OBJECTIVES: To estimate the prevalence of attention deficit hyperactivity disorder (ADHD) pharmacological treatment, and its demographic and clinical details, and to estimate the proportion of patients in the target group who stopped ADHD treatment and investigate possible factors for continuation or cessation of treatment. DESIGN: A pharmacoepidemiological study using an automated database and a qualititative study using patient interviews. Part 1 was a pharmacoepidemiological study that provided accurate data on use and cessation of ADHD drugs. Part 2 was an in-depth interview study to investigate the reasons, processes and outcomes of treatment cessation. SETTING: Part 1: primary care using the General Practice Research Database (GPRD). Part 2: secondary and tertiary care paediatric clinics, child and adolescent mental health and adult mental health clinics in London, Nottingham, Dundee and Liverpool. PARTICIPANTS: Part 1: patients were 15-21 years old during the study period (1 January 2001 and 31 December 2004), had at least one prescription for methylphenidate, dexamfetamine or atomoxetine and had at least 1 year of research-standard data available in the GPRD. Part 2: patients fulfilled Part 1 criteria, had a diagnosis of ADHD as detected by a predefined algorithm and had been treated with methylphenidate, dexamfetamine or atomoxetine for at least 1 year. Child and adolescent psychiatrists, adult psychiatrists and paediatricians involved in the treatment of young people with ADHD were also interviewed as part of the study. RESULTS: Part 1: prevalence of prescribing averaged across all ages increased eightfold, from 0.26 per 1000 patients in 1999 to 2.07 per 1000 patients in 2006. The increase in prevalence in the younger patients was less evident in the older patients. Prevalence in 15-year-old males receiving a study drug prescription increased from 1.32 per 1000 patients in 1999 to 8.31 per 1000 patients in 2006, whereas the prevalence in 21-year-olds rose from 0 per 1000 patients in 1999 to 0.43 per 1000 patients in 2006. Survival analysis showed that the rate of treatment cessation largely exceeded the estimated rate of persistence of ADHD. The reduction in prescribing was most noticeable between 16 and 17 years of age. Kaplan-Meier analysis showed that approximately 18% of patients restarted treatment if they had stopped treatment after the age of 15. Patients who restarted treatment were more likely to restart within the first year following treatment cessation. Part 2: the Child Health and Illness Profile (CHIP) was chosen as the quality of life questionnaire for the Part 2 study because the CHIP-CE scale has been validated in children with ADHD in the UK. Because of the age range of participants, the adolescent version (CHIP-AE) was administered to patients after interview. Of the 15, a total of nine patients finished the questionnaire. Interviews showed that although some young people felt able to cope after stopping medication, others felt the need to restart to control symptoms. Some patients had difficulty re-engaging with services and clinicians recognised the lack of services for young adults. Patients continuing on treatment considered cessation as an option for the future, but were concerned about the process of stopping and its impact on behaviour. CONCLUSIONS: Part 1 study demonstrated that the prevalence of prescribing by GPs to patients with ADHD dropped significantly from age 15 to 21. The fall in prescribing was greater than the reported age-related decrease in symptoms, raising the possibility that treatment is prematurely discontinued in some young adults where ADHD symptoms persist. Part 2 of the study identified that some young adults had difficulty in obtaining treatment after discharge from paediatric services. Future work should include randomised placebo-controlled trials into long-term treatment with stimulants, particularly methylphenidate.