Determine The Percentage Of Depressed Outpatients Who Do Not Effectively Metabolize Extended-release Venlafaxine HCl

Inclusion Criteria: * Men and women subjects aged 18 years or older. * Current outpatient treatment with extended-release venlafaxine HCl (U.S. marketed brand Effexor XR®), within the US Food and Drug Administration (FDA)-approved dosage range for depression (37.5 mg/day to 225 mg/day), for 8 weeks or less. * Ability to have a blood draw within 4 to 12 hours of the most recent dose of Effexor XR®. Exclusion Criteria: * Determination by the investigator that a blood draw is contraindicated. * Participation in an investigational study within the past 30 days where the study medication is not known. * Previous treatment with Effexor XR® or extended-release venlafaxine HCl (generic) in the 6 months prior to current treatment regimen. * Treatment with DVS SR within the last 30 days.