Half-life (time to clear half the caffeine) is about 5 h for a typical adult. Smoking speeds it up a lot; the pill roughly doubles it; late pregnancy can triple it; it creeps up with age. Weight barely changes half-life, because a bigger body clears more but also holds more. It does change how concentrated caffeine is, so your sleep line and daily limit scale with weight. Drag the half-life yourself to override.