While most bereaved individuals cope adaptively with the loss of a loved one, a significant minority experiences more severe and complicated grief reactions. Complicated grief reactions is an umbrella term for different types of post-loss complications, including symptoms of Prolonged Grief Disorder (PGD), depression, anxiety, and posttraumatic stress. These post-loss complications may all cause persistent suffering and functional impairment, thus pointing to a need for efficacious treatment.

While Cognitive Behavioural Therapy (CBT) is a relatively well-documented efficacious treatment for symptoms of PGD, depression, anxiety, and posttraumatic stress in the period after a loss, the relative efficacy of a transdiagnostic individually delivered versus group-based CBT for these types of complicated grief reactions (CBTgrief) remain unknown. Furthermore, little evidence exists about the relative cost-effectiveness of individually delivered versus group-based CBTgrief and why and how it works. The theory of CBTgrief proposes that it works by targeting three maintaining mechanisms in PGD: 1) Insufficient integration of the loss, 2) negative loss-related cognitions, and 3) depressive and anxious avoidance. These maintaining mechanisms have also shown to be statistically associated with depression, anxiety, and posttraumatic stress in the period after a loss, suggesting that different types of complicated grief reactions might share some of the same maintaining mechanisms. However, this proposed theory of change has yet to be empirically tested as a whole.

These knowledge gaps are crucial for the understanding of efficacious and cost-effective treatment formats as well as central treatment mechanisms in the psychological treatment of complicated grief reactions. The present study thus aims to examine the relative efficacy of an individually delivered versus group-based CBTgrief by means of a randomized non-inferiority trial. Secondary aims include an investigation of the relative cost-effectiveness of individually delivered versus group-based CBTgrief as well as treatment mediators. Finally, explorative analyses of potential moderators of intervention effects of CBTgrief will be conducted.

Aims of the study:

1. Evaluate the relative efficacy of an individually delivered versus group-based CBTgrief.
2. Evaluate the relative cost-effectiveness of an individually delivered versus group-based CBTgrief.
3. Examine the theoretically proposed treatment mediators of CBTgrief.
4. Explore loss-related and sociodemographic characteristics as possible moderators of intervention effects.

Primary hypothesis:

Group-based CBTgrief will show non-inferiority (i.e., equal efficacy) in reducing symptoms of PGD compared to individually delivered CBTgrief at six months follow-up.

Secondary hypotheses:

1. Group-based CBTgrief will show non-inferiority (i.e., equal efficacy) in reducing symptoms of posttraumatic stress, depression, and anxiety compared to individually delivered CBTgrief at six months follow-up.
2. Group-based CBTgrief will be more cost-effective than individually delivered CBTgrief.
3. The observed effect of CBTgrief is mediated by changes in theoretically proposed maintaining mechanisms of complicated grief reactions (i.e. insufficient integration of the loss; negative loss-related cognitions; depressive and anxious avoidance).
4. Gender, level of education, age, baseline grief symptom level, type of loss, circumstances of the loss, time since loss, and number of additional losses will moderate the observed effects of CBTgrief.
5. Additional exploratory analyses include an additional matched comparison group, who have not received treatment in order to compare the effect of individual and group-based CBTgrief to a non-treatment group. This group will be extracted from a large-scale survey study: The Aarhus Bereavement Study (NCT03049007). Here, it is hypothesized that CBTgrief will have a statistically significant medium size effect on symptoms of PGD at six months follow-up compared to a matched comparison group, who did not receive treatment.

Design: The present study is conducted as a randomized non-inferiority trial of individually delivered versus group-based CBTgrief using block randomization.

Participants: Participants are recruited from the Danish National Center for Grief (DNCG), which is a Danish national organization that provide specialized psychological therapy to bereaved individuals who have lost a loved one. The therapists at the DNCG will screen and treat bereaved elderly people for complicated grief reactions with CBTgrief at their clinics in Odense and Copenhagen, Denmark. DNCG identifies participants through consultants, local practitioners, self-referral, and the DNCG grief support line.

Assessment points: Participants will be assessed at pre-, mid-, and post-intervention as well as at three and six months follow-up (T1-T5). Additionally, data on healthcare utilization will be retrieved from the Danish national registers concerning use of health care services such as visits to general practitioners, psychologists etc.

Sample size: A group sample size of 2x64 will enable us to detect non-inferiority between individually delivered and group-based CBTgrief with a non-inferiority of -0.5 SD on the primary outcome, i.e. symptoms of PGD, and a statistical power of 0.80. The true difference is assumed to be 0.0 and the one-sided significance level (alpha) of the test is 0.025. Based on an estimated dropout rate of 20% the total number of participants needed to recruit is N=160 participants.

Inclusion Criteria:

1. Age ≥ 65 years (older adult).
2. Lost a loved one (e.g., spouse, partner) ≥ 6 months ago.
3. Clinically relevant symptoms of one or more types of complicated grief reactions (i.e. symptoms of prolonged grief (PG-13 ≥ 29), depression (CESD-10 ≥ 10), anxiety (GAD-7 ≥ 10), and/or posttraumatic stress (PCL ≥ 31)).

Exclusion Criteria:

1. No clinically relevant symptoms of one or more types of complicated grief reactions (i.e. symptoms of prolonged grief, depression, anxiety and/or posttraumatic stress).
2. No informed consent given.
3. Insufficient Danish proficiency.
4. Inability to transport oneself to the clinic.
5. Severe psychopathology (e.g., schizophrenia).
6. Severe cognitive impairment (e.g., Alzheimer's disease).
7. Substance abuse.
8. Acute suicidal ideation.

However, the investigator, therapists, and participants are masked in terms of not knowing which treatment the participants will be randomized to until after the completion of baseline assessment (T1).