According to the US government's National Institute of Mental Health (NIMH), "There is no single cause for bipolar disorder—rather, many factors act together to produce the illness." "Because bipolar disorder tends to run in families, researchers have been searching for specific genes—the microscopic "building blocks" of DNA inside all cells that influence how the body and mind work and grow—passed down through generations that may increase a person's chance of developing the illness." "In addition, findings from gene research suggest that bipolar disorder, like other mental illnesses, does not occur because of a single gene."
It is well established that bipolar disorder is a genetically influenced condition which can respond very well to medication.
Psychological factors also play a strong role in both the psychopathology of the disorder and the psychotherapeutic factors aimed at alleviating core symptoms, recognizing episode triggers, reducing negative expressed emotion in relationships, recognizing prodromal symptoms before full-blown recurrence, and, practicing the factors that lead to maintenance of remission. Modern evidence based psychotherapies designed specifically for bipolar disorder when used in combination with standard medication treatment increase the time the individual stays well significantly longer than medications alone. These psychotherapies are Interpersonal and Social Rhythm Therapy for Bipolar Disorder, Family Focused Therapy for Bipolar Disorder, Psycho education, Cognitive Therapy for Bipolar Disorder, and Prodrome Detection. All except Psycho education and prodrome detection are available as books.
Brain scientist Husseini K. Manji M.D. of the NIMH states that at their most basic level, the bipolar disorders involve problems in brain structure and function. He stated that these structural changes respond very well to treatment with lithium and valproate in a University of California, Los Angeles Neuropsychiatric Institute (NPI) Grand Rounds Talkgiven in 2003
Early in the course of the illness brain structural abnormalities may lead to feelings of anxiety and lower stress resilience. When faced with a very stressful, negative major life event, such as a failure in an important area, an individual may have his first major depression. Conversely, when an individual accomplishes a major achievement he may experience his first hypomanic or manic episode. Individuals with bipolar disorder tend to experience episode triggers involving either interpersonal or achievement-related life events. An example of interpersonal-life events include falling in love or, conversely, the death of a close friend. Achievement-related life events include acceptance into an elite graduate school or by contrast, being fired from work.
Veteran brain researcher Robert Post M.D. of the U.S. NIMH proposed the "kindling" theory which asserts that people who are genetically predisposed toward bipolar disorder experience a series of stressful events, each of which lowers the threshold at which mood changes occur. Eventually, the mood episode starts (and becomes recurrent) by itself. Not all individuals experience subsequent mood episodes in the absence of positive or negative life events, however.
Individuals with late-adolescent/early adult onset of the disorder will very likely have experienced childhood anxiety and depression. Childhood onset bipolar disorder should be treated early because according to Joseph Calabrese of Case Western Reserve University, childhood forms of the illness may be easier to treat than adult forms of the illness.
It is becoming increasingly clear that bipolar and unipolar mood disorders have a genetic component. For example, a family history of bipolar spectrum disorders can impart a genetic predisposition towards developing a bipolar spectrum disorder. Since bipolar disorders are polygenic (involving many genes), there are apt to be many unipolar and bipolar disordered individuals in the same family pedigree. This is very often the case. Anxiety disorders, clinical depression, eating disorders, premenstrual dysphoric disorder, postpartum depression, postpartum psychosis and/or schizophrenia may be part of the patient's family history and reflects a term called "genetic loading".
Bipolar disorder is more than just biological and psychological. Since "many factors act together to produce the illness", bipolar disorder is called a multi factorial illness, because many genes and environmental factors conspire to create the disorder.
Since bipolar disorder is so heterogeneous, it is likely that people experience different pathways towards the illness.
Recent research done in Japan indicates that bipolar disorder can be comprehensively explained by a hypothesis of dysfunctional mitochondria in the brain