The main exposure was ADHD medication identified in the Prescribed Drug Register using the Anatomical Therapeutic Chemical (ATC) classification system. Before 2008, ADHD medication could be prescribed only by child and adolescent psychiatrists, neuro-pediatricians or physicians licensed following individual application and Medical Products Agency approval. Since then, all specialists in psychiatry are licensed to prescribe. Nevertheless, ADHD medication to both children and adults has increased exponentially since 200514 . Methylphenidate (N06BA04) is recommended for first-line drug treatment, whereas amphetamine (N06BA01) and dexamphetamine (N06BA02) are more rarely prescribed. The non-stimulant atomoxetine (N06BA09) is also regularly used14 .
In accordance with previous studies14 ,15 (link), an individual was defined as receiving treatment during the time interval between two prescriptions of ADHD medication, unless prescriptions occurred more than 6 months apart. Thus, a treatment period was defined as a sequence of prescriptions, with no more than 6 months between two consecutive prescriptions. The start of treatment was defined as the date of the first prescription and end of treatment as the date of the last prescription. During intervals of 6 months or more without any prescriptions, an individual was considered to be off treatment. Patients receiving only one prescription (N=914) were considered to be off treatment. To determine whether individuals were receiving treatment at start and end of follow-up, the follow-up period was set to 1/1/2006 to 12/31/2009 as the Prescribed Drug Register only covered the period 7/1/2005 to 6/30/2010.
The main outcome was any conviction for a crime. If no date of crime was recorded, the date of the conviction was used. In sensitivity analyses, we also investigated less severe (i.e., not associated with custodial sentences), violent, and substance-related crimes25 (link) (for crime categories and prevalence seeTable 1 ).
Individuals diagnosed with conduct, oppositional defiant, antisocial personality, or substance abuse disorders were identified through the Patient Register (ICD-9: 313.81, 312, 301.7, 291, 292, 303, 304, 305; ICD-10: F91, F60.2 and F10-F19).
In accordance with previous studies14 ,15 (link), an individual was defined as receiving treatment during the time interval between two prescriptions of ADHD medication, unless prescriptions occurred more than 6 months apart. Thus, a treatment period was defined as a sequence of prescriptions, with no more than 6 months between two consecutive prescriptions. The start of treatment was defined as the date of the first prescription and end of treatment as the date of the last prescription. During intervals of 6 months or more without any prescriptions, an individual was considered to be off treatment. Patients receiving only one prescription (N=914) were considered to be off treatment. To determine whether individuals were receiving treatment at start and end of follow-up, the follow-up period was set to 1/1/2006 to 12/31/2009 as the Prescribed Drug Register only covered the period 7/1/2005 to 6/30/2010.
The main outcome was any conviction for a crime. If no date of crime was recorded, the date of the conviction was used. In sensitivity analyses, we also investigated less severe (i.e., not associated with custodial sentences), violent, and substance-related crimes25 (link) (for crime categories and prevalence see
Individuals diagnosed with conduct, oppositional defiant, antisocial personality, or substance abuse disorders were identified through the Patient Register (ICD-9: 313.81, 312, 301.7, 291, 292, 303, 304, 305; ICD-10: F91, F60.2 and F10-F19).
