Cannabis Does Not Improve Sleep: Study Reveals an Unexpected Effect

The findings were published in the journal JAMA Network Open.

The researchers analyzed data from 1,266 participants in the long-running CARDIA study, which began in 1985–1986. In middle age, participants wore wrist-worn sleep monitors for one week and completed questionnaires rating the quality of their rest. This allowed the researchers to compare objective measurements with participants' subjective perceptions.

The results showed that a longer history of cannabis use was associated with poorer objective sleep measures. People with higher cumulative cannabis exposure spent a smaller proportion of the night actually asleep, experienced more frequent awakenings, and had longer periods of wakefulness after initially falling asleep.

Similar patterns were observed among recent cannabis users. Compared with people who had never used cannabis, they were more likely to experience lower sleep efficiency, fragmented sleep, and longer periods of wakefulness during the night. Recent cannabis users were also significantly more likely to sleep for more than eight hours.

However, questionnaire responses showed that cannabis users generally did not rate their sleep quality as poorer. In other words, the disturbances detected by monitoring devices often went unnoticed by the participants themselves.

The association between cannabis use and poorer objective sleep measures persisted even after the researchers accounted for other factors that could affect sleep, including age, sex, race, tobacco smoking, alcohol consumption, physical activity, depression, chronic diseases, and the use of other substances.

Nevertheless, the study does not establish that cannabis directly causes sleep disturbances. The researchers also did not distinguish between different methods of cannabis consumption, such as smoking and eating cannabis-infused products. Participants' habits may also have changed over the decades of follow-up.

To promote healthy sleep, the researchers recommend maintaining a consistent bedtime, keeping the bedroom cool, dark, and quiet, avoiding phones and other screens immediately before bed, and developing a relaxing evening routine. If sleep problems persist, it is advisable to consult a doctor to rule out possible sleep disorders.