Substance use disorders and risk for treatment resistant depression: a population‐based, nested case‐control study

BACKGROUND AND AIMS: Treatment‐resistant depression (TRD), defined as inadequate treatment response after at least two adequate treatment trials, is common among patients initiating antidepressant treatment. Current or previous substance use disorders (SUD) are common among patients with depression and often lead to worse treatment outcomes. However, in clinical studies, SUD have not been found to increase the risk for TRD. The aim of this study was to investigate the association between SUD and TRD. DESIGN: Nested case–control study. SETTING: Nation‐wide governmental health‐care registers in Sweden. CASES AND CONTROLS: Data on prescribed drugs and diagnoses from specialized health care were used to establish a prospectively followed cohort of antidepressant initiators with depression (n = 121 669) from 2006 to 2014. Of these, 15 631 patients (13%) were defined as TRD cases, with at least three treatment trials within a single depressive episode. Each case with TRD was matched on socio‐demographic data with five controls with depression. MEASUREMENTS: Crude and adjusted odds ratios (aOR) with 95% confidence intervals (CI) estimated the association between TRD and SUD diagnosis and/or treatment in five different time intervals until the time for fulfillment of TRD definition for the case. The analysis was adjusted for clinical and socio‐demographic covariates. FINDINGS: Having any SUD during, or ≤ 180 days before start of, antidepressant treatment was associated with almost double the risk for TRD [≤ 180 days before: adjusted OR (aOR) = 1.86, CI = 1.70–2.05]. Increased risks for TRD were found ≤ 180 days before treatment start for the subcategories of sedative use (aOR = 2.37; 1.88–2.99), opioids (aOR = 2.02; 1.48–2.75), alcohol (aOR = 1.77; CI = 1.59–1.98) and combined substance use (aOR = 2.31; 1.87–2.99). CONCLUSIONS: Recent or current substance use disorders is positively associated with treatment resistance among patients initiating treatment for depression.