This is a multicenter, Phase 2, double-blind, randomized, parallel-arm, placebo-controlled clinical trial to evaluate the efficacy, safety, and tolerability of XEN1101 in subjects with Major Depressive Disorder.

The study is divided into 3 stages: Screening - up to 4 weeks duration; Treatment - 6 weeks duration; Follow-up - 4 weeks duration. The total study duration per subject is estimated to be approximately 14 weeks.

Key Inclusion Criteria:

• Be properly informed of the nature and risks of the study and given written informed consent.
• Male or female, aged 18 through 65 years (inclusive) with a body mass index (BMI) ≤35 kg/m².
• Subject must meet the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria for current MDD and currently in a moderate to severe major depressive episode (MDE), confirmed using the Mini International Neuropsychiatric Interview (MINI).
• Current MDE duration ≥2 months and <24 months at the time of screening.
• Current illness severity that is at least moderate, defined as a score of ≥20 on the HAM-D17 at screening and on Day 1.
• Score ≥20 on the SHAPS at screening and on Day1.
• Must be willing to comply with the study protocol for the full term of the study.

Key Exclusion Criteria:

• A primary psychiatric diagnosis other than MDD as defined by DSM-5 (comorbid anxiety disorders [including agoraphobia, generalized anxiety disorder, social anxiety disorder, post-traumatic stress disorder (PTSD), and panic disorder] are allowed).
• Concomitant use of antidepressants and/or other disallowed pharmacotherapy (including benzodiazepines).
• History of schizophrenia or other psychotic disorder, MDD with psychotic features, bipolar I or II disorder, or MDD with mixed features.
• History of non-response to >1 antidepressant drug due to lack of efficacy in the current MDE.
• Failing >3 antidepressant drug trials, for any reason, in the current MDE.
• History of non-response to electroconvulsive therapy (ECT) in the past 10 years.
• Active suicidal plan/intent in the past 6 months, or more than 1 lifetime suicide attempt.
• Females who are pregnant, breastfeeding, or planning to become pregnant during the first administration of study drug until 3 months after the last dose of study drug.
• Meets criteria for a substance use disorder within the past 12 months, with the exception of tobacco use, and/or has a positive urine toxicology screen for drugs of abuse.
• Any medical condition or personal circumstance that, in the opinion of the investigator, exposes the subject to unacceptable risk by participating in the study or prevents adherence to the protocol.