This study will assess the effectiveness of venlafaxine XR in preventing the relapse of generalized anxiety disorder after 6 months of treatment versus 12 months of treatment.

Generalized anxiety disorder (GAD) is a highly prevalent, chronic psychiatric disorder. Despite the fact that GAD frequently demands prolonged treatment with medication, very little is known about the benefits of long-term treatment. GAD is characterized by 6 months or more of exaggerated worry and tension that is unfounded or much more severe than the normal anxiety most people experience. People with GAD are unable to relax and often suffer from insomnia. Venlafaxine XR, a drug used to treat depression, has been shown to be effective in the short-term treatment of GAD. However, its benefits over a course of more than 8 weeks have not been assessed. This study will evaluate the effectiveness of venlafaxine XR in treating GAD on a long-term basis and preventing the relapse of GAD after 6 months of treatment versus 12 months of treatment.

Participants in this double-blind study will first receive 6 months of open-label treatment with venlafaxine XR. Upon completion of this initial phase, participants will be randomly assigned to either continue on venlafaxine XR or begin taking placebo. After 12 months, participants taking venlafaxine XR will be randomly assigned to continue on the drug or switch to placebo. Participants will have 22 study visits over at least 18 months. Follow-up visits will occur 24 months after enrollment. Relapse of GAD will be assessed with the Hamilton Anxiety Scale and Global Severity and Improvement Scale. A variety of methods, including questionnaires and standardized scales, will be used to assess secondary outcomes.

Inclusion Criteria:

• GAD diagnosis by structured interview
• Hamilton Anxiety Scale score of 18 or less
• Clinical Global Impressions Scale score of at least 4
• Hamilton Depression Scale score of 18 or less
• Hamilton Depression Scale suicide item score less than 2
• Use of an effective form of contraception throughout the study

Exclusion Criteria:

• Hypersensitivity to venlafaxine XR
• History of seizures
• Episode of major depressive disorder in the previous 6 months
• History of any psychotic illness, bipolar disorder, or dementia
• Substance abuse and dependence during the past 6 months
• Other anxiety disorders with the exception of social phobia as long as GAD is primary
• Regular use of anxiolytics or antidepressants within 7 days of study onset
• Use of fluoxetine or monoamine oxidase inhibitors within 28 days of study onset (low dose usage of benzodiazepines will not prevent participation)
• Use of other psychotic medication besides benzodiazepines during the study