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Bipolar disorder

The exact cause of bipolar disorder is unknown.

Many factors may play a role, such as physical, environmental and social factors.

A complex mix of these may work together to make a person more likely to develop the condition.

Chemical imbalance in the brain

Many experts put bipolar disorder down to low or high levels of chemicals in the brain.

The chemicals that control the brain are neurotransmitters.

Neurotransmitters include:

  • noradrenaline
  • serotonin
  • dopamine

An imbalance in the levels of one or more may lead to you developing some symptoms of bipolar disorder. 


It's also thought bipolar disorder is linked to genetics. This is because the condition seems to run in families. Family members of a person with the condition have an increased risk of developing it. But no single gene causes bipolar disorder.

If bipolar runs in a family, genetic and environmental factors that can act as triggers for other family members.


A stressful circumstance or situation often triggers the symptoms of bipolar disorder. Examples of stressful triggers include:

  • the breakdown of a relationship
  • physical, sexual or emotional abuse
  • the death of a close family member or loved one

These types of events can cause episodes of depression at any time in a person's life.

Bipolar disorder may also be triggered by:

  • physical illness
  • medications used to treat physical illness, for example high-dose steroids
  • sleep disturbances
  • overwhelming problems in everyday life – such as problems with money, work or relationships
  • childhood trauma

Using drugs like MDMA, LSD or cocaine may trigger an episode, which can mimic an episode of mania.

Content supplied by the NHS and adapted for Ireland by the HSE.

page last reviewed: 04/10/2018
next review due: 04/10/2021

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