Caffeine differently affects sleepiness and sleep physiology in rested versus sleep-restricted adolescents.

<title>Abstract</title> <p>Adolescents often experience chronic sleep restriction due to a biologically driven delay in bedtime and early school schedules. Caffeine is widely used to counteract resulting sleepiness, however, its effects on adolescents’ sleep under sleep restriction remain unclear. In this preregistered mixed-design polysomnographic study, 45 adolescents (14–17 years) underwent twice three nights of restricted (6h) or extended (9.5h) sleep opportunity. Three hours before bedtime of the third night, participants received caffeine (2mg/kg) or placebo (double-blinded) in quasi-randomized order. Bayesian analyses indicated that deep sleep intensity (indicated by EEG slow-wave energy) was reduced and sleep architecture disturbed after caffeine compared to placebo, particularly in the beginning of extended nights. Critically, caffeine reduced subjective sleepiness exclusively under sleep restriction and did not affect sleep evaluation in either sleep history. These findings suggest that caffeine's disruptive effects on adolescent sleep are more pronounced and unrecognised during nights of recommended duration than sleep-restricted nights.</p>