The study, published in JAMA (the prestigious journal of the American Medical Association), was a large cohort study of 148,578 people diagnosed with ADHD in Sweden. It included both adults and children.

In a cohort study, a group of people who share a common characteristic (in this case a diagnosis of ADHD) are followed over time to see how many develop a particular health outcome of interest (in this case the outcome was death).

Could ADHD Drugs Reduce The Risk Of Early Death? - Study Finds