Abstract
BACKGROUND AND AIMS: Although the co-occurrence of cannabis and depression is well established, less is known about the temporal sequence of cannabis use and depression. The present study had three main aims: to test a symptom-driven pathway in which depression may drive increases in cannabis use, to test a substance-induced pathway in which cannabis use may drive increases in depression and to assess a shared vulnerability model assessing associations between individuals who have (and have not) experienced adverse childhood experiences (ACEs). DESIGN: Data are from an ongoing, longitudinal, cohort study (n = 2234). Data were set up in an accelerated longitudinal design from age 17 to 24 years. SETTING: Initial sample was recruited from Southern California, USA. The majority of participants still live in Southern California. PARTICIPANTS: On average, participants were aged 18 years at wave 8, with more than half identifying as female (54.3%; n = 1350). Most participants identified as Hispanic (1127; 45.4%), followed by non-Hispanic white (510; 20.5%), Asian (503; 20.2%), multi-racial/other (284; 11.4%) and non-Hispanic black (60; 2.2%). MEASUREMENTS: Primary outcomes were past-month days of cannabis use and depression symptoms [patient health questionnaire (PHQ)-8]. The Adverse Childhood Experiences scale was used as our main grouping measure. FINDINGS: In the full sample, we showed that prior levels of depression symptoms were associated with a decrease in cannabis use [opposite to the proposed symptom driven model; B = -0.33 (-0.58, -0.09)]. Dynamic coupling parameters noted individuals who evidenced greater increases in cannabis use between two prior ages reported greater increases in depressive symptoms between subsequent ages [support for a substance-induced pathway; B = 0.53 (0.18, 0.89)]. Similar to the overall sample, for those who had not experienced ACEs, as cannabis use increased we saw a steady increase in depression [support for a substance induced pathway; B = 0.14 (0.04, 0.29)]. However, for those who experienced ACEs, as cannabis use increased we saw a consistent decrease in depression [opposite to the proposed substance-induced pathway; B = -0.18 (-0.28, -0.08)]. CONCLUSION: There is mixed support for both symptom-driven and substance-induced pathways between cannabis use and depression.