Investigate the clinical subtypes and the biological markers to personalize the use n-3 PUFAs (EPA, DHA, and EPA/DHA) in MDD.

In this proposal, the investigators aim to explore the clinical subtypes and biological markers to personalize the use n-3 PUFAs (EPA, DHA, and EPA/DHA) in MDD. By stratifying the subjects with (versus without) remission and treatment response, the biological markers are expected to have important prediction effects in future clinical practice.

Inclusion Criteria:

• the diagnostic criteria of DSM-IV for MDD
• 18 to 65 years old
• pre-study ratings of 18 or greater on the 21-item Hamilton Rating Scale for Depression (HAMD)
• physically healthy under comprehensive evaluations in medical history, physical examination, and laboratory parameters tests
• have not received any psychiatric treatment in 2 weeks
• competent to receive a full explanation of this study and give written informed consent.

Exclusion Criteria:

• a recent or past history of other DSM-IV AxisI diagnoses besides unipolar major depression, including psychotic disorders, organic mental disorders, impulse control disorders, substance use disorder or substance abuse (last 6 months prior to the study), and bipolar disorders
• AxisII diagnoses, including borderline and antisocial personality disorder
• a notable medical comorbidity
• acutely suicidal ideation and attempt were noted that close monitoring such as hospitalization is necessary
• regular consumption of omega-3 PUFAs supplements or a habit of eating fish equal or more than 4 times per week