Introduction

Depression is the most common mood state among individuals with Bipolar II (BP II) Disorder. Indeed, much of the historical under-recognition of bipolar illness, and its misdiagnosis as unipolar disorder, stems from the overwhelming predominance and severity of depressive rather than manic symptoms. As described in Chapter 4, depression, far more than hypomania, accounts for the excess morbidity, functional disability and mortality from suicide in BP II patients. Because hypomanic periods are by definition non-disabling, with symptoms often ego-syntonic to patients, clinicians and patients alike often fail to distinguish BP II depression from unipolar depression. Differences in medication response, course, prognosis and outcome of unipolar versus BP II depression make this nosologic distinction far from academic. Hence, the optimal strategy for BP II depression assumes particular importance.

Traditional antidepressants represent the most obvious and relevant pharmacotherapy strategy for BP II depression, although clinical practice relies heavily on assumptions and inferences from the treatment of unipolar depression, and even Bipolar I Disorder (BP I) depression – rightly or wrongly – to guide decision-making. Choosing to treat BP II depression with antidepressants hinges on the two most fundamental concerns of any medical intervention: is it safe? And, is it effective? Moreover, because alternative pharmacotherapy strategies exist to treat bipolar depression, as discussed in other chapters, it is worthwhile first to consider the existing evidence, gaps in evidence, and clinical judgements that can best inform decisions about when antidepressants should (and should not) be used.