Major depressive disorder (MDD) is one of the leading causes of disability worldwide, indicated as one of the two most disabling mental disorders by the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 (Vos et al., 2020). Despite several effective pharmacological and psychosocial interventions available globally, only about one-third of depressed patients achieve remission (Xiao et al., 2021). There is a need to establish scalable clinical management practices which utilize biopsychosocial assessments, formulate a differential diagnosis, and provide evidence-based treatments for patients with MDD (Hong et al., 2021). While significant evidence for effectiveness of Measurement Based Care (MBC) is found in clinical settings from high and middle-income countries, assessments of MBC compared with usual care for the treatment of MDD are yet to be completed in low-resource settings like LMICs. The aim of this trial is to determine the efficacy and safety of MBC in patients with MDD in comparison with standard care in Pakistan. In order to reduce the variance found in treatment-as-usual and isolate the impact of MBC, standard care for this trial will limit medication choices to either paroxetine or mirtazapine.

Hypothesis: The rates of response and remission, and time to response and remission would be significantly shorter in the MBC group, without greater dropout rates and side effect burden, compared with the standard treatment group.

Study design and setting This will be a multi-centre, with assessors blind to protocol and treatment group, parallel arm, randomized controlled trial (RCT). The study is a direct replication of a study conducted by Gou et al. (2015) in China.

Participants Participants will be recruited from psychiatric units of teaching and non-teaching hospitals in 6 centres: Karachi (population 23 million), Lahore (population 10 million), Rawalpindi (population 3 million), Hyderabad (population 2 million) and Quetta (population 1 million) and Multan (1.8 million).

Sample size The sample size of 120 participants for this exploratory trial is based on the study conducted by Guo et al.

Inclusion Criteria:

1. Adult outpatients age 18-65 of age
2. Diagnosis of nonpsychotic MDD established by treating psychiatrists and confirmed by a checklist based on DSM-5 criteria at study entry
3. Currently depressed with a score >17 on the 17-item Hamilton Depression Rating (HDRS-17)
4. Able to communicate effectively and give written informed consent
5. Resident of the trial catchment area.

Exclusion Criteria:

1. Lifetime history of drug or alcohol dependence; 2. Diagnosis of bipolar, psychotic, obsessive-compulsive, or eating disorders confirmed with DSM-5 criteria 3. History of a lack of response or intolerance to either of the two protocol antidepressants (paroxetine and mirtazapine) 4. Currently pregnancy or breastfeeding; 5. Suicide attempts in the current depressive episode; 6. Any major medical condition contraindicating the use of the protocol antidepressants.

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Only anonymized data will be shared with researchers

This will be an assessor blind, randomized controlled trial. Due to the nature of the interventions, it will be impossible to blind clinicians in participating centres or the participants themselves. Before assessments, participants will be asked not to reveal any information about treatment to assessors. To avoid unblinding, outcome assessors will be located separately from treatment providers, and we will assign new outcome assessors in cases of unintentional unblinding.