The concept of bipolar disorder has undergone a transformation over the last two decades. Once considered a rare and serious mental disorder, bipolar disorder is being diagnosed with increasing frequency in Europe and North America, and is suggested to replace many other diagnoses. The current article shows how the modern concept of bipolar disorder has been created in the course of efforts to market new antipsychotics and other drugs for bipolar disorder, to enable these drugs to migrate out of the arena of serious mental disorder and into the more profitable realm of everyday emotional problems. A new and flexible notion of the condition has been created that bears little resemblance to the classical condition, and that can easily be applied to ordinary variations in temperament. The assertion that bipolar disorder is a brain disease arising from a biochemical imbalance helps justify this expansion by portraying drug treatment as targeted and specific, and by diverting attention from the adverse effects and mind-altering properties of the drugs themselves. Childhood behavioural problems have also been metamorphosed into "paediatric bipolar disorder," under the leadership of academic psychiatry, with the assistance of drug company financing. The expansion of bipolar disorder, like depression before it, medicalises personal and social difficulties, and profoundly affects the way people in Western nations conceive of what it means to be human.