This is an open-label flexible-dose pilot study evaluating the efficacy, safety, and tolerability of Pristiq (desvenlafaxine) in outpatient subjects diagnosed with Generalized Anxiety Disorder (GAD) with or without comorbidities that are secondary to the GAD. Primary trial objective is to evaluate the efficacy of Pristiq (desvenlafaxine) SNRI treatment 50 to 100 mg once daily in the treatment of GAD with or without comorbidities. Secondary trial objective is to determine whether or not treatment outcome in GAD is related to changes in cortical prefrontal activity of norepinephrine.