Experimental fMRI Study of Guanfacine and Lisdexamfetamine in ADHD Adolescents

Inclusion Criteria: * Age range: 8-20 years * Medication-naïve or non-medicated for two weeks or on stimulant medication, and willing to take the medication off for 48 hours before scans. * Meeting DSM-5 diagnosis of ADHD * Score above clinical cut-off on the ADHD module of the Kiddie Schedule for Affective Disorders and Schizophrenia (K-SADS) (Kaufman et al., 1997) * Score above clinical cut-off for ADHD on the short forms of the Conners Parent Rating Scales, CPRS (Conners et al., 2008) * Score above cut-off on the ADHD Rating Scale, ADHD-RS (DuPaul, et al., 1998) * IQ \> 70 as tested on the WASI-II (Wechsler et al., 1999) * Mood and depression symptoms will be allowed as long as they are not the primary diagnosis. Exclusion Criteria: * IQ \< 70 (Wechsler et al., 1999). * Comorbidity with schizophrenia, bipolar disorder, learning disability, OCD, severe depression with current suicidal behaviour (as assessed by a clinical interview) * Neurological problems, i.e. a history of severe neurological illness, e.g. brain tumour, epilepsy or a history of symptomatic seizures, polyneuropathy etc. * Substance abuse history * Other illness (cardiovascular, renal, hepatic, metabolic) that would impact the data integrity or safety of the subject (i.e. contraindicated to any of the treatments) as determined by the investigators * Contraindication to MRI. i.e., previous implantation of metallic material, pacemaker, implanted medication pumps, neural stimulators, claustrophobia * Unable …