Although bipolar disorder has become such a common diagnosis so that overdiagnosis is an issue, clinical research on drug treatment related to bipolar II disorder is still insufficient.
 The Canadian Network for Mood and Anxiety Treatment (CANMAT) guidelines distinguish between bipolar I and II, but the Japanese Society of Mood Disorders (JSMD) and the International College of Neuropsychopharmacology (CINP) guidelines do not. Despite these differences, understanding various guidelines greatly aids psychiatrists in treating bipolar II disorders.
 According to the JSMD guideline, Lithium (Li) is recommended as the first line in any bipolar II phases, quetiapine (QTP) and olanzapine (OLZ) are recommended as first or second line in any phase, and lamotrigine (LTG) is recommended as the first line in the depressive phase and the second line in the maintenance therapy. These drugs are recommended as main medication by JSMD guidelines. According to the CANMAT guidelines, QTP is regarded as the first line in any bipolar II phases, Li is the first or second line in any phase, LTG is regarded as the second line in the depressive phase and the first line in the maintenance therapy, and OLZ is regarded as second line in the manic phase. However, OLZ is not recommended in the depressive phase and maintenance therapy because of insufficient evidence that it is effective in these phases. According to CINP guidelines, QTP is recommended as the first line in any of the bipolar II phases, Li as the first or second line in any phase, but LTG monotherapy is not recommended for up to the third line in all phases. Also, OLZ is recommended for the second line in the manic phase and first line for maintenance therapy, but it is not recommended for up to the third line in the depressive phase. In these three guidelines, Li and QTP are commonly recommended at the upper level in any bipolar II phases, but the position of OLZ and LTG is different in each guideline.
 The use of antidepressants in treating bipolar disorder, especially bipolar II, is a point of controversy among psychiatrists. Therefore, there are differences in opinion among guidelines. JSMD guidelines do not recommend antidepressants. In CANMAT guidelines, new generation antidepressants are recommended for the depressive phase and maintenance therapy as the second and third line. CINP guidelines also recommend additional use of new generation antidepressants as the second line. In recent years, the efficacy and safety of new generation antidepressants have been reported by a number of randomized trials of the bipolar II depressive phase and maintenance therapy. Observing these studies, the use of new generation antidepressants may be effective in treating bipolar II disorder, although the use of antidepressants including new generation antidepressants is not yet recommended in JSMD guidelines.
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