The relationship between marijuana and sleep isn't as simple as some have made it out to be.
Though this benefit might appeal to people who have difficulty sleeping, there's an important distinction to consider: not all sleep is restful. The time between closing your eyes for the night and opening them in the morning involves four phases that marijuana use also affects.
The main two phases of sleep — deep (or slow-wave) sleep and REM (rapid eye movement) sleep — are what experts look at when determining the quality of a person's sleep. For daily users, marijuana seems to lengthen the amount of deep sleep time, but it also reduces REM sleep.
Deep sleep is the period when neurons rest and memories from throughout the day are consolidated. For that reason, people suffering from insomnia — which interrupts deep sleep cycles — tend to perform worse on memory tests than those who get a normal amount of deep sleep. That marijuana boosts deep sleep would seem to support its use for individuals with sleep conditions such as insomnia.
But on the other side of the coin, what does cannabis' interruption of REM sleep mean?
It means you're going to dream less — at least in the short run. Some scientists believe that REM sleep "helps regulate body temperature and neurotransmitter levels," Scientific American reported, but even after decades of research into sleep, it's still unclear what this sleep phase actually accomplishes or why it's important. What research has found is that people deprived of REM sleep will naturally make up for it when they do eventually get natural, uninterrupted sleep, according to 2005 study published in the journal Sleep.
Going 30 minutes without REM sleep in one night results in a 35 percent increase in REM sleep the following night, the study found.
Consistent with that finding, anecdotal evidence suggests that marijuana users experience intense, vivid dreams in the week after they quit smoking.