This is a research clinical trial of double-blind, stratified randomized, parallel group, two-centre study. It will be conducted in a total of 250~300 male and female subjects from the Department of Psychiatry at National Cheng Kung University Hospital. Eligible subjects will be psychiatric out- and in-patients, aged between 18~65 years old, who have psychiatric evaluation with clinically suspected of having bipolar II disorder and fulfill the inclusion and exclusion criteria. The add-on double-blind study treatment with dextromethorphan/place will commence at randomization for while patients continue open-label valproate. Subjects will be enrolled for 12 weeks double-blind add-on treatment and randomly assigned to (1) 30mg dextromethorphan+valproate, (2) 5mg memantine+valproate, (3) dextromethorphan+memantine+valproate or (4) placebo+valproate. Concomitant benzodiazepine medication (preferably up to 8mg lorazepam) may be used for daytime sedation, agitation or insomnia during the study. For the consideration of the less influence to immune-system, resperidone 1-3mg/daily and fluoxetine maximum 20mg/daily will be chose. We will measure the treatment response and side effect to clarify the curative effect of DM and memantine add-on therapy to valproate in the treatment of bipolar disorders. This study is being performed to investigate the possibly significant beneficial effects on the subtypes of bipolar disorders psychopathology.

A total of 250~300 male and female subjects from the Department of Psychiatry at National Cheng Kung University Hospital. Eligible subjects who are aged between 18~65 years old and clinically suspected of having bipolar II disorder are invited. The add-on double-blind study treatment with dextromethorphan/place will commence at randomization for while patients continue open-label valproate. Subjects will be enrolled for 12 weeks double-blind add-on treatment and randomly assigned to (1) 30mg dextromethorphan+valproate, (2) 5mg memantine+valproate, (3) dextromethorphan+memantine+valproate or (4) placebo+valproate. Concomitant benzodiazepine medication (preferably up to 8mg lorazepam) may be used for daytime sedation, agitation or insomnia during the study. For the consideration of the less influence to immune-system, resperidone 1-3mg/daily and fluoxetine maximum 20mg/daily will be chose. We will measure the treatment response and side effect to clarify the curative effect of DM and memantine add-on therapy to valproate in the treatment of bipolar disorders. This study is being performed to investigate the possibly significant beneficial effects on the subtypes of bipolar disorders psychopathology.

Inclusion Criteria:

• A 2-day minimum for hypomania to diagnose bipolar II disorder
• A total of Hamilton Rating Scale for Depression scored at least 18 or Young Mania Rating Scale scored at least 14 at the screening stage
• Must allow to ensure acceptable compliance and visit

Exclusion Criteria:

• Pregnant females or nursing
• Women of childbearing potential not using adequate contraception
• Received dextromethorphan, memantine, other antiinflammatory medication within 1 week prior
• Clinically significant medical condition (cardiac, hepatic and renal disease)
• Received electroconvulsive therapy patients within 4 weeks prior to the first dose of double-blind medication
• Increase in total SGOT, SGPT, BUN and creatinine by more than 3X upper limit of normal.