The dose rule
Which can, when — for your night, not ours.
The cans are dosed for a shift that ends at 07:00 and a bed at 08:00, in a body that clears caffeine with a five-hour half-life. If that is not your night, put yours in. The chart and the numbers come from the same model that dosed the cans.
Drink the 03:00 can
- it leaves at bedtime
- —
- in you at bedtime, all cans
- —
- glasses of çay
- —
- peak
- —
Five hours is a typical half-life for a healthy adult. It is shorter in smokers and much longer in pregnancy, with some oral contraceptives and with liver conditions — up to twice as long, or more. This is a model of a typical body, not advice about yours.
How the doses were chosen
One rule, run backwards.
Decide what should be left at bedtime; work out how much caffeine at each hour leaves exactly that; round it. The rule is 20 mg at 08:00 — one glass of çay.
The model is the one pharmacologists use for a drink: absorbed quickly (half in nine minutes), cleared slowly (half in five hours). In a formula, the amount in the body τ hours after drinking a dose D is
A(τ) = D · ka / (ka − ke) · (e−keτ − e−kaτ)
with k = ln 2 divided by each half-life. Set A = 20 mg at 08:00, solve for D at each hour, round to 10:
| can | hours to 08:00 | rule says, mg | in the can | left at 08:00 |
|---|---|---|---|---|
| 22:00 Vişne | 10.0 h | 77.6 | 80 | 20.6 |
| 01:00 Limon & Zencefil | 7.0 h | 51.2 | 50 | 19.5 |
| 03:00 Kara Dut | 5.0 h | 38.8 | 40 | 20.6 |
| 05:00 Nane & Misket Limonu | 3.0 h | 29.4 | 30 | 20.4 |
The rounding is why the cans leave 19.5 to 20.6 mg rather than exactly 20. The 07:00 can is not on the table: an hour before bed, the rule would allow 26 mg, and we would rather it were none.
Limits
The numbers that are not ours.
And the one that matters most after a night shift: caffeine moves tiredness later, it does not remove it. If you are too tired to drive home, a can will not make you safe to.