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… OR
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?
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?
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.