(WEBMD) - Think a nightcap may help you get a better night’s sleep? Think again. A new review of 27 studies shows that alcohol does not improve sleep quality. According to the findings, alcohol does allow healthy people to fall asleep quicker and sleep more deeply for a while, but it reduces rapid eye movement (REM) sleep. And the more you drink before bed, the more pronounced these effects. REM sleep happens about 90 minutes after we fall asleep. It's the stage of sleep when people dream, and it's thought to be restorative. Disruptions in REM sleep may cause daytime drowsiness, poor concentration, and rob you of needed ZZZs.