Although bipolar disorder (BD) often presents in young adulthood, most individuals experience recurrent mood episodes, psychosocial deficits and high utilization of health services that persist into later life.1 Bipolar depression represents the predominant and least successfully treated phase of this illness. Individuals with BD spend more time ill with depressive symptoms than with manic/hypomanic or with cycling/mixed symptoms,2-4 and the proportion of time spent in depressive episodes to time spent in manic episodes increases with age. The few medications (quetiapine, lurasidone, olanzapine-fluoxetine) FDA-approved for treatment of bipolar depression were studied in predominantly middle-adult-aged cohorts. The clinical management of bipolar disorder in later life is also complicated by medical co-morbidity, cognitive impairment and polypharmacy.5 Furthermore, the neurobiological mechanisms that underlie bipolar depression may change with age and resistance to current treatments is high.6,7 Over the past decade there has been increasing evidence8 that implicates alterations in bioenergetic metabolism and enhanced oxidative stress in the neurobiology of bipolar disorder.9 Although the degree of mitochondrial dysfunction does not produce a substantial systemic metabolic disorder, it is likely sufficient to impact the CNS, as the brain requires twenty-fold the energy production of the rest of the body.9 Furthermore, the efficiency of mitochondrial energy production declines with age, an effect seen both in CNS and peripheral tissue. Successful treatment strategies for late life bipolar disorder may depend on developing novel ways to address reduced mitochondrial ATP (adenosine triphosphate) production. Coenzyme Q10 (CoQ10) is present in the phospholipid bilayers of mitochondria,10 shuttling electrons within the mitochondrial electron transport chain to generate ATP and serving as a potent antioxidant.11 CoQ10has been studied as a treatment for disorders implicating mitochondrial impairment, including congestive heart failure, diabetes, and degenerative neurological conditions.12-15 We now present the results from an open-label study of CoQ10 (added to existing treatment at a dosage of 800 mg/day for 4 weeks) for the treatment of older adults with a current episode of bipolar depression. We hypothesized that CoQ10 would reduce depressive symptoms as measured by the Montgomery Asberg Depression Rating Scale (MADRS).