Study Evaluating Safety and Efficacy of Ropanicant in MDD Patients

Inclusion Criteria: * Participants must meet the DSM-5 criteria for MDD without psychotic features and diagnosis confirmed by the Mini-International Neuropsychiatric Interview (MINI). * Participants with a current major depressive episode of at least 4 weeks of duration prior to the screening visit. * Participants must have an MADRS score of ≥25 at the screening and the baseline visits. * Participants must have a score of ≥4 on Clinical Global Impression - Severity (CGI-S) Scale at the screening and the baseline visits. Exclusion Criteria: * Participants who meet criteria for treatment-resistant depression during the current major depressive episode, which will be defined as being non-responders (less than 50% of symptom improvement) to 2 or more depression treatment periods of adequate dose and duration as defined by the Massachusetts General Hospital (MGH) Antidepressant Treatment Response Questionnaire (ATRQ). * Participants taking antidepressant treatment (SSRIs and SNRIs) or any medication that is contraindicated with the use of monoamine oxidase inhibitors (eg, opioids, stimulants) within 2 weeks (or 5 half-lives, whichever is longer) prior to baseline and until the end of study visit. * Participants who do not agree to avoid tyramine rich diet from the start of dosing and until 2 weeks following last study drug administration. * Participants who are habitual smokers or using nicotine products.