Several hypotheses may explain the association between substance use, posttraumatic stress disorder (PTSD), and depression. However, few studies have utilized a large multisite dataset to understand this complex relationship. Our study assessed the relationship between alcohol and cannabis use trajectories and PTSD and depression symptoms across 3 months in recently trauma-exposed civilians.

In total, 1618 (1037 female) participants provided self-report data on past 30-day alcohol and cannabis use and PTSD and depression symptoms during their emergency department (baseline) visit. We reassessed participant's substance use and clinical symptoms 2, 8, and 12 weeks posttrauma. Latent class mixture modeling determined alcohol and cannabis use trajectories in the sample. Changes in PTSD and depression symptoms were assessed across alcohol and cannabis use trajectories via a mixed-model repeated-measures analysis of variance.

Three trajectory classes (low, high, increasing use) provided the best model fit for alcohol and cannabis use. The low alcohol use class exhibited lower PTSD symptoms at baseline than the high use class; the low cannabis use class exhibited lower PTSD and depression symptoms at baseline than the high and increasing use classes; these symptoms greatly increased at week 8 and declined at week 12. Participants who already use alcohol and cannabis exhibited greater PTSD and depression symptoms at baseline that increased at week 8 with a decrease in symptoms at week 12.

Our findings suggest that alcohol and cannabis use trajectories are associated with the intensity of posttrauma psychopathology. These findings could potentially inform the timing of therapeutic strategies.

Prospective population-based studies of psychiatric comorbidity following trauma and severe stress exposure in children are limited.

To examine incident psychiatric comorbidity following stress disorder diagnoses in Danish school-aged children using Danish national healthcare system registries.

Children (6–15 years of age) with a severe stress or adjustment disorder (ICD-10) between 1995 and 2011 (n = 11 292) were followed prospectively for an average of 5.8 years. Incident depressive, anxiety and behavioural disorder diagnoses were examined relative to an age- and gender-matched comparison cohort (n = 56 460) using Cox proportional hazards regression models. Effect modification by gender was examined through stratified analyses.

All severe stress and adjustment disorder diagnoses were associated with increased rates for all incident outcome disorders relative to the comparison cohort. For instance, adjustment disorders were associated with higher rates of incident depressive (rate ratio RR = 6.8; 95% CI 6.0–7.7), anxiety (RR = 5.3; 95% CI 4.5–6.4), and behavioural disorders (RR = 7.9; 95% CI 6.6–9.3). Similarly, PTSD was also associated with higher rates of depressive (RR = 7.4; 95% CI 4.2–13), anxiety (RR = 7.1; 95% CI 3.5–14) and behavioural disorder (RR = 4.9; 95% CI 2.3–11) diagnoses. There was no evidence of gender-related differences.

Stress disorders varying in symptom constellation and severity are associated with a range of incident psychiatric disorders in children. Transdiagnostic assessments within a longitudinal framework are needed to characterise the course of post-trauma or severe stressor psychopathology.