Caffeine and Sleep
How caffeine blocks the chemical signal of sleep pressure, and how long it lasts.
Last revised
Key takeaways
- Half-life in a typical adult: about 5 hours
- General adult daily limit: 400mg
- Most useful single change: Set a personal cut-off time; early afternoon suits most people.
- Commonest mistake: Assuming falling asleep easily means sleep quality is unaffected.
- See a doctor if any of the signs under "When to get help" below apply to you.
Why it matters
A half-life of about five hours means an afternoon coffee is still measurably present at midnight, whether or not you notice it.
The numbers, in one place
| Measure | Figure |
|---|---|
| Half-life in a typical adult | about 5 hours |
| General adult daily limit | 400mg |
| Recommended limit in pregnancy | 200mg |
| Filter coffee, a mug | 100-150mg |
| Practical cut-off before bed | 8-10 hours for sensitive sleepers |
What helps
- Set a personal cut-off time; early afternoon suits most people
- Count tea, cola, energy drinks and chocolate towards the total
- Reduce gradually over a week or two to limit headaches
- Break the loop of poor sleep and more caffeine at the caffeine end
What to avoid
- Assuming falling asleep easily means sleep quality is unaffected
- Energy drinks to compensate for a sleep debt across consecutive days
- Exceeding 200mg a day in pregnancy
Where to go next
- Making Sense of Caffeine and Sleep
- A Working Checklist for Caffeine and Sleep
- Shift Work and Sleep: Sorting the Evidence From the Noise
- Napping: What Published Guidance Supports
When to get help
See a GP for palpitations, tremor or anxiety that worsens with caffeine, or if you need caffeine to function despite adequate time in bed, which can point to sleep apnoea, anaemia or thyroid problems. Seek urgent advice for an irregular or racing heartbeat that does not settle.
Where this comes from
- European Food Safety Authority — caffeine safety opinion
- NHS — Caffeine in pregnancy
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.