The main aim of this project is to determine the short and long-term effectiveness of an out-patient treatment for patients with anorexia nervosa. Specifically, we will measure whether TBT-S in addition to treatment as usual (TAU) will be more effective than TAU alone in reducing eating disorder psychopathology. Assessments will be conducted at four timepoints; pre and post TBT-S, and at 3 and 12 months follow-up. Primary outcome measure is eating disorder psychopathology, with the hypothesis that patients receiving TBT-S in addition to TAU will show significantly greater reduction in eating disorder psychopathology from TBT-S treatment admission to 3 month follow-up, compared to controls.

Participants in the intervention arm will receive five days of TBT-S in addition to treatment as usual. TBT-S is administered to three to six adult anorexia nervosa patients with up to four supports per patient. The treatment structure consists of five consecutive days of treatment, up to 7,5 hours each day. Staff requirements for TBT-S are three clinicians, one dietician and one medical staff. Adults referred to a local psychiatric centre (DPS) for out-patient anorexia nervosa treatment, and their supports, will be eligible to participate in the study.

Inclusion Criteria:

• Age ≥18, all genders
• A Diagnostic and Statistical Manual of Mental Disorders (DSM-5) diagnosed anorexia nervosa disorder (F50.0, F50.01, F50.02, also including F50.9 - atypical anorexia nervosa)
• Willingness to have Support(s) participate in treatment
• Medically stable

Exclusion Criteria:

• Intellectual developmental disorder or intellectual disability; psychotic disorder or other psychopathology that may affect or prevent participation in the study
• diagnosed alcohol or other substance use disorder within 3 months prior to study initiation
• ongoing inpatient treatment at the time of study enrollment (participants currently in inpatient care must be discharged and engaged in outpatient treatment before participating in the TBT-S week

There are no plans to make individual participant data (IPD) available to other researchers.