A meta-analysis of studies involving more than 3.2 million participants found that major depressive disorder was significantly more prevalent among patients with cannabis use disorder compared to the general population, and vice versa. In a psychiatric sample of individuals with cannabis use disorder, 19% also had current major depressive disorder. This proportion was 22% in the community sample. The paper was published in. Psychiatric Research Journal.
Depression, or major depressive disorder, is one of the most prevalent mental health conditions worldwide. According to recent data, approximately 13% of people have been diagnosed with depression at least once in their life. It is currently estimated that approximately 3% have depressive symptoms severe enough to warrant a diagnosis of depression.
Major depressive disorder is characterized by persistent low mood or loss of interest or enjoyment in most activities. Symptoms may also include changes in sleep, appetite, fatigue, difficulty concentrating, feelings of worthlessness or excessive guilt, and slowness and agitation. More severe cases may include recurring thoughts of death or suicide.
Substance use disorders also tend to be more common in people with depression. A recent large meta-analysis study found that approximately 1 in 4 people with depression also have a substance use disorder. This significantly increases the risk of suicide and contributes to severe social and personal impairment.
Study author Joao Pini Alemar and colleagues point out that cannabis is the most widely used illicit drug around the world. Estimates for 2022 show that approximately 228 million people between the ages of 15 and 64 reported using cannabis in the past year, representing 4% of the world’s population. These authors conducted a meta-analysis aimed at determining how common major depressive disorder is among individuals with cannabis use disorder, and vice versa. They also investigated whether methodological and demographic factors influenced the co-occurrence of these disorders.
The study authors searched scientific databases (PubMed, Google Scholar, and Scientific Electronic Library Online) for studies published in English and Portuguese using keywords such as cannabis, abuse, addiction, depressive disorders, major, and various combinations thereof.
Their search yielded an initial collection of 1,114 studies. After excluding studies that did not meet the criteria, the set was reduced to 55 studies. Of these, 36 were included in meta-analyses investigating the occurrence of major depressive disorder in people with cannabis use disorder, and 18 investigated the occurrence of cannabis use disorder in people with major depressive disorder.
In total, the first study group included 454,547 participants and the second group included 112,328 participants. (There was one additional study with nearly 2 million participants that contributed to the total number of participants but was classified as a clinical population).
Results showed that 22% of individuals with cannabis use disorder in a community sample currently suffered from major depressive disorder. This proportion was 19% in the psychiatric sample.
The lifetime prevalence of major depressive disorder (i.e., whether participants have ever suffered from depression in their life) among individuals with cannabis use disorder was 35% in the psychiatric sample and 32% in the community sample. A psychiatric sample is a group of research participants recruited from a psychiatric facility such as a mental health clinic or hospital, whereas a community sample is a group of research participants recruited from the general population outside of a medical facility.
A meta-analysis of studies examining how common cannabis use disorder occurs in patients with depression found that 28% of psychiatric patients with major depressive disorder currently suffer from cannabis use disorder. In the community sample, this proportion was only 5%. The lifetime prevalence of cannabis use disorder among patients with major depressive disorder was 8% in the psychiatric and 12% in the community sample.
Importantly, the authors highlight significant diagnostic complications when interpreting these high duplication rates. That is, cannabis withdrawal symptoms (such as irritability, anxiety, sleep disturbances, depressed mood, and anhedonia) closely mirror the core symptoms of major depressive disorder. Therefore, when heavy cannabis users abstain, they may be misdiagnosed as depressed when they are actually experiencing acute withdrawal symptoms, potentially inflating the prevalence seen in cross-sectional studies.
“This meta-analysis reveals a high prevalence of MDD (major depressive disorder) in patients with CUD (cannabis use disorder), a significant prevalence of CUD in patients with MDD, and confirms a strong comorbid relationship between the two disorders,” the study authors concluded. “While cannabis use can worsen symptoms of depression, people with MDD are at increased risk of developing CUD. (…) Given the increasing legalization of cannabis and increasing use among young people, this relationship represents a pressing public health concern.”
This study provides important data for scientific understanding of the association between cannabis use disorder and depression. However, this paper reports some numbers that seem counterintuitive, such as the current prevalence of cannabis use disorder in a depressed psychiatric sample being higher than the corresponding lifetime prevalence. The authors note that this is likely due to the small number of studies and the high variability in that particular subgroup. Additionally, the study’s correlational design does not allow definitive causal inferences to be drawn from the results.
The paper, “The Association between Major Depressive Disorder and Cannabis Use Disorder: A Meta-Analysis and Meta-Regression Analysis,” was authored by Joao Pini Alemar, María Olivia Pozzolo Pedro, Kay Leopold, João Vitor Guimarães Mandazi, Ghislaine Koch Jiménez, Israel Kanaan Blaas, Julio Torales, Antonio Ventrilio, and João Mauricio. Castardelli-Maia.
