Complicated grief can affect a large number of individuals who have lost a relative due to cancer.

To assess the efficacy of a cognitive–behavioral grief therapy (CBGT) group for complicated grief (CG) in those who have lost a relative due to cancer in comparison with a psychoeducational and emotional expression intervention group (PSDEEI).

A randomized clinical trial was used, in which 249 relatives of deceased cancer patients with CG were randomly assigned to CBGT or PSDEEI. Complicated grief (Inventory of Complicated Grief [ICG]), depression (Beck Depression Inventory [BDI-II]), hopelessness (Beck Hopelessness Scale [BHS]), anxiety (Beck Anxiety Inventory [BAI]) symptoms, and general health (Goldberg’s General Health Questionnaire [GHQ28]) were assessed at pretreatment, posttreatment, and follow-up at 6 and 12 months.

The CBGT group improved significantly (p < 0.001), with the scores in ICG, BDI-II, BAI, BHS, and GHQ28 (p < 0.001) being higher than those for the PSDEEI group in each of the assessed moments, with high effect sizes: ICG (η2 = 0.16), BDI (η2 = 0.10), BAI (η2 = 0.06), BHS (η2 = 0.21), and GHQ28 (η2 = 0.21). At the 12-month follow-up, the number of cases of CG decreased by 81.1% for the CBGT group vs. 31.7% in the PSDEEI group.

The CBGT treatment was effective for CG, depression, anxiety, and hopelessness symptoms and for mental health and was superior to the PSDEEI treatment.