A new meta-analysis of 55 studies involving more than 3 million people has found that 31% of individuals with cannabis use disorder (CUD) also struggle with major depressive disorder (MDD). While a link between these two conditions has been known for some time, this study provides the clearest evidence to date that the relationship goes both ways. CUD was also found to be present in 10% of those with MDD.
The findings are published in the Journal of Psychiatric Research.
An international team of scientists searched major databases to identify relevant studies published in English and Portuguese through to 2024. They used mathematical models to combine results from millions of people, ensuring they accounted for differences in age, gender, and location.
Setting matters
The team discovered that the overlap between MDD and CUD varies significantly depending on the setting. For example, in the community (among the general public or volunteers in the studies), rates of cannabis use disorder among people with depression are relatively low. However, in psychiatric clinics, the connection is much stronger. More than 28% of patients being treated for depression also meet the criteria for CUD.
The meta-analysis also revealed that the two disorders are often linked throughout a person’s life, even if they are not present at the same time. While 20% of those with cannabis use disorder were found to be depressed at the time they participated in their respective study, 35% had struggled with depression at some point during their lives.
The problem of overlapping symptoms
Despite these findings, the researchers note that several limitations may prevent us from getting a clear picture of what is happening. One major challenge is an overlap in diagnosis where symptoms of cannabis withdrawal, such as anxiety, irritability, and sleep disturbances, are very similar to the clinical signs of depression. This makes it difficult for doctors to determine whether someone is suffering from a depressive disorder or the effects of their cannabis use.
Additionally, much of the data comes from North America, so it may not reflect conditions in other countries or cultures.
Future screening
However, due to the high percentages involved, the study authors recommend that health care providers regularly screen for cannabis use in depressed patients. Likewise, they suggest evaluating depression levels in those seeking help for CUD.
“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,” wrote the team in their paper.
Because the two disorders appear deeply linked, catching one early may prevent the other from worsening.