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

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  • Ted

    You may want to go back and study your biology textbooks. Sublingual and oral absorption is well known and documented. You are correct that macronutrients wouldn’t be absorbed in this way, but certain micronutrients like B vitamins; and drugs including caffeine and nicotine definitely do. The later two wouldn’t be considered “nutrients” at all.

  • haha

    I cant even drink caffeine anymore 🙁 It makes me shaky, dizzy, heart race, and sometimes sick to my stomach. Really sucks. If I want a soda I’m usually limited to Sprite or buying caffeine free Pepsi or Mountain Dew. Why would it effect me so? I used to be able to drink it all the time with no effect….

  • coffee tryhard

    I also can only have caffeine in the morning, it keeps me awake for about 8 hours, as i found out one night! its so depressing, i always feel like it in the afternoon

  • HELLO!

    Soy milk? Half and half is going to be infinitely better for you.

  • Lou

    Caffeine is used for energy and to wake people up? Are you being serious? I’m laughing my butt off at you!

  • Karl Davis

    I hate coffee, but I’ve read that caffeine can prevent Alzheimer’s. It seems the effects are very potent, and this conclusion is backed by official places like the NIH, not alternative or pseudoscience places. The idea of taking caffeine pills for 30 years with this goal sounds extreme. Any thoughts?

  • Gub

    Replying two years later! Apparently, because of the way caffeine works, it’s actually easier for the body to go to sleep for about the first 20-30 minutes of the brain caffeination process. Once you are asleep, caffeine has no effect. Some theorise that caffeine could actually be used as a sleep aid if taken with superb timing.

  • Ted

    Coffee would be your best bet. Caffeine pills do not deliver all the antioxidants that coffee does. From other research, these antioxidants have a lot of health promoting benefits.

  • Mark Bell

    The Alzheimer’s benefits may be related to improved fat metabolism instead of glucose/glycogen. There are suggestions a higher fat diet can benefit brain disorders (the brain is mostly fat, after all) and coffee does stimulate fat burning. No definite answers yet, but interesting correlations …

  • Adam M

    I can drink 4 cups of strong coffee and not feel any effects. I think I’m a freak when it comes to drugs…

  • Ronnie

    Yes! I have found that if I drink “too much” coffee in the evening… I sleep like a baby! But if I drink “just enough”, up for many hours past bed time!

  • yrome

    Is the half life of caffeine in the bloodstream increase by the amount of coffee consumed ??? If the half life of a 7 oz cup takes 2.5 – 4 hrs; would that time increase if say, 4 cups were consumed ???

  • Ted

    You have to figure half life by milligrams of caffeine.

    Lets say that 4 cups equals 400mg

    After 4 hours 200mg remains

    After 4 more hours 100mg remains

    After 4 more hours 50mg remains and so on.

    This can be faster or slower for different people and the caffeine amounts will effect people differently based on their built up tolerance/ sensitivity.

  • yrome

    To ensure that I’m understanding you I submit this; there could possible be as much 200mg in one’s body depending on the amount consumed…..also, does years of consumption factor into the equation ???

  • Ted

    Yes and years of consumption would only factor into the perceived and physiological effects of the caffeine not the metabolism of the caffeine.

  • yrome

    Thanks Ted for your expertise…..I’ve asked these questions as I don’t believe what my medical provider says when she says I’m a diabetic…..I was never advised to refrain from coffee beyond the NPO instructions. As a huge coffee drinker, as well as a alcohol consumer even while consuming coffee… research indicates that these two drinks can, and most likely had an adverse, increase affect on my high fbs results. While there are siblings (4 sisters) with diabetes, I demonstrate no symptoms; no effects other than the blood glucose. Furthermore, these results were obtained with faulty instructions at best, as I consumed these drinks with the NPO instructions, not with the 24 hour instructions I later discovered I needed to observe. It is my belief that with proper, correct adherence to guidelines prior to the blood drawing, the results will be normal. As a former, retired medical professional; giving instructions to patients for PET Imaging, perhaps its time that I choose another provider. Thanks for your shoulder !!!

  • Ted

    No worries, I’m glad we could help. Let us know if your next results are better as I’d be curious.

  • Marcea Garibay

    I have a cup of warm coffee and get really groggy almost right away… I wish it kept me awake… However apple juice does help me stay awake

  • wayno1955

    Ted, since coffee (caffine) is also a diuretic, when can I take a vitamin suppliment after drinking my usual three cups of coffee in the morning? I am concerned the vitamins taken will also exit my body after consuming coffee.
    Is there a time frame that makes it safe for taking vitamins so they are absorbed in the body and not exited out with everything else? Thanks!

  • Ted

    Caffeine does have diuretic properties, but when taken in the form of coffee it creates neither negative nor positive hydration. Also people build up tolerance to this effect as well. However, I remember when I drank coffee daily, I did pee a lot more so there could be more to this than what the research says. I think taking your supplements at lunchtime would probably be a safe bet.

Last Modified: November 9, 2017


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