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

The goal of this clinical trial is to test the efficacy of lactate (a natural substance) in combination with standard antidepressant treatment, in patients hospitalized for a major depressive episode. The main question\[s\] it aims to answer are: * does lactate diminishes depression severity when administered in combination with antidepressant ? * is it feasible to test lactate treatment in a large-scale clinical trial ? Participants will receive lactate intravenously daily (20 min infusion) for 5 days during hospitalisation (together with the standard antidepressant treatment). Researchers will compare with a group receiving a placebo instead of lactate to see if lactate has antidepressant effects.