Cannabis use disorder has been strongly linked with major depressive disorder in a new review of existing research.
It remains unclear why this link exists.
Could cannabis use disorder be driving depression, or are people with depression self-medicating with cannabis?
There may even be shared risk factors underpinning both conditions. While these two conditions are known to occur together, more data is needed on their relationship.
The international team of researchers conducted a global review of the evidence to date, in light of cannabis becoming legalized in some parts of the world.
The review covered 55 previous studies involving more than 3.2 million people, including nearly half a million with cannabis use disorder (CUD) and more than 100,000 with major depressive disorder (MDD).
They evaluated the prevalence of MDD rates within the CUD population and vice versa, finding that depression seems to increase the likelihood of cannabis use, and cannabis use seems to raise the risk of depression.
It’s worth noting that medical cannabis is sometimes prescribed for MDD in some US states.
The researchers found that almost 32 percent of people with CUD also had MDD, while CUD was also reported by a little over 10 percent of people with MDD.
That’s considerably higher than the prevalence of either condition in the general population.
In a subgroup analysis, the researchers found that the two conditions may be linked even when they do not occur simultaneously.
“Overall, these findings indicate that MDD is common across all subgroups of individuals with CUD, with particularly elevated rates in psychiatric settings and when using lifetime diagnostic criteria,” the team writes.
“Differences between psychiatric and community samples – especially the markedly higher current CUD prevalence in patients with MDD – underscore the need for systematic screening across treatment settings.”
The findings do not prove that one condition causes the other: the review was not designed to prove cause and effect. It pooled existing studies rather than following one new group of people over time.
Though there’s a strong association, we can’t say for sure that MDD is causing CUD, or vice versa, and even with further research, cannabis use and depression could be difficult to untangle in real life. For example, cannabis withdrawal can cause outward signs similar to the symptoms of depression, including anxiety and problems with sleep.
What we can say is that the review encompasses a large dataset, and gives us our most comprehensive look to date at how the overuse of cannabis and serious, persistent depression are connected.
Cannabis has previously been linked to gene expression changes and an increased risk of heart disease, while depression is connected to serious diseases and dementia risk.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>Cannabis use disorder refers to a problematic pattern of cannabis use that can involve cravings, withdrawal, increased tolerance, and difficulty cutting down despite negative consequences.
Major depressive disorder is marked by persistent low mood or loss of interest, along with symptoms such as sleep disruption, fatigue, and poor concentration.
The hope is that by better understanding the link between these conditions, they can be managed and treated appropriately.
The researchers say this is clinically important because, in people with both disorders, one condition could be overlooked or receive less attention when the other is already being treated.
Related: Some Signs of Depression May Show Up in Blood, Study Finds
“These findings emphasize the importance of addressing both conditions concurrently in clinical and research settings,” write the review authors.
“While pharmacological treatments for comorbid CUD and MDD remain inconclusive, psychological interventions such as cognitive behavioral therapy and motivational interviewing show promise and warrant further investigation.”
The research has been published in The Journal of Psychiatric Research.
