Why do I get jitters from coffee?

Last updated September 3, 2026.

Jitters mean the dose outran your sensitivity. Caffeine blocks the brain's sleepiness signal and raises adrenaline; the FDA lists jitters among too-much symptoms, with anxiety, insomnia, fast heart rate, palpitations, upset stomach, nausea, and headache. Sensitivity and metabolism speed vary widely between people, so there is no universal safe cup count, only the FDA's 400 milligram daily guide for most adults. Empty stomachs, stacked sources like energy drinks, and genetics all lower the threshold. Eat first, downsize, or move to tea; chest pain, irregular heartbeat, or faintness with jitters is a GP matter.

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