Generalized anxiety disorder (GAD) is a serious and long-lasting condition that can greatly reduce quality of life, work functioning, and use of health services. Metacognitive therapy (MCT) is an effective treatment for GAD, but it is not yet known whether individual MCT or group-based MCT provides the best results for patients.

This randomized controlled trial will compare two formats of MCT: individual treatment and group-based treatment (g-MCT). A total of 64 adults with GAD (32 in each treatment arm) will participate after providing informed consent. Participants will complete questionnaires, undergo clinical assessments, and allow the study to collect relevant health information from official registries.

The main aim of the study is to determine whether group-based MCT is non-inferior to individual MCT. A non-inferiority design tests whether the group format is not meaningfully less effective than the individual format. If group MCT is shown to have similar effects on anxiety symptoms and functioning, it could offer an efficient and resource-saving alternative in routine clinical care.

This will be the first study to systematically compare these two treatment formats in a real-world clinical setting. If group MCT proves to be as effective as individual therapy, it may help increase access to evidence-based treatment for people with GAD, reduce strain on mental health services, and support the development of more accessible and cost-effective care.

Generalized anxiety disorder (GAD) is a chronic and disabling condition characterized by persistent and uncontrollable worry. Individuals with GAD frequently experience reduced quality of life, impaired daily functioning, and elevated use of health care services. Although effective psychological treatments exist, including metacognitive therapy (MCT), it remains unclear which treatment delivery format provides the best balance of clinical effectiveness and efficient use of resources.

MCT is an evidence-based treatment targeting the metacognitive processes that maintain excessive worry, including beliefs about the usefulness and uncontrollability of worrying and the cognitive-attentional syndrome (CAS), a pattern of worry, rumination, threat monitoring, and unhelpful coping behaviors. Individual MCT has demonstrated strong and consistent effects across several clinical trials, while group-based MCT (g-MCT) has shown promising preliminary results. However, the two formats have never been directly compared in a randomized trial conducted in routine clinical care. This represents a meaningful gap in the research literature and limits the ability of services to make informed decisions about how to organize treatment.

This study addresses this gap by conducting a randomized controlled trial (RCT) comparing individual MCT with group-based MCT for adults with GAD. An RCT design is chosen because it provides the highest level of evidence for causal inference about treatment effects. A non-inferiority framework is used to test whether group MCT is not meaningfully less effective than individual MCT. This design is appropriate when an alternative treatment may offer practical advantages-such as lower cost, greater accessibility, or more efficient resource use-while aiming to demonstrate that clinical outcomes remain comparable.

A total of 64 adults with a primary diagnosis of GAD will be enrolled and randomized to either individual MCT or group MCT. Both interventions follow established MCT protocols and are delivered by trained clinicians. Treatment focuses on reducing worry, modifying maladaptive metacognitive beliefs, and promoting flexible attentional control. Data collection includes validated self-report questionnaires, structured clinical assessments, and-with participant consent-information obtained from official national registers to assess work participation and sick leave pre and post treatment.

Evaluating group-based MCT is particularly important in the context of mental health services, where demand often exceeds available treatment resources. If group MCT is found to be non-inferior to individual MCT, it could make it possible to offer effective therapy to more patients within the same amount of therapist time. This has the potential to reduce waiting times, improve access to evidence-based treatment, and support more sustainable use of clinical resources.

The findings from this trial will contribute to the evidence base for MCT, clarify which treatment format is most appropriate for adults with GAD, and inform clinical guidelines and service organization. As the first randomized study to directly compare individual and group MCT in a real-world clinical setting, the results may have meaningful implications for both clinical practice and mental health policy.

Inclusion Criteria:

Adults with a primary diagnosis of generalized anxiety disorder (GAD). GAD-7 score ≥ 10 at screening/baseline. Participants must endorse that they experience problems with excessive worry

Exclusion Criteria:

1. Bipolar disorder;
2. Psychosis;
3. Ongoing substance abuse/dependence;
4. Intellectual disability based on previous medical history;
5. Eating disorder in need of medical attention;
6. Unwillingness to refrain from anxiolytic drugs during the treatment;
7. Current suicidal ideation with plan and intent;
8. Taking an unstable dose of antidepressant, with recent dose-change within the last 4 weeks;
9. Known cluster A or B personality disorder;
10. Serious medical comorbidity (e.g.: cancer, severe renal failure)
11. Language difficulties in need of an interpreter.

Our ethical approval from the Regional Committees for Medical and Health Research Ethics (REK) does not allow us to share individual participant data (IPD). In accordance with the conditions set by REK, all data are stored securely and cannot be made available to external researchers. Data sharing is further restricted by Norwegian privacy legislation (GDPR) and institutional data protection requirements.

The raters conducting the CSR rating are trained independent clinicans, and are masked regarding treatment arms.