Experiencing traumatic life events is associated with an increased risk of common mental disorders (CMDs), but studies investigating this association within Indigenous populations are limited.

The aim of this study was to investigate associations between trauma and CMDs after controlling for other exposures.

Trauma exposures and CMD diagnoses were determined in a broadly representative sample of 544 Indigenous Australians, using a diagnostic clinical interview. Associations were determined by multivariate logistic regression.

Trauma exposure independently predicted CMDs. After adjustment for potential confounders, trauma exposure was associated with a 4.01-fold increased risk of a diagnosis of a CMD in the past 12 months. The increased risks were 4.38-, 2.65- and 2.78-fold of having an anxiety disorder, mood disorder or a substance use disorder, respectively. Trauma exposure and comorbid post-traumatic stress disorder was associated with a 4.53-fold increased risk of a diagnosis of a mood disorder, 2.47-fold increased risk of a diagnosis of a substance use disorder, and 3.58-fold increased risk of any diagnosis of a CMD, in the past 12 months. Experiencing both sexual and physical violence was associated with a 4.98-fold increased risk of a diagnosis of an anxiety disorder in the past 12 months.

Indigenous Australians experience significantly increased exposure to potentially harmful trauma compared with non-Indigenous Australians. Preventing and healing trauma exposure is paramount to reduce the high burden of CMDs in this population.

A four- to seven-fold increase in the prevalence of current mood, anxiety, substance use and any mental disorders in Indigenous adults compared with non-Indigenous Australians has been reported. A lifetime prevalence of major depressive disorder was 23.9%. High rates of comorbid mental disorders indicated a transdiagnostic approach to treatment might be most appropriate. The effectiveness of psychological treatment for Indigenous Australians and adjunct Indigenous spiritual and cultural healing has not previously been evaluated in controlled clinical trials.

This project aims to develop, deliver and evaluate the effectiveness of an Indigenous model of mental healthcare (IMMHC). Trial registration: ANZCTR Registration Number: ACTRN12618001746224 and World Health Organization Universal Trial Number: U1111-1222-5849.

The IMMHC will be based on transdiagnostic cognitive–behaviour therapy co-designed with the Indigenous community to ensure it is socially and culturally appropriate for Indigenous Australians. The IMMHC will be evaluated in a randomised controlled trial with 110 Indigenous adults diagnosed with a current diagnosis of depression. The primary outcome will be the severity of depression symptoms as determined by changes in Beck Depression Inventory-II score at 6 months post-intervention. Secondary outcomes include anxiety, substance use disorder and quality of life. Outcomes will be assessed at baseline, 6 months post-intervention and 12 months post-intervention.

The study design adheres to the Consolidated Standards of Reporting Trials (CONSORT) statement recommendations and CONSORT extensions for pilot trials. We followed the Standard Protocol Items for Randomised Trials statement recommendations in writing the trial protocol.

This study will likely benefit participants, as well as collaborating Aboriginal Medical Services and health organisations. The transdiagnostic IMMHC has the potential to have a substantial impact on health services delivery in the Indigenous health sector.