Chen Q
BMJ. 2014 Jun 18;348:g3769. doi: 10.1136/bmj.g3769.

Abstract
OBJECTIVE:
To investigate the association between drug treatment for attention-deficit/hyperactivity disorder (ADHD) and risk of concomitant suicidal behaviour among patients with ADHD.

DESIGN:
Register based longitudinal study using within patient design.

SETTING:
Linkage of multiple national registers in Sweden.

PARTICIPANTS:
37 936 patients with ADHD born between 1960 and 1996 and followed from 2006 to 2009 for treatment status by ADHD drug treatment and suicide related events (suicide attempt and completed suicide).
MAIN OUTCOME MEASURE:
Incidence rate of suicide related events during ADHD drug treatment periods compared with that during non-treatment periods.

RESULTS:
Among 37 936 patients with ADHD, 7019 suicide related events occurred during 150 721 person years of follow-up. At the population level, drug treatment of ADHD 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 comparison showed a reverse association between ADHD drug treatment and rate of suicide related events (0.89, 0.79 to 1.00). Among stimulant users, a reduced within patient rate of suicide related events was seen during treatment periods (0.81, 0.70 to 0.94). Among non-stimulant/mixed users, no significantly increased within patient rate of suicide related events during non-stimulant treatment periods was seen (0.96, 0.72 to 1.30).

CONCLUSIONS:
This study found no evidence for a positive association between the use of drug treatments for ADHD and the risk of concomitant suicidal behaviour among patients with ADHD. If anything, the results pointed to a potential protective effect of drugs for ADHD on suicidal behaviour, particularly for stimulant drugs. The study highlights the importance of using within patient designs to control for confounding in future pharmacoepidemiological studies.