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Most caffeine withdrawal eases in 2–9 days, though headaches can last longer if you stop fast after daily use.

Insomnia after quitting caffeine often calms within 1–2 weeks, while some people need up to 3–4 weeks for sleep to feel steady again.

For most adults, 75 mg of caffeine feels strongest for 1–3 hours and can affect sleep for 6–8 hours or longer.

400 mg of caffeine often feels strong for 4–6 hours, but its effects can linger 8–12 hours, especially on sleep.

A 320 mg caffeine dose can affect alertness for 6–12 hours, with sleep disruption possible for longer in some people.

For many adults, 60 mg caffeine feels noticeable for 3–5 hours, yet sleep can still get nudged 6–10 hours later.

46 mg of caffeine often feels noticeable for 2–4 hours, with leftover caffeine in your body for 8–12 hours or longer in slow metabolizers.

Forty mg of caffeine often feels active for 2–4 hours, while small leftovers can linger in your body for 8–10 hours.

A 34 mg caffeine dose often feels active for 2–4 hours, with a quieter tail that can linger 6–10 hours, based on your body and timing.

A 105 mg caffeine dose often feels active for 3–6 hours, and smaller effects can linger for 10+ hours.