The purpose of this study is to evaluate the effectiveness and tolerability of an investigational drug for the treatment of manic episodes of bipolar disorder. The investigational drug will be given as additional treatment with either lithium or valproate, which are already FDA (Food and Drug Administration)-approved treatments for mania.

Inclusion Criteria:

• Diagnosis of bipolar disorder (type I) with manic or mixed episodes (including patients with/without psychotic features or with/without a history of rapid cycling)
• In need of psychiatric treatment
• Cooperation and willingness to complete all aspects of the study

Exclusion Criteria:

• Current diagnosis other than bipolar I disorder
• History of schizophrenia or schizoaffective disorder
• Drug dependence within 1 month prior to study start or testing positive in a urine drug test
• Suicide attempt within 1 month prior to study start or at immediate risk of harm to self or others
• Any form of psychotherapy within 1 month prior to study start