Feasibility of Conducting a Clinical Trial Assessing Efficacy of Lactate as Adjunctive Therapy in Patients With Major Depressive Disorder

Inclusion Criteria: * Study consent signed * 18 ≤ age ≤ 65 years old * Fluent in french * Recently (no more than 1 week) hospitalized for a primary diagnosis of MDD * Current major depressive episode as defined by DSM-5 * Current MADRS score ≥18 * Total number of MDD acute episodes ≤ 3 * Total number of psychiatric medications ≤ 3 at admission * Total number of any medication ≤ 4 at admission * No signs or evidence indicating difficult intravenous access * Willing to hold a peripheral blood catheter for 5 days Exclusion Criteria: * Bipolar depression * History of panic attacks * Severe substance use disorders according to DSM-5-TR criteria * Conditions predisposing to hypernatremia such as: * adrenocortical insufficiency, * diabetes type 1 and insulin-dependent type 2 * extensive tissue injury * Known severe renal insufficiency * Known hepatic insufficiency (impaired lactate metabolism) * Known history of heart failure * Known history of Chronnic Obstructive Pulmonary Disease or respiratory failure * Known hypersentitivity to lactate * Hypernatremia with Na+ \> 150 mmol/L (confirmed on 2 blood withdrawals) * Blood osmolality \> 320 mmol/kg H2O * Hyperlactatemia \> 2 mmol/l * Pregnant or lactating * Forbiden medications : Lithium * Participation to other clinical trials * Any medical conditions that could jeopardize patient's health in case of study participation according to the investigator * Inability to give informed consent (without capacity for discernment) as …