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Caffeine cutoff and alcohol (sleep)

In controlled studies of healthy adults, caffeine taken in the hours before bed shortened and lightened night-time sleep, and the effect was still present when caffeine was taken six or more hours before bedtime. Alcohol before bed shortens the time taken to fall asleep and deepens early-night sleep, but delays and reduces REM sleep and disturbs the second half of the night, with REM effects seen from about two standard drinks. In adults prone to snoring or obstructive sleep apnoea, alcohol is associated with more breathing events and lower oxygen levels during sleep.

  • Energy
  • Sleep

Evidence retrieved up to

What the research shows

In healthy adults, caffeine taken within several hours of bedtime reduces subsequent sleep, and a moderate-to-large dose still disrupted sleep when taken six hours before bed; a meta-analysis estimated that a cup of coffee needs to be taken about nine hours before bedtime to avoid a reduction in total sleep time.

Moderate certaintyFurther research may change the size of the effect.
No known concerns at usual amountsRisk

Who this is about

healthy adults

Practical note

Graded moderate: controlled trials pooled in a 2023 meta-analysis of 24 studies plus a placebo-controlled home study; downgraded once for imprecision of the cutoff, which is a model estimate from small studies. The meta-analysis estimated 8.8 hours for coffee (107 mg per 250 mL) and 13.2 hours for a pre-workout supplement serve (217.5 mg); the home study used 400 mg at 0, 3 and 6 hours before bed. Sensitivity to caffeine varies between people.

Vegan note

Caffeine sources such as coffee, tea, cola, energy drinks and pre-workout products are typically plant-derived; the findings apply regardless of diet.

Sources

In healthy adults, caffeine before sleep reduces total sleep time and sleep efficiency, lengthens the time taken to fall asleep and time awake during the night, and shifts sleep from deep sleep towards light sleep.

Moderate certaintyFurther research may change the size of the effect.
No known concerns at usual amountsRisk

Who this is about

healthy adults

Practical note

Graded moderate: a 2023 meta-analysis of 24 controlled studies found total sleep time down by 45 minutes, sleep efficiency down by 7%, sleep onset latency up by 9 minutes, wake after sleep onset up by 12 minutes and deep sleep down by 11.4 minutes; downgraded once because the included studies were small and varied in dose and timing.

Sources

In healthy adults, alcohol before bed shortens the time taken to fall asleep and consolidates the first half of the night, but increases sleep disruption in the second half of the night.

Low certaintyFurther research is likely to change this.
Take care: see the safety noteRisk

Who this is about

healthy adults

Practical note

Graded low: consistent laboratory findings in healthy volunteers, but the source is a qualitative review without pooling, and a later meta-analysis found large uncertainty for total sleep time, sleep efficiency and wake after sleep onset, and saw faster sleep onset and quicker entry to deep sleep only at high doses (about five standard drinks).

Vegan note

Some wines and beers are clarified with animal-derived fining agents; this does not change the sleep findings.

Safety note

Alcohol carries health risks beyond sleep; these studies give no support for drinking to aid sleep.

Sources

In healthy adults, alcohol before bed delays the first period of REM sleep and reduces the amount of REM sleep, with REM disruption seen from a low dose of about two standard drinks and worsening as the dose rises.

Moderate certaintyFurther research may change the size of the effect.
Take care: see the safety noteRisk

Who this is about

healthy adults

Practical note

Graded moderate: a 2025 meta-analysis of 27 studies in healthy adults found a dose-response relationship, consistent with an earlier qualitative review; downgraded once for indirectness, as most studies were short laboratory protocols. The meta-analysis defined a low dose as up to 0.50 g per kg (about two standard drinks) and a high dose as from 0.85 g per kg (about five).

Safety note

Alcohol carries health risks beyond sleep; these studies give no support for drinking to aid sleep.

Sources

In adults susceptible to snoring and obstructive sleep apnoea, alcohol consumption is associated with more severe snoring, more breathing events per hour of sleep and lower oxygen saturation during sleep.

Low certaintyFurther research is likely to change this.
Caution: see the safety noteRisk

Who this is about

adults susceptible to snoring and obstructive sleep apnoea

Practical note

Graded low: a 2020 meta-analysis of 13 polysomnography studies (279 patients) found the apnoea-hypopnoea index higher by 3.98 events per hour and lowest oxygen saturation lower by 2.72 percentage points with alcohol; downgraded for small total sample and mixed study designs.

Safety note

Adults who snore heavily or live with obstructive sleep apnoea are the group in which alcohol was linked to worse breathing during sleep; discussing alcohol with a clinician is reasonable for this group.

Sources