Bipolar disorder is a severe mental health illness characterised by alternating mood swings between highs (mania) and lows (depression). It is not known what causes it except through genetics, stressful life events and chemicals.
Bipolar disorder tends to run in families, suggesting a genetic link. I inherited bipolar disorder from my Grandmother.
Stressful life events and triggers such as relationship breakdowns, stress at college, the loss of a loved one may cause bipolar. Other factors might include overwhelming problems in everyday life, such as problems with money, work or relationships.
Three chemicals - dopamine, norepinephrine and serotonin are thought to be involved in the condition.
The findings on dopamine in mood disorders suggest that decreased dopamine activity is involved in depression, while increased dopamine function contributes to mania. (1)
High and low levels of norepinephrine — also called noradrenaline — are thought to be associated with periods of mania and depressive episodes. (2)
Finally, researchers believe that abnormal functioning of brain circuits that involve serotonin as a chemical messenger contribute to mood disorders (depression and bipolar disorder). It is thought that SSRI antidepressants involve serotonin. (3)
If there's an imbalance in the levels of 1 or more neurotransmitters, a person may develop some symptoms of bipolar disorder. (4)
We still do not understand what causes bipolar, other than through genetics, stressful life events and the role of chemicals. Maybe one day there will be a bipolar pill which will provide monotherapy to all those suffering from bipolar.
1 https://www.sciencedirect.com/science/article/abs/pii/0010440X9290007D#:~:text=The%20findings%20on%20dopamine%20in,dopamine%20function%20contributes%20to%20mania.