Medication for Attention-Deficit/Hyperactivity Disorder and Suicidal Behavior: A Register Based Study
METHODS: We used data obtained from Swedish national registers to identify a cohort of individuals born between 1960 and 1996 with a clinical diagnosis of ADHD (N=37,936 patients). Patients were followed for 4 years (2006-2009) for their medication treatment status and suicide-related events consisting of suicide attempt and completed suicide. Cox and stratified Cox regression models were used to compare the incidence rates of suicide-related events during treatment periods and non-treatment periods at the population level (between patients) and within patients.
RESULTS: Among 37 936 patients with ADHD, 7019 suicide-related events occurred during 150 721 person years of follow-up. At the population level, the use of ADHD medication was associated with an increased rate of suicide-related events (hazard ratio 1.31, 95% confidence interval 1.19 to 1.44). However, the within-patient comparisons showed a reversed association between the use of ADHD medication and rate of suicide-related events (0.89, 0.79 to 1.00). Among stimulant users, we observed a reduced within-patient rate of suicide-related events during treatment periods (0.81, 0.70-0.94). Among non-stimulant/mixed users, we observed no significantly increased within-patient rate of suicide-related events during non-stimulant treatment periods (0.97, 0.72 to 1.31).
CONCLUSIONS: We found no evidence for a positive association between the use of ADHD medication and the risk of concomitant suicidal behavior among patients with ADHD. A slightly protective effect of stimulants on concomitant suicidal behavior was observed. The study highlights the importance of using quasi-experimental approaches to address selection effects in future pharmaco-epidemiological studies.