The modern understanding of bipolar disorder is that it is primarily a biological illness with a genetic component. However, the exact causes of the condition - the things that set it in motion - are not definitively understood at this time. Possible causes being researched include a malfunctioning neurotransmitter (chemical pathway in the brain), a hormonal cause, an infectious agent (bacteria or virus), or an elevated antibody. These possible causes are the subject of widespread debate.
It does appear likely that bipolar disorders result from an imbalance in the body's regulatory systems. The fact that bipolar disorders can typically be controlled by medication strongly suggests that they result from biochemical imbalances. These imbalances most likely occur in the brain and are an indication that a regulatory system has become impaired, or affected, in some way. Although it is thought that bipolar disorders are the result of the body's chemical disturbances, there is no biological diagnostic test to reliably identify the condition. Research in multiple medical disciplines is ongoing in an effort to understand more about bipolar disorders, find dependable diagnostic tools, and develop practical treatments.