How late can you drink coffee?

What we can tell you today: how thoroughly this has been studied.

Thoroughly studied

7 studies, of which 5 bring together the results of several trials in people. This is as strong as evidence gets.

5 Repeated evidence 5 studies

4 Large controlled trial 1 study

3 Small study in people 1 study

This says how thoroughly something has been studied — not whether it works for you. What each study actually found is in the study itself, and in the plain-language write-ups we are adding.

Appears under: Sleep, energy and the brain · Hair and nails

The studies

5 Repeated evidence The effect of caffeine on subsequent sleep: A systematic review and meta-analysis.
2023 · Sleep medicine reviews
5 Repeated evidence Coffee, caffeine, and sleep: A systematic review of epidemiological studies and randomized controlled trials.
2018 · Sleep medicine reviews
5 Repeated evidence Systematic Review and Meta-analysis of the Effects of Caffeine in Fatigued Shift Workers: Implications for Emergency Medical Services Personnel.
2019 · Prehospital emergency care
5 Repeated evidence Caffeine Supplementation and Hair: A Systematic Review.
2025 · Journal of drugs in dermatology : JDD
5 Repeated evidence Caffeine and neuropsychiatric symptoms in patients with dementia: A systematic review.
2020 · Experimental gerontology
4 Large controlled trial Caffeine selectively mitigates cognitive deficits caused by sleep deprivation.
2021 · Journal of experimental psychology. Learning, memory, a · 276 participants
3 Small study in people Anti-hair loss effect of a shampoo containing caffeine and adenosine.
2024 · Journal of cosmetic dermatology · 77 participants · manufacturer helped fund this