Inclusion Criteria:
1. Male or female subjects aged between 18 and 65 years, inclusive.
2. Subjects with a clinical diagnosis of Major Depressive Disorder (MDD) as determined by the investigator or qualified psychiatrist, based on standard clinical judgment.
3. Subjects with moderate to severe depression, defined as a Hamilton Depression Rating Scale (HAM-D-17) score ≥18 at both screening and baseline visits.
4. Subjects who are either:
* Planned to initiate treatment with escitalopram, or
* Have already started escitalopram therapy within ≤2 weeks prior to screening, provided that any prior antidepressant therapy was discontinued with an adequate washout period (≥2 weeks or ≥5 half-lives of the previous medication, whichever is longer) before baseline assessment.
5. Subjects who are medically stable, as assessed by the investigator based on medical history, physical examination, and any relevant laboratory investigations.
6. Subjects who are able and willing to provide written informed consent prior to participation in the study.
7. Subjects who are willing and able to comply with study procedures, treatment regimen, and scheduled study visits.
Exclusion Criteria:
1. High suicide risk, defined as:
* Presence of active suicidal ideation with intent or plan, or
* Subject considered by the investigator to be at significant risk of suicide.
* History of suicide attempt or self-harm
2. Presence of major psychiatric disorders other than MDD, including but not limited to:
* Bipolar disorder
* Schizophrenia or other psychotic disorders
3. Presence of severe or unstable medical conditions that may interfere with study participation or pose a risk to the subject, including but not limited to:
* Uncontrolled hepatic (liver) disease
* Significant renal (kidney) impairment
* Clinically significant cardiovascular disease
4. Known hypersensitivity or allergy to:
* Escitalopram
* Fish oil or omega-3 fatty acid or folic acid, or L-5-methyltetrahydrofolate supplements
5. Pregnant or lactating women, or women planning to become pregnant during the study period.
6. Use of concomitant medications or treatments that may confound study outcomes, including:
* Other antidepressants (unless in the process of being switched to escitalopram)
* use of omega-3 or fish oil or folic acid, or L-5-methyltetrahydrofolate supplements
7. Any condition or circumstance which, in the opinion of the investigator, may compromise subject safety, adherence to study procedures, or the integrity of study data.
8. History of substance abuse within 6 months prior to screening.
9. Prior treatment with electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), vagus nerve stimulation (VNS), or deep brain stimulation (DBS) during the current depressive episode.
10. Initiation of new psychotherapy or change in psychotherapy intensity within 8 weeks prior to screening.
11. Participation in other interventional or non-interventional studies within 3 months prior to screening.
12. High dietary intake of fish (≥3 times per week) or use of fish oil/n-3 PUFA/folate supplements within the past 6 months.
13. Moderate to severe anxiety disorders, as assessed by GAD-7.
14. Participation in another clinical study within 30 days.
