TRAIT is an open-label observational study to evaluate treatment response to selective-serotonin reuptake inhibitors (SSRIs) and selective-norepinephrine reuptake inhibitors (SNRIs) among individuals meeting criteria for Major Depressive Disorder (MDD) and seeking enrollment in investigational trials.

Inclusion Criteria:

• Participant has signed an ICF prior to any study-specific procedures being performed.
• Participant is male or female of age ≥ 18 years old.
• Participant has a diagnosis of MDD as confirmed by the MINI semi-structured diagnostic interview and ≥ 14 HAM-D total score.
• Participant is in good physical health and, in the opinion of the investigator, is a suitable candidate for treatment with an ADT.

Exclusion Criteria:

• Participant is pregnant, breast-feeding, or planning to become pregnant.
• A history or presence of a clinically significant hepatic, renal, gastrointestinal, cardiovascular, endocrine, respiratory, immunologic, hematologic, dermatologic, or neurologic abnormality, which in the opinion of the investigator may impact participant safety or study results.
• Participant has a history of any psychiatric condition other than MDD, which in the opinion of the investigator is primary, or any other psychiatric or neurologic disorder or symptom that could pose undue risk to the participant or compromise the study.
• Any participant who represents an acute suicidal risk in the opinion of the investigator.
• Moderate or severe substance use disorder within 90 days prior to screen, according to DSM-5 criteria that in the opinion of the investigator could pose undue risk to the participant, or compromise the study.
• Any condition that, in the opinion of the investigator, makes the participant unsuitable for the study.

Adults who currently meet the Diagnostic and Statistical Manual - Version 5 (DSM-5) criteria for Major Depressive Disorder and are seeking enrollment in an industry-sponsored clinical trial of a second- or third-line antidepressant.