In this study at the Solothurn Psychiatric Clinic, the investigators compare the effectiveness and tolerability of antidepressant pharmacotherapy in three groups. In the intervention group, the physician selects and doses the medication for depression based on a pharmacogenetic examination conducted by a clinical pharmacist. In the standard group, the treating physician selects and doses the antidepressant drug without the support of genetic testing, in accordance with current standard practice. If after the first week of hopsitalization no adjustment to a new antidepressant is necessary, the investigators will monitor the progress of these patients until they leave the clinic in an observational arm. The drugs used are all approved in Switzerland for the treatment of depression. Classification into the intervention or standard group is made randomly after the first week of hospitalisation, if the treating physician deems it necessary to change or readjust the antidepressant pharmacotherapy. The probability of allocation to one of the two study groups is 50%. All study participants will be hospitalized for at least five weeks and monitored until they leave the clinic. In total, it is planned to include and examine 95 patients each into the intervention and standard group.

Inclusion Criteria:

• ≥ 18 years old
• Diagnosis unipolar moderate or severe depressive episode or recurrent depressive disorder (ICD10: F32.1/32.2/33.1/33.2)
• HAM-D17 ≥ 17

Exclusion Criteria:

• Acute suicide risk
• Psychotic symptomatology
• Other acute serious psychiatric disorder other than depression
• Excessive consumption of alcohol and/or drugs
• Severe acute - or severe chronic somatic diseases
• Pregnant / lactating women
• Under current treatment with fluoxetine