This is a study to determine the percentage of patients with depression who are treated with extended-release venlafaxine HCl (U.S. marketed brand Effexor XR®) who are Poor Metabolizers (based on the levels of the drug in the blood) at 2D6 (a system in the liver that breaks down some medications and other chemicals).

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.