The purpose of this study is to determine if lamotrigine add-on therapy is associated with decreased cocaine craving and improvement in depressive symptom severity than placebo in a group of outpatients with bipolar disorder and cocaine dependence. Additionally, this study is examining whether lamotrigine add-on therapy is associated with decreased cocaine use and the improvement of manic symptom severity than placebo in a group of outpatients with bipolar disorder and cocaine dependence.