THC, and cannabis in general, are often reported (anecdotally) to improve sleep. In a survey of Canadians who used cannabis for therapeutic purposes, 85% of people reported using cannabis for sleep, making it the most frequently reported use.[1] Despite this, the research is limited, and the results have been fairly mixed.
THC may improve self-reported sleep quality, including reducing the time to fall asleep (sleep latency) and increasing total sleep time. These effects have been the most notable in people with chronic pain but appear less consistently in other populations.[2][3] However, there seems to be a mismatch between subjective and objective measurements of sleep quality. In studies that have monitored brainwave activity, THC has been found to suppress rapid eye movement (REM) sleep and possibly slow-wave sleep (which is important for memory consolidation) with chronic use, and some studies have found increases in sleep latency rather than the self-reported decreases.[2][4][5]