Researchers looking into the possible causes of bipolar disorder agree that there are a number of factors that act together to cause the disorder. Despite the large amount of information, there is no single conclusive theory. Following are some of the theories about the causes of the condition.

Family history/genetic causes

There is sound evidence from studies of families and twins to indicate that bipolar disorder (and depression) are partly inherited. The chance that a relative of someone with bipolar disorder will develop bipolar disorder is 3-15%. Children, with one parent bipolar, have approximately a 25% chance of developing a mood disorder (not necessarily bipolar disorder). The risk rises to about 50% if both parents have the condition.

Some idea of risk can be obtained by taking a family history. Risk can be estimated by assessing the number of people in the family with bipolar disorder, and the closeness of their biological/genetic relationship to the person concerned. It is important to realize that just because one family member has bipolar disorder, it does not necessarily mean that all family members will inherit it. There may be a tendency to develop the illness, but there are other factors that must also be considered. No single 'bipolar gene' has been identified, and there is no test that can be done to estimate the likelihood that a person will develop the condition.

Brain chemicals

Older chemical theories as to the causes of bipolar disorder involve neurotransmitters called catecholamines - namely nor-adrenaline and dopamine. Their chemical structures are similar. The catecholamine hypothesis therefore suggests, put simply, that mania is due to too much catecholamine and depression to too little catecholamine in the brain.

A more recent theory, while not completely overturning the catecholamine hypothesis, is that serotonin (an indolamine) is more important, and that abnormalities in serotonin chemistry in the brain cause these mood swings because of the feedback effects that serotonin has on other brain chemicals.

Brain anatomy

Using specialized brain-imaging techniques, a number of changes in the brains of people with bipolar disorder have been found, however, these results are not consistent or definite enough for brain scanning to be of help in diagnosing the condition at the present time.

Environmental factors

Researchers are not convinced that bipolar disorder, and the associated mood states, are triggered by environmental factors such as distressing life events (e.g. the death of a loved one, divorce or work/study problems). An episode can occur without any obvious stress, but even so, there are benefits for a person with bipolar disorder to learn about ways to reduce and manage stress in their life, and to cope with the illness itself.

Medical illness

Medical illnesses do not cause bipolar disorder, but are well known to cause symptoms that can be easily confused with the condition. A number of medications, metabolic disturbances, neurological conditions, infections and brain tumours can cause manic and hypomanic symptoms. Special tests can exclude these conditions.

Other theories

Research is continuing into other theories that involve different neurotransmitters, the endocrine and the immune systems, and abnormalities of circadian rhythm (the sleep-wake cycle).