This review introduces the treatment guidelines of acute mania by the Japanese Society of Mood Disorders (JSMD) and compares it with that of the Canadian Network for Mood and Anxiety Treatments (CANMAT). Lithium alone for mild mania and the combination of lithium and some atypical antipsychotic drugs for more severe mania are recommended by the JSMD guidelines. This recommendation is different from that of the CANMAT. As maintenance treatment after treatment of the acute phase should be considered from the start of treatment and lithium is the most recommended drug for maintenance treatment in the JSMD guideline, lithium becomes the critical drug for the treatment of mania in the JSMD guidelines. The so-called "drug lag" accounts for the difference between the two guidelines. Safer drugs for extrapyramidal symptoms and cognitive function should be preferred, because these adverse effects interfere with the functional recovery of bipolar patients. The adverse effects of hypnotics or alcohol on cognitive function should be noted carefully, because cognitive impairment influences disabilities and quality of life (QOL) in bipolar patients. New understanding of the pathophysiology of bipolar disorder, that is circadian rhythm dysfunction, may lead to its new diagnosis and treatment.