It is believed that the sleep-promoting effects of cannabinoids are due to their interactions with cannabinoid receptors in the brain. When cannabinoids bind to these receptors, they send messages to increase levels of sleep-promoting adenosine and suppress the brain’s arousal system. Together, these effects may help cannabis users feel sedated or sleepy.

Cannabis has several different active compounds, including tetrahydrocannabinol (THC) and cannabidiol (CBD). While THC typically acts as a sedative, it can have a stimulating effect for some people, especially for those who are new to using cannabis or taking higher doses. In these cases, using cannabis before bed may result in a longer time falling asleep. CBD appears to promote alertness at lower doses, and sleepiness at higher doses.

Both CBD and THC may also have benefits for chronic conditions that interfere with sleep. However, the effects of the two compounds together may depend on the dose and timing.

In addition to helping you fall asleep faster, cannabis may alter your time spent in the different sleep stages. Short-term cannabis use appears to increase the time you spend in non-rapid eye movement (NREM) sleep, the stages that help you wake up feeling refreshed. However, THC decreases the amount of time you spend in rapid eye movement (REM) sleep, when you spend more time dreaming, processing emotions, and cementing new memories.

Decreasing REM sleep may have some benefits for people with PTSD, since nightmares are a common and disturbing symptom. A study on women with PTSD found that those with more severe PTSD symptoms and poor sleep were more likely to use cannabis to help them cope. One study found that synthetic forms of cannabis significantly decreased nightmares, or stopped them completely, for people with PTSD. Some participants in this study also reported experiencing better overall sleep quality and fewer daytime flashbacks

Over 80% of insomnia patients said that cannabis helps them sleep by relaxing their mind and body. More than half said it helps them sleep more deeply. Another 42% reported it allows them to sleep longer, and 36% reported it allowed them to sleep without waking. When asked about average sleep hours per night, 63% said they get 6-8 hours when only using cannabis, compared to 20% or less saying the same when using sleep medicines combined with cannabis, sleep medications alone, or no sleep aids. 

The survey found that most people prefer to smoke or vape cannabis compared to using oils or edibles. About 79% said they use THC for sleep, more than other forms like CBD or cannabinol (CBN). The majority (82%) said they don’t take any sleep medications currently, though half had used them in the past. People are more likely to use cannabis in place of sleep medications instead of using both at the same time, the study authors noted.

Two recent clinical studies administered small quantities of CBN in multi-cannabinoid formulations.^{28 29} The first, a cross-over randomised controlled trial (RCT) with a 1-week washout, investigated 2-weeks of an oral liquid containing 20 mg THC, 2 mg CBN, and 1 mg CBD in 20 adults with insomnia disorder. The drug significantly improved insomnia disorder symptoms (Insomnia Severity Index (ISI) −5.1 points, p=0.0001, d=0.94) compared with placebo, with no significant changes to polysomnography (measured on night 14 of dosing).²⁸ In an interventional open-label study, current medicinal cannabis users with subjective sleep difficulty reported improved sleep (assessed via an unvalidated subjective survey and a validated non-contact at-home tracking device) after 3-weeks of nightly administration of an oral capsule containing 10 mg THC and 5 mg CBN.²⁹ Importantly, the effects of CBN cannot be disentangled from those of THC in these studies. We are not aware of any clinical studies to-date that have tested the isolated effects of CBN on objectively measured human sleep.

Importantly, a recently published conference abstract reported on a preclinical study in which CBN isolate (10, 30 and 100 mg/kg intraperitoneally compared with zolpidem 10 mg/kg as a positive control) increased the proportion of non-rapid eye movement (NREM) sleep and sleep bout duration 4-hours post administration in Long-Evan rats.³⁰ With the lowest dose, biphasic effects were observed—CBN (10 mg/kg) initially decreased REM sleep proportion; however, 4-hours after administration, a significant increase in the percentage of REM sleep occurred. These results suggest CBN could reduce wake after sleep onset (WASO), given such delayed effects on sleep.