Fitzgerald C, et al. - Researchers examined whether a comorbid psychiatric disorder increases the suicidal behavior intensity among persons with attention-deficit hyperactivity disorder (ADHD) (ie suicide attempts and deaths by suicide). They followed a cohort of 2.9 million individuals from January 1, 1995, until December 31, 2014, using nationwide registers covering the entire population of Denmark, covering more than 46 million person-years. Among persons with ADHD, they observed 697 suicidal outcomes during follow up of 164,113 person-years. This group vs those without ADHD showed an IRR of suicidal behavior of 4.7. Persons with ADHD only vs those without any psychiatric diagnoses had a 4.1-fold higher rate. The IRR was higher yet for persons with ADHD and comorbid disorders (IRR: 10.4). Findings thereby support the link between ADHD and an elevated rate of suicidal behavior, which significantly elevates in the presence of comorbid psychiatric disorders.