Effects of Ketamine in the Acute Phase of Suicidal Ideation

Inclusion Criteria:

* French speaking patients freely hospitalized for prevention of suicide and who have a medium or high suicide risk score according to a MINI structured interview
* The patient is able to understand how the study is carried out and the tests performed
* The patient is deemed capable of giving his/her informed consent
* The patient has been correctly informed
* The patient must have given his/her informed and signed consent.
* The patient must be insured or beneficiary of a health insurance plan.
* Presence of suicidal ideation according to the SSI score (score \> 3)
* Negative pregnancy test for women of childbearing age

Exclusion Criteria:

* The patient is participating in another interventional study
* Within the past three months, the patient has participated in another interventional study
* The patient is in an exclusion period determined by a previous study
* The patient is under judicial protection
* The patient is an adult under guardianship
* The patient refuses to sign the consent
* The patient is not able to understand the informed consent
* Pregnancy or breastfeeding
* History of schizophrenia or other psychotic disorders
* Presence of psychotic symptoms at initial interview
* Schizoid or schizotypic personality disorder
* Positive urine screening for illicit substances, excluding cannabis
* Substance dependence in the preceding month (excluding nicotine or caffeine)
* Concomitant treatment with electroconvulsive therapy
* Unstable somatic pathology
* Clinically significant anomalies found during clinical examination, biological test or ECG
* Non-stabilized hypertension or hypertension \> 180/100
* Known or suspected contra-indication for ketamine (includes interactions): hypersensitivity to ketamine, hypertension, class IV cardiac insufficiency, history of stroke, hepatic or cutaneous porphyria, history of intracranial hypertension