In short
- In healthy adults, caffeine's half-life is about 5 hours on average, but it ranges from about 2 to 10 hours between people.
- So half of a 2 pm coffee can still be in your body at 7 pm, and a quarter at midnight.
- In one study, 400 mg taken 6 hours before bed still cut sleep by about an hour.
- Official guidance: up to 400 mg a day for most adults, and 200 mg a day in pregnancy. Count every source.
What caffeine actually does
From the moment you wake, a chemical called adenosine slowly builds up in the brain. The longer you are awake, the more there is. This build-up is called "sleep pressure", and it is one of the two main forces behind sleep. The other is your body clock.
Caffeine has a similar shape to adenosine and sits in the same receptors, blocking them. The adenosine is still there. Caffeine just stops the brain from reading it. When the caffeine clears, the built-up sleep pressure is still waiting.
What "half-life" means
Half-life is the time it takes your body to clear half of a substance. For caffeine in healthy adults it averages about 5 hours. The liver does most of the work, and the speed varies a lot:
- Slower: pregnancy (especially later on), the contraceptive pill, some medicines, liver problems, and certain genes.
- Faster: smoking roughly halves the half-life.
The maths, for a typical person
Take a 100 mg coffee at different times and assume a 5-hour half-life:
| Coffee at | Left at 10 pm | Left at midnight |
|---|---|---|
| 8 am | about 14 mg | about 11 mg |
| 12 noon | about 25 mg | about 19 mg |
| 2 pm | about 33 mg | about 25 mg |
| 5 pm | about 50 mg | about 38 mg |
For a slow metaboliser, with a half-life closer to 8 hours, a 5 pm coffee would still leave more than half at 10 pm.
What the research found
In a well-known study, adults took 400 mg of caffeine (roughly 3 to 4 mugs of filter coffee) at bedtime, 3 hours before, or 6 hours before. Even at 6 hours, sleep measured at home was about an hour shorter. Many people did not notice the change themselves.
How much is in what?
Typical amounts, based on UK Food Standards Agency figures. Real amounts vary by brand and brew.
| Drink or food | Caffeine |
|---|---|
| Mug of filter coffee | about 140 mg |
| Mug of instant coffee | about 100 mg |
| Mug of tea | about 75 mg |
| Can of energy drink (250 ml) | about 80 mg |
| Can of cola | about 40 mg |
| 50 g bar of plain chocolate | under 25 mg |
| NOVR Morning, one serving | 75 mg |
| NOVR Social, one serving | 50 mg |
How much is too much?
The European Food Safety Authority concluded that, for healthy adults, up to 400 mg a day from all sources raises no safety concerns, and single doses of up to 200 mg are fine. In pregnancy the NHS advises no more than 200 mg a day. Children and people sensitive to caffeine should have less. Supplements count towards the total, so add up coffee, tea, energy drinks and supplements together.
How we use this at NOVR
- Morning (75 mg) is made to sit alongside your usual coffee, not replace it, so check your daily total. We say take it before 2 pm.
- Social (50 mg) is the one planned exception for an evening out. We say take it at least 4 hours before bed, and not every night.
- Night contains no caffeine.
A cut-off is a habit, not a law. If you are a slow metaboliser, or your sleep is easily disturbed, an earlier cut-off may suit you better.
Sources
- Drake C et al. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med 2013;9:1195–200. doi:10.5664/jcsm.3170
- EFSA NDA Panel. Scientific opinion on the safety of caffeine. EFSA Journal 2015;13(5):4102. doi:10.2903/j.efsa.2015.4102
- Institute of Medicine (US). Caffeine for the Sustainment of Mental Task Performance, Appendix B: Pharmacology of caffeine. National Academies Press, 2001.
- Food Standards Agency. Caffeine and pregnancy / high-caffeine drinks guidance. food.gov.uk
- NHS. Foods to avoid in pregnancy: caffeine. nhs.uk
This article is general education, not medical advice. Listing a study describes the research only. It is not a claim that NOVR has the same effect.