Transdiagnostic Internet-delivered cognitive behaviour therapy with therapist support offered once-weekly or once-weekly supplemented with therapist support within one-business-day: Pragmatic randomized controlled trial

In routine care, internet-delivered cognitive behaviour therapy (iCBT) regularly includes therapist support delivered via secure email, but the optimal response time to emails is unknown. In this study, we compared the benefits of therapists providing support once-weekly versus therapists providing support once-weekly supplemented with a one-business-day response to all patient emails. This pragmatic randomized controlled trial included therapists employed by a specialized iCBT clinic or community mental health clinics, where providing iCBT is a secondary service. Patients with depression and/or anxiety who enrolled in transdiagnostic iCBT (5 core lessons over 8 weeks) were randomized to: 1) once-weekly support supplemented with a one-business-day response to patient emails by specialized therapists (n = 233); 2) once-weekly support also offered by specialized therapists (n = 216); or 3) once-weekly support offered by community clinic therapists (n = 226). Outcomes were measured at 8, 12, 24, and 52-weeks post-enrollment. Patient engagement and treatment experiences (e.g., treatment satisfaction, therapist alliance) were also assessed and a focus group was conducted with therapists. Supplementing once-weekly therapist support with a one-business-day response to patient emails resulted in therapists sending more emails to patients (M: 13 versus 9) and required more therapist time over treatment (M: 155 versus 109 min), but was not associated with improved outcomes, patient engagement or treatment experiences. All groups showed large improvements in symptoms of depression and anxiety maintained at 52-week follow-up, strong engagement and positive treatment experiences. Therapists viewed challenges of responding to patient emails within one-business-day to outweigh benefits. Contrary to expectations, supplementing once-weekly therapist support with a one-business-day response to all patient emails did not benefit patients and increased therapist time as well as therapist challenges when delivering iCBT in routine care.