Caffeine doesn’t just keep you awake—it disrupts your sleep too.

A 2025 study from Université de Montréal, published in Communications Biology, revealed that consuming caffeine—even just a few hours before bedtime—can increase high-frequency brain activity during sleep. This is especially true for young adults, whose brains are more sensitive to stimulants.

The researchers used EEG monitoring and found that even though participants were technically asleep, their brains remained more active, particularly during slow-wave (deep) sleep. This kind of interference can reduce sleep quality, disrupt memory consolidation, impair recovery, and increase feelings of tiredness the next day—even if total sleep time appears normal. Caffeine affects the adenosine system, which plays a key role in making us feel sleepy and in maintaining deep, restorative sleep.

For better sleep quality, avoid caffeine in the hours leading up to bedtime.