Caffeine Half-Life: How Long Does Caffeine Actually Stay in the System?

Oh wise and benevolent Trainerroad Hive Mind: I’m still unclear on the concept of Caffeine Half Life. I understand that it takes approximately 4-6 hours (depending) to clear 50% of caffeine from your system, however after that does caffeine metabolize at a constant rate, or following a curve?

For example, if I take 100mg of caffeine at 5am, will I be at 50mg by 10am and 0mg by 3pm…
will I be at 50mg by 10am, 25mg at 3pm, 12.5mg at 8pm, 6.25mg at 1am, etc…

At what point is caffeine completely cleared from my system?

I searched for images of “caffeine half life graph” and got some helpful results. I’m not sure I’d pick just the right graph/study to post here, so give that a go on your search engine of choice.

Good question; seeing those results was helpful for me, too.

I noticed some graphs had different trajectories for typical/average, smoker, on birth control, and maybe others.

Like this (and the same principle applies to any pharmacological compound or drug)

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A good reference: Half Life - StatPearls - NCBI Bookshelf

90% (+/-) of a compound is eliminated in approximately 3-4 half lives and 95% (+/-) after 4-5 half-lives. A general rule is 6-7 half-lives to approach zero. The link given has a nice graph at the bottom (click to expand it).

For caffeine, there is a fairly significant half-life variation between different individuals. Different sources of that variation. Have seen T1/2 estimates in the literature range from 1-10 hours with an average around 4-6 hours. Individuals also have different responses to caffeine which complicates “dosing”. Most people figure out the right dose experimentally for themselves which is a triumph for Personalized Medicine (LOL)

A wonderful molecule. What would we do without it?

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Caffeine follows first order kinetics, which means you have a logarithmic decay in your circulating concentration. Sample graph:

Now, there is some minimal concentration that has to be circulating to have an appreciable pharmacologic effect–the 12.5 mg you’ve got floating around at 8pm likely isn’t doing a whole lot. This threshold (and your half-life) is subject to inter-individual variability.

Not every compound or drug follows first order kinetics. Most notably, ethanol is metabolized by zero order kinetics.

Pharmacokinetics (Deranged Physiology): First order, zero order and non-linear elimination kinetics | Deranged Physiology
Caffeine-specific info: Pharmacology of Caffeine - Caffeine for the Sustainment of Mental Task Performance - NCBI Bookshelf