ALTO-300 in Depression (ALTO-300-004)

Inclusion Criteria:

• Have a diagnosis of moderate to severe major depressive disorder
• Currently taking a SSRI, SNRI, or bupropion for at least 6 weeks with no dosemodifications in the past 2 weeks
• Must have failed to adequately respond to the current antidepressant medication
• Willing to comply with all study assessments and procedures
• Must not be pregnant or breastfeeding at time of enrollment or throughout study

Exclusion Criteria:

• Evidence of liver impairment or disease
• Active suicidal ideation
• Moderate to severe Alcohol Use Disorder
• Diagnosed bipolar disorder or psychotic disorder
• Has a history of hypersensitivity or allergic reaction to ALTO-300 or any of itscomponents/excipients
• Concurrent or recent participation in another clinical trial for mental illnessinvolving an investigational product or device