The Mayo Clinic Pharmacogenomic Research Network Antidepressant Medication Pharmacogenomic Study (PGRN-AMPS) was supported by the NIGMS-Pharmacogenomics Research Network (PGRN), which has been described elsewhere.12 (link), 13 The PGRN-AMPS is an ongoing eight week outpatient SSRI clinical trial that was performed at the Mayo Clinic in Rochester, MN. Patients enrolled in the study met diagnostic criteria for MDD without psychosis or mania and had a 17-item Hamilton Depression Rating Scale (HAMD-17) score ≥14. The study was designed with inclusion and exclusion criteria similar to those used in the Sequenced Treatment Alternatives to Relieve Depression study (STAR*D).14 (link) Potential study subjects taking an antidepressant, antipsychotic or mood stabilizing medication were not eligible for enrollment. Patients with MDD initially received either 10 mg of escitalopram or 20 mg of citalopram. SSRI efficacy was determined using the 16-item Quick Inventory of Depressive Symptomatology (QIDS-C16) scores after four weeks and then eight weeks of SSRI therapy. At four weeks after the initiation of treatment, the dose could be increased to 20 mg of escitalopram or 40 mg of citalopram after a clinical assessment of the subject. Unless there was a contraindication, dose was increased if the QIDS-C16 score at the follow-up visit was ≥9, and possibly following a clinical evaluation if the score was between 6 and 8. The dose could also be decreased, or treatment could be discontinued, if a patient developed persistent side effects. Blood samples were obtained at baseline for DNA extraction, and then again at weeks four and eight for assays of drug and metabolite levels. All patients provided written informed consent. The study protocol was approved by the Mayo Clinic Institutional Review Board.