躁郁症（英语：bipolar disorder，亦称双极性情感疾患，早期称为躁狂抑郁疾病），是一种精神疾病，特征为患者会经历情绪的亢奋期和抑郁期。情绪亢奋期（躁期）可分为「狂躁」或是「轻躁狂」，两者的区别在于是否影响生活及工作和是否出现精神病症状。于狂躁期，患者感到或表现出异常开心、有活力、易怒，常会做出不计后果的决定，对睡眠的需求也往往会减少。于抑郁期，患者会哭泣、缺乏与他人眼神交流、对生命萌生负面看法，也有自杀的可能。病史长达20年以上的患者，其自杀风险超过6%，自残风险则约30-40%。躁郁症也常伴随焦虑症以及药物滥用等心理问题。

Bipolar disorder, also known as manic depression, is a mental illness characterized by periods of depression and periods of elevated mood. The elevated mood is significant and is known as mania or hypomania, depending on its severity, or whether symptoms of psychosis are present. During mania an individual behaves or feels abnormally energetic, happy or irritable. Individuals often make poorly thought out decisions with little regard to the consequences. The need for sleep is usually reduced during manic phases as well. During periods of depression there may be crying, a negative outlook on life, and poor eye contact with others. The risk of suicide among those with the illness is high at greater than 6 percent over 20 years, while self-harm occurs in 30-40 percent. Other mental health issues such as anxiety disorder and substance use disorder are commonly associated.