Understanding and Treating Suicidal Ideation With Ketamine

Inclusion Criteria: 1. English speaking 2. Ages 18-65 years old 3. Suicidal ideation severity score ≥3 on the Columbia Suicide Severity Rating Scale (C-SSRS) (Baseline/Screening version) at Screening Visit ("active suicidal ideation with any methods") 4. Diagnosis of Major Depressive Disorder (MDD) according to the Diagnostic and Statistical Manual for Mental Disorders 5th Edition (DSM-5) 5. Willing to maintain stable doses of concomitant medications throughout the study 6. Be under the care of a designated health care provider (i.e., family physician or psychiatrist) to follow their care after the completion of the study. Exclusion Criteria: 1. Participants not medically cleared to receive ketamine treatment due to presence of clinically relevant disease (e.g., uncontrolled hypertension, renal or hepatic impairment, significant coronary artery disease, diabetes mellitus, seizure disorder). 2. Known or suspected hypersensitivity or intolerance to ketamine 3. Body mass index (BMI) ≥35 4. History of a primary psychotic disorder (e.g., schizophrenia), or current or recent (\<2 years) acute episode of psychosis 5. Current and/or recent history (\<12 months) of substance use/dependence (except for caffeine or nicotine) or problematic current alcohol use or dependence as defined by DSM-5 criteria 6. Pregnant, breastfeeding or of childbearing potential and unwilling to use an approved method of contraception during the study 7. History of significant head injury including loss of consciousness \>5 minutes 8. Any MRI contraindications 9. Concurrent use of ketamine in any form 10. Concurrent active ECT or repetitive transcranial magnetic stimulation (rTMS) therapy