Venlafaxine Versus Lamotrigine in the Treatment of Bipolar I/II Depression

Inclusion Criteria: 1. Meets DSM-IV criteria for a diagnosis of Bipolar I disorder, most recent episode depression, or bipolar II disorder, most recent episode depression using the structured clinical interview for DSM-IV Axis 1 disorders 2. Subjects must have a Hamilton depression rating scale score of >16. 3. Patients at visit 1 must have documented trials (levels must be obtained) of their mood stabilizer for at least 2 weeks 4. Subjects must be between the ages of 18-70, male or female 5. Treatment with oral antipsychotics, anticonvulsants or benzodiazepines prior to enrolment or during the study will be permitted, but not other antidepressants. 6. Female patients of childbearing potential must be using a medically accepted means of contraception. 7. Patient is judged by the investigator to be in generally good health 8. Education level and a degree of understanding is such that the patient can communicate effectively with the investigator. 9. Patient must be capable of providing informed consent. Exclusion Criteria: 1. Treatment with antidepressant medication within one day prior to visit 1 or during the protocol. 2. Patients previously showing poor therapeutic response to venlafaxine XR or lamotrigine 3. Judged clinically to be at serious suicidal risk. 4. DSM-IV criteria for substance dependence (except nicotine or caffeine) within the past 30 days 5. Course of ECT (electroconvulsive therapy) in the preceding 4 weeks prior to visit 1 or during the protocol. 6. Patients who suffer from a major neurological or medical illness. 7. Current diagnosis of schizophrenia or other psychotic disorders as defined in the DSM-IV 8. Uncorrected hypothyroidism or hyperthyroidism 9. Female patients who are either pregnant or nursing 10. Elevated thyroid stimulating hormone (TSH).