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.

Get Help Quitting Caffeine

Reduce your caffeine intake without pain and discomfort.

See our new 10-step plan
  • Melanie Phares

    I know adenosine builds up throughout the day as a by product of ATP metabolism and your highest levels are in the evening, contributing to the sleep cycle. But what happens to the adenosine over night to cause levels to drop?


  • Ted

    During sleep adenosine levels drop but I’m not sure by which mechanism this occurs.

  • Mark Faine

    Is there something you can ingest that will speed the metabolism of caffeine? I’m hypersensitive, so I can have 200mg of caffeine at 7am and still be wide awake at 2 am. It would be good if I could find an “antidote.”

  • Ted
  • Logic

    Antidote: Drink less caffeine. At roughly a 6 hour halflife, 200 mg of caffeine at 7 would mean approximately 100mg at 1pm, 50mg at 7pm, and 25mg at 1am. Don’t underestimate these levels in your system. The problem you have makes me think of how a person can overdrink and still be drunk by the next morning because their liver has yet to process the remaining alcohol in the body. They may ask for a cure or a way to speed up how their body processes alcohol, but the answer is still: drink less of the stimulant/depressant.

  • Mark Faine

    Yeah, but 200mg is just a single cup of coffee.

  • Mark Faine

    I bought it. Tried it last Saturday. It doesn’t work. No difference at all.

  • Ted

    I guess if you lack much the mechanism in the liver to process caffeine well, the herb has nothing to speed up. You should get your money back.

  • bm3520

    For a given level of caffeine, is the type of experience – jittery, focused, hyper, calm but alert, etc – affected by the delivery system? In other words do different methods of intake – gum, coffee, tea, energy drinks, etc – affect the way the caffeine is experienced, the “high”?

  • Ted

    To an extent. The rate at which it is consumed and therefore absorbed affects the perceived effects.

  • Elliott Krejci

    It is safe for me to drink 300mg of caffeine. So if I drink 300mg of caffeine at 7:30am, at 1:30pm it would be at 150mg. So could I drink another 150mg with no “adverse” effects?

  • Jordan Moore

    Correct! Assuming your body metabolizes at a rate of 150mg/6hrs, everyone is different. As you build your tolerance to caffeine (up regulation of adenosine receptors and increased phosphodiesterase enzymes in the body), you will need larger amounts of caffeine to fill those new entities. Caffeine not only helps activate your sympathetic nervous system but keeps it there once it has been activated so personally if you’re a person of high stress or at risk for a heart attack I’d avoid high levels of caffeine.

  • Spencer J McGill

    So how does it work with tolerance ? So let’s say I drink a cup of coffee now, at 8 pm… I want to go to bed at 12 .. I have a high tolerance. The caffeine still hasn’t worn off but I’ll be able to sleep… Because the effects have worn off… And why the crash?. How about drinking and then drinking alcohol which has the opposite effect… Do they cancel each other?

  • jake

    I seem to have had an increase in sensitivity to caffeine after consuming greater quantities too. Can you point me in the direction of more information on this subject?

  • Ted

    Sure, Jake. Here’s another article of ours

  • Chris Grey

    Very interesting reading. As a non-caffeine taker I wonder how long it takes to actually feel the effects. I always order decaffeinated coffee but occasionally they try to slip in ordinary coffee. I can tell before the end of the cup that I have taken caffeine, I think. I am told that this cannot be true and it must be psychosomatic. But how would that be the case if I do not know that the coffee isn’t decaffeinated?

  • Ted

    It takes about 45 minutes for all of the caffeine to be absorbed but you can generally start feeling the effects within 10-15 minutes, so seems pretty logical that you can tell when you’ve been slipped a regular. It irritates me when servers or workers are so blase’ about making sure a person gets their decaf. Some people can have serious reactions to caffeine.

  • Kyla Fite

    Okay so if I took 300mg of caffeine at 8am and another 300mg at 1:30pm. Is that enough to cause an overdose? What do you do about an overdose? Dizziness, and just an over all fuzzy feeling.

  • Magnus Hansen rona

    The sugested intake is around 400-500 mg but you should be fine with up to 5 grams in your body at once, but you shouldnt take that amount ofcourse.

  • vikktoria gray

    you need 80-100 cups of coffee a day or 150-200mg/ kg of body mass

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