How long does Celsius
stay in your system?

A 12 oz Celsius contains about 200 mg of caffeine, half of the FDA's 400 mg suggested daily ceiling in a single can. Marketed as a fitness and energy drink, it sits at the high end of the energy-drink range, well above a Red Bull or a standard coffee.

From 200 mg, the 5-hour half-life leaves about 100 mg after five hours and 50 mg after ten. Two cans in a day already approach the full daily guidance, so the timing of a second one matters if you want it cleared before sleep.