The half-life of caffeine
![The half-life of caffeine illustration: showing the effect of caffeine rising then decreasing over time](https://images.prismic.io/sketchplanations/ec7c46c4-3de7-4a91-87a6-7b1647a9ccd6_153511487793.jpg?auto=compress%2Cformat&fit=max&w=3840&q=50)
The half-life of caffeine is about 4 hours.
The data vary, but for a medium-sized adult, you can probably expect half of the caffeine from that 3 pm cup of coffee to still be doing half of its thing about 7 pm, 4 hours later. Apparently, smokers deal with caffeine quicker, and caffeine sticks around in children much longer.
You can expect about 10 minutes before it first kicks in, which, I suppose, is why if you’re feeling tired while driving, it’s a decent plan to take a break and drink a coffee, then have a 15-minute nap. See tiredness can kill, take a break. Once it starts to kick in, you might hit peak caffeine any time from 45 minutes to 2 hours later.
Caveat: The chart visualisation is extrapolated from reported data, so the shape is only approximate.
Some references say longer, and some say from 3-9 hours or so. My source, which seemed pretty comprehensive, was:
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