Age 12–17 years

Responds ‘yes’ to ASQ at triage, which asks “Are you having thoughts of killing yourself right now?”

Moderate to severe suicidal ideation, defined as score ≥3 on the first 5 questions of the Beck Scale for Suicidal Ideation17

Medically clear (deemed fit for participation in the trial), as judged by the treating physician. Minimum criteria required to be deemed medically clear are:

1. No evidence of serious physical injury requiring urgent intervention

2. 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 postingestion monitoring with no further need for intervention

Acute intoxication, from any substances, including alcohol

Previously enrolled in the current study or currently enrolled in another clinical trial

History of intellectual disability, cognitive developmental delay or autism spectrum disorder by patient/parent report

Active, or history of, psychosis or psychotic disorder

History of non-psychiatric neurological disorder associated with seizures

Any of the following contraindications to ketamine based on the drug monograph:

1. Known allergy or hypersensitivity to ketamine by patient history

2. History of cerebrovascular accident (stroke or aneurysm)

3. History of elevated intracranial pressure or idiopathic intracranial hypertension

4. Significant hypertension requiring daily medication

5. Severe cardiac decompensation

On an involuntary psychiatric hold

Requires physical or chemical restraint

History of violence while in hospital

Pregnant or breastfeeding

Received opioids in the 24 hours prior to study screening