A Single-blind Randomised Controlled Trial of Group Cognitive Behavioural Therapy (CBT) Versus Activity Group Control Condition for Adults With Attention Deficit Hyperactivity Disorder (ADHD)

Despite medical treatment, many adults with ADHD experience residual symptoms that negatively affect work performance and social life. Hence, several psychological interventions targeting these symptoms have been developed, but the treatment effects are still unclear due to lack of controlled clinical trials.

In this single-blind randomised controlled clinical trial, the reseachers will evaluate the effects of group CBT based on Safren's manual "CBT for ADHD/Mastering Your Adult ADHD" compared to an active control group. The control intervention is a manualised activity group that contains the same non-specific therapeutic elements as the treatment but no active CBT components. For dose equivalence, activity groups will be given with the same same number and length of sessions, and the same frequency, as the treatment conditions. Since therapist experience is known to influence outcomes, the activity groups will be held by staff with equivalent training and experience to those giving the treatment groups.

Consenting patients assessed eligible for treatment will be randomly assigned to treatment or control group using a standard digital randomisation generator with an allocation of 1:1. Patients and clinicians rating outcomes will be blind to group assignment.

Pre- and post intervention, and at 6 months and 12 months follow-up, the patient's ADHD symptoms, symptoms of anxiety and depression and general functioning will be assessed by experienced clinicians and with validated self-rating scales. Treatment fidelity and expectation will be compared for the therapy and control groups and adverse events will be registered.

An exact power calculation for estimation of sample sizes cannot be performed since effect sizes are not known. Based on a previously published studies of Safren's CBT individually administered, and general consensus of what is a clinically meaningful improvement in psychological treatments for other psychiatric diagnoses, we expect that 60 patients per arm will be sufficient for detection of clinically relevant effect sizes of approximately Cohen's d 0.3-0.4. A statistician will make a blind Bayesian stop analysis for every 20-25 patients, and based on the results we can decide to halt the study if sufficient power has been achieved earlier than after 60 patients. Full attrition analysis with intention to treat (ITT) analysis will be performed to investigate and minimize attrition bias.