Which substance is known to predominantly inhibit REM sleep?

Alcohol is known to predominantly inhibit REM sleep due to its sedative properties. While it may initially facilitate the onset of sleep and increase the duration of non-REM phases, it tends to suppress REM sleep throughout the night. This affects sleep architecture, leading to disrupted and less restorative sleep patterns. After the body metabolizes alcohol, there can be a rebound effect resulting in fragmented sleep, making the suppressive impact on REM sleep particularly noticeable.

In contrast, melatonin primarily plays a role in regulating sleep-wake cycles but does not inhibit REM sleep. Caffeine is a stimulant that can delay the onset of sleep but does not have a direct inhibitory effect on REM sleep. Nicotine can disrupt sleep patterns as well but is not specifically known for inhibiting REM sleep to the extent that alcohol does.