Bipolar Disorder with Comorbid Substance Use Disorder in a Young Male not Responding to Combination Therapy: Endoxifen Use for 2 Years

Abstract: Impulsivity is common to both bipolar disorder (BD) and substance use disorder (SUD). Bipolar disorder is in fact a risk factor for SUD, wherein substances may be used to achieve symptom relief. Impulsivity is associated with excessive protein kinase C (PKC) activity, and is implicated in the development of BD. This case report describes the use of endoxifen, a direct PKC inhibitor, for the management of a young male with BD and SUD who was not responsive to combination therapy with pharmacotherapies including lithium, haloperidol, and risperidone. The inclusion of endoxifen in the treatment regimen while discontinuing haloperidol and tapering of the dose of lithium led to reduced substance use and improvement of the symptoms of bipolar I mania within 3 weeks. The patient tolerated the treatment well, including long-term use for 2 years. Therefore, the utility of endoxifen in the management of SUD could be explored in larger studies.