Attachment-Based Therapy as adult, one-on-one work shares a theory with a better-studied family model, Attachment-Based Family Therapy, used mainly with suicidal and depressed adolescents. The evidence is strongest there, and even that base is still small. Adult individual attachment work is clinically common and thinner in trials. That is worth saying plainly. What follows is related research, not a claim that adult ABT has the same outcome data as a branded family protocol. If you are an adult coming for relationship patterns, treat the adolescent family trials as context for the theory, not as a forecast of your own result.
Schulte-Frankenfeld, P. M., et al. (2024), Clinical Psychology in Europe. A systematic review and meta-analysis of Attachment-Based Family Therapy for suicidal adolescents found it was not significantly more effective than comparison treatments across the small set of trials, and the authors advised caution about using it as a stand-alone intervention.
Diamond, G., Russon, J., & Levy, S. (2016), Family Process. A review of the ABFT clinical model summarized several trials and process studies suggesting the family approach can help with adolescent depression, suicidality, and trauma by repairing attachment ruptures, while remaining a related model rather than adult individual attachment therapy.
Diamond, G. S., et al. (2010), Journal of the American Academy of Child and Adolescent Psychiatry. In a randomized trial, suicidal adolescents who received ABFT had greater reductions in suicidal ideation than those in enhanced usual care, with higher rates of clinical recovery after three months. This is a family treatment for teens. It is not a trial of adult one-on-one attachment-based therapy.
Montero-Marín, J., et al. (2018), Frontiers in Psychiatry. In a randomized trial of 42 people with fibromyalgia, attachment-based compassion therapy was associated with better day-to-day functioning than relaxation training, with the difference still present at three months. This studied a specific attachment-based compassion protocol in one patient group. It is not a trial of adult attachment-based therapy in general.