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