Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of depression and periods of abnormally elevated mood that each last from days to weeks. If the elevated mood is severe or associated with psychosis, it is called mania; if it is less severe and does not significantly affect functioning, it is called hypomania. During mania, an individual behaves or feels abnormally energetic, happy or irritable, and they often make impulsive decisions with little regard for the consequences. There is usually also a reduced need for sleep during manic phases. During periods of depression, the individual may experience crying and have a negative outlook on life and poor eye contact with others. The risk of suicide is high; over a period of 20 years, 6% of those with bipolar disorder died by suicide, while 30–40% engaged in self-harm. Other mental health issues, such as anxiety disorders and substance use disorders, are commonly associated with bipolar disorder.

द्रिध्रुवी विकार एक गंभीर प्रकार का मानसिक रोग है जो एक प्रकार का मनोदशा विकार है। इस रोग से ग्रसित रोगी की मनोदशा बारी-बारी से दो विपरीत अवस्थाओं में जाती रहती है। एक मनोदशा को सनक या उन्माद और दूसरी मनोदशा को अवसाद कहते हैं। सनक की मनोदशा में रोगी अति-आशावादी हो सकता है; अपने बारे मे बढ़ी-चढ़ी धारणा रख सकता है ; व्यक्ति अति-क्रियाशील हो सकता है ; रोगी सोना नहीं चाहता या सोने को अनावश्यक कहता है आदि। दूसरी तरफ अवसाद की मनोदशा में रोगी उदास रहता है; उसको थकान लगती है; अपने को दोषी महसूस करता है या उसमें आशाहीनता दिखायी देती है।