Multiple peer-reviewed sources, including a 2023 systematic review in PubMed, have documented that caffeine consumption before sleep increases sleep latency—the time it takes to fall asleep. The review quantified this effect, finding that caffeine intake delayed sleep onset by about 9 minutes on average compared to control conditions.
These findings are based on polysomnographic sleep recordings and apply across multiple population groups, though individual sensitivity varies. The same review also reported that caffeine reduced total sleep time by approximately 45 minutes and decreased overall sleep efficiency.
Other reputable sources such as PubMed Central (PMC) and the Sleep Foundation corroborate that caffeine can make it harder to fall asleep, with measurable increases in sleep latency consistently observed in clinical trials.