Attention Deficit/Hyperactivity Disorder and risk for non-affective psychotic disorder: The role of ADHD medication and comorbidity, and sibling comparison.

Attention Deficit/Hyperactivity Disorder (ADHD) is the most common psychiatric disorder in childhood. It is unclear whether ADHD increases the risk of non-affective psychotic disorder (NAPD). The study included a matched cohort, drawn from all born in Sweden 1987-1991 (n = 548,852). ADHD was defined as ICD diagnosis and/or prescription of ADHD medication. We distinguished between stimulants and non-stimulants, and usage duration (<1 year, 1-2 years and ≥2 years). We calculated odds ratios (OR) with 95% confidence intervals (CI) for NAPD, adjusted for confounders, comorbid autism spectrum disorder (ASD) and substance abuse. ADHD cases were also compared to their unaffected full siblings. We analyzed 18,139 ADHD cases and 72,437 sex and birth year matched controls. NAPD was more common in cases than controls (2.7 and 0.4%, respectively). After adjustment for confounders, ADHD cases had markedly high risk for NAPD (OR: 6.99; 95% CI 6.03-8.10), which attenuated further after adjustment for ASD and substance abuse (OR: 2.57; 95% CI 2.09-3.16). Utilization of ADHD medication increased the risk for NAPD (ORs for change in odds of NAPD for every 5 extra prescriptions of stimulants 1.06 (95% CI 1.02-1.10) and, non-stimulants 1.15 (95% CI 1.01-1.30)). There was no association between usage length of medication and risk for NAPD. The risk was higher in individuals with ADHD than their unaffected siblings (OR: 2.95 (95% CI 2.07-4.20)). Overall, ADHD was associated with elevated risk for NAPD, which is not entirely explained by shared familial factors. The clinical severity leading to medical treatment may also increase NAPD risk. Ethics approval: Approved by the ethical committee in Stockholm, Sweden (dnrs: 2010-1185-31/5 and 2013/1118-32).