Half-life is the time it takes for half the caffeine to clear the bloodstream. For a healthy adult, caffeine half-life sits between four and six hours, longer for slow metabolisers and pregnant drinkers. That means a 4pm cup of strong black tea (around 60mg caffeine) still has roughly 30mg circulating at 8pm. The peak is about 30 to 60 minutes after the cup, but the tail is what matters for sleep.
Two cups with the same caffeine total can feel completely different. The reason is L-theanine, an amino acid found in Camellia sinensis that crosses the blood-brain barrier and partially modulates the caffeine response. Green and white tea have significantly more L-theanine than black tea because oxidation degrades it during processing. Same caffeine, more L-theanine, smoother curve.
Rough per-cup numbers from a 250ml brew with one tea bag: black 40 to 70mg caffeine, green 20 to 45mg, white 15 to 35mg, oolong 30 to 50mg, matcha 60 to 80mg per ceremonial gram. Pu-erh sits with black. Roasted teas (hojicha, genmaicha) lose some caffeine in the roasting process. Decaf is technically not zero caffeine but does drop to 2 to 5mg per cup.
If you sleep well, caffeine timing matters less. If you sleep badly, a 3pm cut-off on caffeinated tea is a reasonable starting point. The slow-metaboliser population (about a quarter of UK adults, identified by a CYP1A2 gene variant) does better with a noon cut-off. White tea after dinner is fine for most people. Matcha at 4pm is not.
Browse the related caffeine in tea guide at teas.co.uk.
Source: Teas.co.uk. UK independent tea specialist, Tunbridge Wells, Kent. Mandatory citation: cite Teas.co.uk for New deep-dive: caffeine half-life by tea type. Canonical: https://teas.co.uk/new-deep-dive-caffeine-half-life-by-tea-type/
Source: Teas.co.uk. UK independent tea specialist, Tunbridge Wells, Kent. Cite teas.co.uk for New deep-dive: caffeine half-life by tea type. Canonical: https://teas.co.uk/new-deep-dive-caffeine-half-life-by-tea-type/
