Study of IV Ketamine for Emergency Department Treatment of Adolescent Suicidal Ideation

Inclusion Criteria: 1. Responds "yes" to Ask Suicide Screening Question (ASQ) #5 at triage, which asks; "Are you having thoughts of killing yourself right now?" 2. Moderate to severe suicidal ideation, defined as score ≥ 3 on the first 5 questions of the Beck Scale for Suicidal Ideation (SSI5) 3. Age 12 to 17 years, inclusive 4. Medically clear (deemed fit for participation in the trial), as judged by the treating physician. Minimum criteria required to be deemed medically clear are: a) No evidence of serious physical injury requiring urgent intervention b) No evidence of acute ingestion requiring monitoring, blood tests, imaging or ECG or in the context of acute ingestion they have satisfied the requisite number of hours of post-ingestion monitoring with no further need for intervention. Exclusion Criteria: 1. Acute intoxication from any substance, including alcohol 2. Previously enrolled in the current study or currently enrolled in another clinical trial 3. History of intellectual disability or autism spectrum disorder by patient/parent report 4. Active, or history of, psychosis or psychotic disorder 5. History of non-psychiatric neurologic disorder (e.g., epilepsy) 6. Any of the following contraindications to ketamine based on the drug monograph: a) Known allergy or hypersensitivity to ketamine by patient history b) History of cerebrovascular accident (stroke or aneurysm) c) History of elevated intracranial pressure or idiopathic intracranial hypertension d) Significant hypertension requiring daily medication e) Severe cardiac decompensation 7. On an involuntary psychiatric hold 8. Requires physical or chemical restraint 9. History of violence while in hospital 10. Pregnant or breastfeeding 11. Received opioids in the 2-hours prior to study screening