in the morning and only that? Thanks

  • Ted

    Hi Rodrigo, This has to do with your genetics and changes to your sensitivity level. Detoxing will not help. You could try decaf or halfcaf

  • Annie

    Hello. Another sleepless night after taking a couple of sips from my husband’s sweet tea. I have been diagnosed with “fatty liver”. I’m not an alcohol drinker therefore; my Dr seems to think it’s from being overweight. I’m 5’0″ and weigh 160 lbs. My liver enzymes are currently elevated. I’ve had lab work to check for other causes to no avail. She just tells me to exercise and watch my diet. I used to be able to drink at least one glass of tea per day with no side affects.(Even if I drink something caffeinated early in the day, I pay for it at night) Now after just taking a couple of sips, it keeps me up at night. I fall asleep fine, but then I’m wide awake after about four hours of sleep. Could my elevated liver enzymes been causing this?

  • Ted

    Hi Annie, Caffeine is metabolized by the liver, so if your liver isn’t functioning properly it will cause caffeine to stay active in your system much longer.

  • I had a UBIOME gut test done and the results of one part of the test were maybe understandable IF i could understand what they mean? Specifically I know i have always BEEN historically sensitive to caffeine, and keep trying to quit even decaf. These KEGG gen and etc pathway analysis I think mean I am EXTREMELY EXTREMELY slow to metabolize caffeine and i guess steroid? OR (which I guess would not make sense) I am 8 times more efficient at it? Anybody have any insight to this “result”, the Ubiome folks are actually useless and just throw pile of reference stuff up on the site but no real value or analysis.

  • I think relative to my post above I have likely a fatty liver (or aught to?) and think Annie you and I have the same issue. I have a lot of trouble getting to sleep and of course medicating yourself to sleep with wine or booze, just mean you “wake up” at 3 am with anxiety and a racing heart.

  • So Ted no feedback on Kegg pathways and caffeine metabolism?

  • Jonathan Ross

    If it has a half life of around 4-6 hours in the body, that means that in 4-6 hours HALF of the particles have decayed (in Physics terms), that means that it bears no relation to the fact that it affects the body for 4-6 hours.

  • Colin

    Yeah, I don’t think people understand what half-life actually is. The substance can still be active after multiple half-lives have occurred.

  • Ted

    That’s true but the greatest effects of caffeine are experienced in the initial 4-6 hours before half of it has been metabolized. This doesn’t mean that caffeine becomes benign after and yes it does remain active in a person’s system until it is all metabolized.

  • Ted

    Neither the article or my response says that half life equals half of the effect. Not sure why you think that, but the greatest effects of caffeine are experienced by the majority of people in the first 4-6 hours and this isn’t a coincidence but fact.

  • Vicky

    hi, i’m doing a research project for my college course, which involves measuring the participants’ pulse resting pulse rate then again during and after the experiment. My consent form includes a section relating to caffeine consumption and wonder what sort of time lapse would be needed to ensure the pulse is not effected? Would 2 hours be reasonable? thanks in advance 🙂

  • Ted

    Not necessarily, the half-life of caffeine is 4-6 hours so this makes it difficult for you to use people that are caffeine consumers without that also being a variable in your experiment.

  • Victoria Vighetto

    If I had 1,558 mg of caffeine within 7 hours, would it still only take 6 hours to wear off? THANKS for your help! – Victoria

  • Ted

    Hi Victoria, no it would take 4-6 hours for half of the caffeine to be metabolized. After 6 hours there would still be at least 700 mg of caffeine in your system which is more than enough to still cause overdose symptoms.

  • Victoria Vighetto

    Thanks for your response Ted!

  • Anamacio

    What effect would running have on the level of caffeine in my body? Suppose I had 500mg of caffeine in my system and I went out for a 5mi run at 7:30mi pace. So I’d be doing moderate exercise for just over 37min. Would my caffeine levels drop faster than normal? Would the caffeine effects wear off quicker than normal? Because it is 1:24am and I want sleep but i just had a 16oz coffee w/ soymilk/4pumps vanilla from Starbucks at around 9pm and then sipped on a refill from 10pm-11:50pm. And I want to sleep now lol. My eyes are feeling a bit drowzy but Im curious if running will help inactivate or metabolize the caffeine quicker and make it wear out its effects. 🙂

  • Ted

    Exercise can speed up caffeine metabolism slightly, but only on the caffeine that you consumed prior to the exercise.

  • Nancy

    I realize this post is 8 months old, but wanted to respond. I’ve been drinking coffee for years; I quit for a while then go back to drinking it. Sometimes I’d stop drinking it by spreading it out over a week: 1/2 regular coffee + 1/2 decaf; then slowly switch to only decaf, then to no coffee at all. This slow transition was to prevent the coffee withdrawal headaches But then, I tried something different. Instead of coffee, I had a tall glass of fresh green juice about 1/2 hour before breakfast. An hour or two after breakfast I have another glass of green juice, and never get the headache. If a headache comes on mid-day, I have a salad or some other green food. I was surprised how well this worked. If I had a dessert or greasy lunch or dinner, I would get a headache. This lasts about 4 days, and then it is no longer an issue. It appears alkaline foods keep the headache from occurring. Store bought juices have too much sugar. I use about 5 ingredients-an apple, celery, lemon, ginger, and greens ( spinach, kale, collards, or whatever deep green vegetable works for you). The lemon cuts the bitter tastes of strong greens. I use whatever amounts of each ingredient that I want- a 1/2 inch piece of ginger, 3 celery, a bunch of spinach, etc.
    Thanks Ted, this is an informative site.

  • Ted

    You’re welcome Nancy! Thanks for sharing your experience and tip.

Last Modified: November 9, 2017


  • Biology Online
  • Tassaneeyakul, W., Birkett, D. J., McManus, M. E., Tassaneeyakul, W., Veronese, M. E., Andersson, T., ... & Miners, J. O. (1994). Caffeine metabolism by human hepatic cytochromes P450: contributions of 1A2, 2E1 and 3A isoforms. Biochemical pharmacology, 47(10), 1767-1776. Link
  • Grant, D. M., Tang, B. K., & Kalow, W. (1983). Variability in caffeine metabolism. Clinical Pharmacology & Therapeutics, 33(5), 591-602. link
  • Echeverri, D., Montes, F. R., Cabrera, M., Galán, A., & Prieto, A. (2010). Caffeine's vascular mechanisms of action. International journal of vascular medicine, 2010. study link