ObjectiveWe aimed at determining whether gender modified associations between ADHD and psychiatric comorbidities in adults.MethodWe identified adults with ADHD by linking Norwegian national registries and compared them with the remaining adult population (born 1967–1997, ADHD and bipolar during 2004–2015, other psychiatric disorders 2008–2015). Prevalence differences (PDs) and prevalence ratios (PRs) of psychiatric disorders were determined by Poisson regression. Interaction by gender was evaluated on additive (PDs) and multiplicative (PRs) scales. Proportions of psychiatric disorders attributable to ADHD were calculated.ResultsWe identified 40 103 adults with ADHD (44% women) and 1 661 103 adults (49% women) in the remaining population. PDs associated with ADHD were significantly larger in women than in men for anxiety, depression, bipolar and personality disorders, for example depression in women: 24.4 (95% CI, 23.8–24.9) vs. in men: 13.1 (12.8–13.4). PDs were significantly larger in men for schizophrenia and substance use disorder (SUD), for example SUD in men: 23.0 (22.5–23.5) vs. in women: 13.7 (13.3–14.0). Between 5.6 and 16.5% of psychiatric disorders in the population were attributable to ADHD.ConclusionThe association between ADHD and psychiatric comorbidities differed significantly among men and women. Clinicians treating adults with ADHD should be aware of these frequent and gender‐specific comorbidities, such that early treatment can be offered.

BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) share common genetic factors but seem to have specific patterns of psychiatric comorbidities. There are few systematic studies on adults; therefore, we compared psychiatric comorbidities in adults with these two neurodevelopmental disorders using population-based data and analyzed their genetic correlations to evaluate underlying factors. METHODS: Using data from Norwegian registries, we assessed patterns of psychiatric disorders in adults with ADHD (n = 38,636; 2.3%), ASD (n = 7528; 0.4%), and both diagnoses (n = 1467; 0.1%) compared with the remaining adult population (n = 1,653,575). We calculated their prevalence ratios (PRs) and differences using Poisson regression, also examining sex-specific relations. Genetic correlations (r g ) among ADHD, ASD, and the examined psychiatric disorders were calculated by linkage disequilibrium score regression, exploiting summary statistics from relevant genome-wide association studies. RESULTS: For all psychiatric comorbidities, PRs differed between ADHD and ASD. Associations were strongest in individuals with ADHD and ADHD1ASD for most comorbidities, in both men and women. The relative prevalence increase of substance use disorder was three times larger in ADHD than in ASD (PR ADHD , 6.2; 95% confidence interval [CI], 6.1-6.4; PR ASD , 1.9; 95% CI, 1.7-2.2; p , .001); however, the opposite was true for schizophrenia (PR ASD , 13.9; 95% CI, 12.7-15.2; PR ADHD , 4.4; 95% CI, 4.1-4.7; p , .001). Genetic correlations supported these patterns but were significantly different between ADHD and ASD only for the substance use disorder proxies and personality traits (p , .006 for all). CONCLUSIONS: Adults with ADHD, ASD, or both ADHD and ASD have specific patterns of psychiatric comorbidities. This may partly be explained by differences in underlying genetic factors.

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