How do caffeine and other stimulants influence sleep?

• A. They increase sleep latency and reduce sleep efficiency; they suppress slow-wave and REM sleep; long half-lives prolong effects.
• B. They improve sleep quality and increase REM sleep.
• C. They have no effect on sleep stages.
• D. They only affect wakefulness but not sleep architecture.

Answer: (A)

Stimulants like caffeine disrupt sleep by increasing brain arousal through blocking adenosine, a chemical that promotes sleep. This makes you take longer to fall asleep, so sleep onset latency goes up. Once you do sleep, the sleep tends to be less efficient—there’s more time awake in bed and more interruptions—so overall sleep efficiency drops. They also blunt key sleep stages: slow-wave sleep (the deepest, most restorative part of sleep) and REM sleep (important for memory and mood) are reduced. The lingering effects depend on the substance’s half-life; caffeine, for example, stays in the system for hours, so the stimulant effect can spill into the night, prolonging wakefulness and further disrupting sleep architecture. These effects are not compatible with improved sleep and they are consistent with how stimulants influence sleep stages.