How long does caffeine stay in your system?

If you have been following us on Facebook, you have heard us talk a lot about the health benefits of caffeine and coffee.

And, although there is lots of upside to coffee and caffeine, you probably do not want it in your system all the time.

So, how long does caffeine stay in your system?  Interestingly enough, the answer comes back to your personal genetics.  Awhile back I personally signed up for genetic testing using (which is a super interesting site, by the way), and when I got my results back I was surprised to see that there was a gene that effected caffeine metabolism.


Although the way caffeine works is pretty much the same, bodies metabolize it differently.  Some bodies metabolize caffeine quickly, and others metabolize it slowly.

There is a specific enzyme in our bodies (cytochrome P4501A2, or CYP1A2, for the nerdy among us) that breaks down caffeine so that the body can pee it out.  This enzyme accounts for about 95% of the breaking down of caffeine.  This is what is tied to you being either a fast or slow caffeine metabolizer.

To understand how long caffeine is in your system, you have to appreciate a little bit about how it works.  Once you say, drink one of our coffees, caffeine actually gets into your system pretty quickly, starting to get into your bloodstream in about 5 minutes.


It takes 30 minutes for the full effect of the coffee to hit your body, however.

And, after that?  Well, it depends on how much caffeine you drink, and how quickly your body eliminates it.  It will also determine also whether you get shaky.  Or if you tend to feel adverse effects if you consume too much.


Caffeine does not leave your system all at once.

Caffeine leaves your body based on a half-life.  That half-life is effected by whether you are a fast caffeine metabolizer or a slow caffeine metabolizer.  Caffeine’s half-life in your body will be between 4 and 6 hours, depending on that variable.

So, if you drink 2 cups of coffee, it takes 4 to 6 hours to eliminate half the caffeine.  Your body will still have 1 cup of coffee’s worth of caffeine floating around inside you.

This is why once you start having, say, 8 cups of coffee (or perhaps one of these), that things get tricky.  Lets assume that you are a fast caffeine metabolizer.  This means that your body eliminates half of the consumed caffeine every 4 hours.  And that means 12 hours later you will still have 1 cup of coffee in your bloodstream.

how long does coffee stay in your system?

Or, for slow metabolizers like myself, 18 hours later you will still have 1 cup of coffee in you.

But, it’s still not simple to ask how long does caffeine stay in your system.  Most people do not drink their caffeinated drinks all at once.  Most people sip those drinks over a period of time.  That last cup of coffee at lunch is still a half cup in your system hours later.

Perhaps those of you that consume too much caffeine and that have trouble sleeping at night understand why a little bit better.

So, should you stop drinking coffee?  Of course not.  Just be mindful of the amounts and plan for it throughout the day.  There are actually tons more health benefits than negative health benefits, you just have to moderate it, like anything else in life (and it actually even helps increase the length of your life).

Now that you know this about caffeine and that it is good for you, there are still 2 other surprising things that you should know to be responsible with caffeine consumption, or you might wreck your body.