Investigator retired.

This is a two-arm double-blind prospective randomized controlled trial (RCT) to evaluate clinical impact of pharmacogenomic testing on the treatment of major depressive disorder. Participants will be randomly assigned to two groups: pharmacogenomic-guided therapy group (guided group) and treatment as usual group (TAU group). The primary hypothesis is the pharmacogenomic-guided treatment group will demonstrate significantly higher percent improvement in depression score compared to treatment-as-usual group.

To a large extent, variability in antidepressant efficacy can be explained by genetic variations that affect medication-metabolizing enzymes, drug transporters, and medication targets. Recent reviews demonstrated significant potential of pharmacogenomic testing in improving treatment of major depressive disorder. One of the major barriers towards successful implementation of pharmacogenomic testing for patients with major depressive disorder is lack of systematic evaluation of impact of this approach in routine clinical care settings. The major goal of this study is to systematically evaluate impact of comprehensive pharmacogenomic testing on the treatment of major depressive disorder in ambulatory setting.

Inclusion Criteria:

1. Clinical diagnosis of major depressive disorder (MDD)
2. Prescription of index antidepressant medications
3. Minimum score of 14 on the 17-item Hamilton Rating Scale for Depression (HAMD-17)

Exclusion Criteria:

1. Diagnosis of bipolar disorder (any type), schizophrenia, or schizoaffective disorders
2. Active diagnosis of substance abuse or dependence
3. Current suicidal ideation
4. Previous suicidal attempts
5. A person has already had pharmacogenetic testing done.