At the beginning of the trial, your depression symptoms will be evaluated using two questionnaires. The first is called PHQ-9 (Patient Health Questionnaire-9), which measures depression severity. The second is MADRS (Montgomery-Asberg Depression Rating Scale), another tool to assess depression symptoms. Both assessments will be completed within two weeks before your entry into the study.

Your medical history will be reviewed to confirm that you are currently experiencing your first depressive episode and that you are receiving medication for depression. The review will also verify that you have tried no more than one previous antidepressant treatment.

A blood sample will be collected from you for pharmacogenetic testing. This test analyzes specific genes (CYP3A4, SLC6A4, HTR2A, CYP2D6, CYP2B6, and CYP2C19) that can affect how your body processes antidepressant medications. This genetic information has not been tested for you before.

Based on the study design, you will be assigned to one of two groups. One group will have antidepressant selection guided by the genetic test results along with your demographic, clinical, and other medication information. The other group will receive standard clinical care without genetic testing guidance.

Your treating physician will initiate a new antidepressant treatment following the failure of your previous therapy. The medication selected may be one of the following, taken by mouth: vortioxetine, escitalopram, sertraline, quetiapine, bupropion, clomipramine, venlafaxine, imipramine, fluoxetine, mianserin, duloxetine, agomelatine, amitriptyline, nortriptyline, fluvoxamine, mirtazapine, paroxetine, citalopram, trimipramine, or desvenlafaxine.

The specific medication, dosage, and frequency will be determined by your physician based on your individual clinical situation and, if applicable, your genetic test results. The medication will be provided in various forms such as tablets or capsules, depending on which antidepressant is selected.

You will be monitored for 16 weeks after starting the new antidepressant treatment. During this period, your depression symptoms will be regularly assessed using the PHQ-9 and MADRS questionnaires to evaluate whether your symptoms are improving or if remission has been achieved.

Throughout the 16-week period, any changes to your treatment will be recorded. These changes may include switching to a different antidepressant medication or adjusting the dose of your current medication (either increasing or decreasing it, beyond the usual starting adjustments).

All scheduled clinical visits will take place as planned. Any additional, unscheduled visits to your healthcare provider or psychiatric consultations will also be documented.

If you receive any psychological therapy sessions, such as cognitive behavioral therapy (a type of talk therapy that helps change negative thought patterns) or interpersonal therapy (a therapy focused on improving relationships and communication), these will be recorded.

Any side effects or adverse reactions you experience during the treatment will be monitored and documented. This includes common side effects as well as serious adverse events. Special attention will be given to specific concerns such as suicidal thoughts, suicide attempts, serotonin syndrome (a potentially serious condition caused by too much serotonin in the body), and neuroleptic malignant syndrome (a rare but serious reaction to certain medications).

If you require hospitalization for any reason during the study period, this will be recorded.

If you are a woman of childbearing potential, you will need to continue using highly effective contraception or practice sexual abstinence throughout the study to avoid pregnancy.

At the end of the 16-week follow-up period, a final assessment will be conducted to determine whether your depression symptoms have achieved remission. This will be measured using the same PHQ-9 and MADRS questionnaires used at the beginning of the study.

All information collected during the study, including the number of treatment adjustments, clinical visits, therapy sessions, hospitalizations, and any adverse events, will be compiled for analysis.