The study will assess the safety, tolerability, and pharmacokinetics of basimglurant compared to placebo after multiple ascending oral doses for up to 22 days in healthy subjects and in patients with MDD on stable selective serotonin reuptake inhibitor (SSRI) or serotonin-norepinephrine reuptake inhibitor (SNRI) background therapy.

Inclusion Criteria:

• 18 to 65 years of age, inclusive
• Body weight at least 50 kg
• Healthy male or female subjects (Healthy Cohorts)
• Body mass index (BMI) 18 to 30 kg/m^2, inclusive (Healthy Cohorts)
• Nonsmoker for at least 90 days prior to dosing (Healthy Cohorts)
• Primary diagnosis of MDD without psychotic features (MDD Cohort)
• BMI 18 to 35 kg/m^2, inclusive (MDD Cohort)
• Current partial response to ongoing SSRI or SNRI antidepressant treatment at an adequate dose and for at least 4 weeks (MDD Cohort)
• Clinical Global Impression of Severity (CGI-S) score 3 or greater (MDD Cohort)
• Other regimens stable for at least 8 weeks prior to screening (MDD Cohort)

Exclusion Criteria:

• Pregnant or lactating women
• History of alcohol or substance abuse in the past 6 months
• Hepatitis B, hepatitis C, or human immunodeficiency virus (HIV)
• Clinically relevant electrocardiogram (ECG) abnormalities or a personal or family history of congenital long QT syndrome
• Participation in an investigational study within 90 days of screening
• Blood donation over 500 mL within 3 months of screening
• Hypersensitivity to any study medication or excipients
• Psychotic symptoms or comorbid mood disorder
• Significant suicide risk
• Major illness within 1 month before screening, or febrile illness within 1 week (Healthy Cohorts)
• Average alcohol consumption of more than 2 units per day (Healthy Cohorts)
• Multi-drug therapy for depression including antidepressants or adjunctive medications (MDD Cohort)
• Prior use of basimglurant (MDD Cohort)
• Cigarette use of greater than 1 pack per day (MDD Cohort)