Background: It remains unclear if individuals with Tourette syndrome (TS) or chronic tic disorder (CTD) have an elevated risk of subsequent substance misuse.
Methods: In this population-based cohort study, we investigated the association between ICD diagnoses of TS/CTD and substance misuse outcomes, accounting for psychiatric comorbidity and familial factors. The cohort included all individuals living in Sweden at any time between January 1, 1973, and December 31, 2013. Substance misuse outcomes were defined as an ICD code of substance use-related disorder or cause of death, or as a substance use-related criminal conviction in the nationwide registers.
Results: The cohort included 14,277,199 individuals, of whom 7832 had a TS/CTD diagnosis (76.3% men). TS/CTD was associated with an increased risk of any subsequent substance misuse outcomes (adjusted hazard ratio [aHR], 3.11; 95% confidence interval [CI], 2.94-3.29), including alcohol-related disorder (aHR, 3.45; 95% CI, 3.19-3.72), drug-related disorder (aHR, 6.84; 95% CI, 6.32-7.40), substance-related criminal convictions (aHR, 2.56; 95% CI, 2.36-2.77), and substance-related death (aHR, 2.54; 95% CI, 1.83-3.52). Excluding psychiatric comorbidities had little effect on the magnitude of the associations, with the exception of attention-deficit/hyperactivity disorder, which attenuated the risk of any substance misuse outcomes (aHR, 2.00; 95% CI, 1.82-2.19). The risk of any substance misuse outcomes in individuals with TS/CTD was substantially attenuated but remained significant when compared with their unaffected siblings (aHR, 1.74; 95% CI, 1.53-1.97).
Conclusions: TS/CTD were associated with various types of subsequent substance misuse outcomes, independently of psychiatric comorbidity and familial factors shared between siblings. Screening for drug and alcohol use should become part of the standard clinical routines, particularly in patients with comorbid attention-deficit/hyperactivity disorder.
Keywords: Alcohol; Drugs; Family study; Longitudinal; Tic disorders; Tourette syndrome.
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