People with cannabis use disorder are more likely to be depressed, study finds

A meta-analysis of studies involving over 3.2 million participants found that major depressive disorder is significantly more prevalent among individuals with cannabis use disorder compared to the general population, and vice versa. In psychiatric samples of individuals with cannabis use disorder, 19% suffered from current major depressive disorder as well. This share was 22% in community samples. The paper was published in the Journal of Psychiatric Research.

Depression, or major depressive disorder, is one of the most prevalent mental health conditions worldwide. Recent data indicate that around 13% of individuals are diagnosed with depression at least once in their lives. Roughly 3% are estimated to currently have depressive symptoms severe enough to justify a diagnosis of depression.

Major depressive disorder is characterized by persistent low mood or a loss of interest and pleasure in most activities. Symptoms also include changes in sleep, appetite, fatigue, difficulty concentrating, feelings of worthlessness or excessive guilt, and slowed or agitated movement. In more severe cases, it can involve recurrent thoughts of death or suicide.

Substance use disorders also tend to be more frequent in depressed individuals. A recent large meta-analytic study found that around 1 out of every 4 depressed individuals suffers from a substance use disorder as well. This substantially increases the risk of suicide and contributes to severe social and individual impairments.

Study author Joao Pini Alemar and his colleagues note that cannabis is the most widely used illicit drug globally. A 2022 estimate stated that approximately 228 million individuals between 15 and 64 years of age reported using cannabis in the past year, accounting for 4% of the global 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 explored whether methodological and demographic factors affect the co-occurrence of these disorders.

Study authors searched scientific publication databases—PubMed (US National Library of Medicine), Google Scholar, and SciELO (Scientific Electronic Library Online)—for studies published in English and Portuguese using keywords such as cannabis, abuse, dependence, depressive disorder, major, and their various combinations.

Their search returned an initial collection of 1,114 studies. After excluding studies that did not meet their criteria, the set was reduced to 55 studies. Of these, 36 were included in a meta-analysis exploring the occurrence of major depressive disorder in individuals with cannabis use disorder, while 18 explored the occurrence of cannabis use disorder in individuals with major depressive disorder.

In total, the first group of studies involved 454,547 individuals, while the second group included 112,328 participants. (One additional study involving nearly 2 million participants contributed to the total participant count but was classified as a clinical population).

The results showed that 22% of individuals with cannabis use disorder in community samples currently suffered from major depressive disorder. This share was 19% in psychiatric samples.

The lifetime prevalence of major depressive disorder (i.e., whether participants had ever suffered from depression in their lives) in individuals with cannabis use disorder was 35% in psychiatric samples and 32% in community samples. Psychiatric samples are groups of study participants recruited from psychiatric settings, such as mental health clinics or hospitals, while community samples are study participants recruited from the general population outside of healthcare institutions.

The meta-analysis of studies looking into how often cannabis use disorder occurs in depressed individuals found that 28% of psychiatric patients with major depressive disorder also suffered from current cannabis use disorder. In community samples, this share was only 5%. The lifetime prevalence of cannabis use disorder among people with major depressive disorder was 8% in psychiatric settings and 12% in community samples.

Importantly, the authors highlight a major diagnostic complication when interpreting these high rates of overlap: the symptoms of cannabis withdrawal (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 with depression when they are actually experiencing acute withdrawal, potentially inflating the prevalence rates seen in cross-sectional studies.

“This meta-analysis reveals a high prevalence of MDD [major depressive disorder] among individuals with CUD [cannabis use disorder] and a significant prevalence of CUD among individuals with MDD, confirming a strong comorbid relationship between the two disorders,” the study authors concluded. “Cannabis use may exacerbate depressive symptoms, while individuals with MDD are at an increased risk of developing CUD. […] Given the growing legalization of cannabis and its rising use among younger populations, this relationship represents a pressing public health concern.”

The study contributes vital data to the scientific understanding of the links between cannabis use disorder and depression. However, the paper reports some figures that appear counterintuitive, such as the current prevalence of cannabis use disorder among depressed psychiatric samples being higher than the corresponding lifetime prevalence. The authors note this is likely due to the small number of studies and high variability in that specific subgroup. Additionally, the correlational design of the study does not allow for definitive causal inferences to be derived 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, Maria Olivia Pozzolo Pedro, Kae Leopoldo, Joao Vitor Guimaraes Mandaji, Gislaine Koch Gimenes, Israel Kanaan Blaas, Julio Torales, Antonio Ventriglio, and Joao Mauricio Castaldelli-Maia.