Caffeine and Sleep: Half-Life, Timing, and Sleep Architecture Effects
200mg caffeine taken 6h before bed reduces total sleep time by ~1 hour; caffeine half-life is 5–6h via CYP1A2; it blocks A1/A2A adenosine receptors, masking sleep pressure that rebounds upon its clearance.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Sleep loss from 200mg at 6h before bed | ~1 | hour total sleep reduction | Drake 2013; subjects reported this was not disrupting sleep despite objective data |
| Caffeine half-life | 5–6 | hours | Range 3–10h; CYP1A2 enzyme; smokers faster (~3h), pregnant women slower (~9h) |
| Peak plasma caffeine | 30–45 | minutes after ingestion | Well absorbed orally; peak plasma ~2–10 μg/mL from 200mg dose |
| SWS reduction from 200mg caffeine | Significant | reduction | Landolt 2004; slow-wave activity (SWA) in EEG reduced; sleep pressure masked |
| Standard coffee caffeine | 95 | mg per 240ml cup | USDA FoodData Central; range 72–130mg; espresso 63mg/30ml shot |
Caffeine Pharmacokinetics
Caffeine is rapidly and almost completely absorbed after oral ingestion, reaching peak plasma concentrations within 30–45 minutes. It is distributed throughout total body water and crosses the blood-brain barrier freely.
Key pharmacokinetic parameters:
| Parameter | Value |
|---|---|
| Oral bioavailability | ~100% |
| Volume of distribution | 0.6 L/kg |
| Protein binding | 35% |
| Half-life (average) | 5–6 hours |
| Half-life (range) | 3–10 hours |
| Primary enzyme | CYP1A2 |
| Active metabolite | Paraxanthine, theophylline, theobromine |
CYP1A2 is highly polymorphic: “fast metabolizers” (about 50% of people, CYP1A2*1F allele) have half-lives of 3–4 hours; “slow metabolizers” have half-lives of 7–10+ hours. Pregnancy, oral contraceptives, and certain medications slow caffeine metabolism significantly.
The 6-Hour Effect
Drake et al. (2013) tested caffeine timing effects on sleep by giving subjects 400mg of caffeine at 0, 3, or 6 hours before bedtime. All three timing conditions significantly disrupted sleep compared to placebo — even the 6-hour condition reduced total sleep time by approximately 1 hour.
Crucially, subjects in the 6-hour caffeine condition reported not experiencing disrupted sleep despite objective polysomnographic evidence. This demonstrates the same subjective-objective dissociation seen in sleep deprivation research: people may not perceive the sleep disruption caused by caffeine but still experience it and its consequences.
Interaction with Adenosine
Caffeine blocks adenosine A1 and A2A receptors but does not affect adenosine production or accumulation. During the hours of caffeine action:
- Adenosine continues to accumulate normally
- Caffeine prevents adenosine from signaling sleep pressure
- The “crash” occurs when caffeine is metabolized: accumulated adenosine suddenly gains access to all receptors simultaneously, producing intense sleepiness disproportionate to the expected level after caffeine’s duration
This dynamic explains why heavy caffeine users feel disproportionately tired when they stop drinking coffee — adenosine accumulation has continued during caffeine’s masked period, producing a withdrawal-like state.
For connection to other towers: see Coffee Tower caffeine-content page for caffeine levels by brew method, and Matcha Tower EGCG page for L-theanine’s interaction with caffeine.
Related Pages
Sources
- Drake C et al. — Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med (2013)
- Fredholm BB et al. — Actions of caffeine in the brain with special reference to adenosine. Pharmacol Rev (1999)
- Landolt HP et al. — Caffeine attenuates waking and sleeping EEG markers of sleep homeostasis in humans. Neuropsychopharmacology (2004)
- Nehlig A et al. — Caffeine and the central nervous system. Brain Res Rev (1992)
Frequently Asked Questions
What time should you stop drinking caffeine?
For a person with a typical 10pm bedtime and average 5.5h half-life, cutting caffeine at 1–2pm allows 8–9 hours for 75–80% of caffeine to clear. Many sleep researchers recommend a caffeine cutoff of noon–1pm for evening sleepers. Individual variation is large: fast CYP1A2 metabolizers can handle afternoon caffeine better; slow metabolizers (about 10% of people) may be affected by caffeine consumed in the morning.
Does caffeine affect deep sleep?
Yes. Even when caffeine doesn't prevent falling asleep, it reduces slow-wave activity (the EEG measure of deep sleep quality) during the night. Landolt et al. (2004) showed that 200mg caffeine taken in the morning measurably reduced SWA during that night's sleep — demonstrating that caffeine effects persist far beyond waking alertness and impair the restorative quality of sleep even when total sleep time seems normal.