Ink and watercolour illustration depicting the two mood phases common in bipolar disorder

Understanding bipolar disorder

Read our Q&A to find out more about this commonly misunderstood condition

How many people in the UK have bipolar disorder?

Over 250,000 people in the UK are diagnosed with bipolar disorder.

How many people in the world have bipolar disorder?

About 1 per cent of the population in most countries in the world – around 51 million people worldwide – are living with the disorder.

What is it? What do we know about it?

As its name suggests, people with bipolar disorder have moods that swing between two opposite extremes (or poles): from high to low. The highs are what make a diagnosis of bipolar disorder possible. In these moods of intense excitement and agitation people start speaking faster and sleeping less, their thoughts race, they get distracted easily, and they may start acting recklessly, by driving too fast, overspending or taking drugs.

If this behaviour is extreme – or if it includes symptoms of psychosis such as hallucinations and delusions, for example of grandeur or persecution (some people in the ‘high’ phase of bipolar disorder become grandiose and euphoric, whereas others may become irritable and paranoid) – it is called mania. An episode of mania may lead to a diagnosis of bipolar I disorder. If the symptoms are milder and there is no sign of psychosis the episode is called hypomania, and may lead to a diagnosis of bipolar II disorder.

In both cases the ‘highs’ are usually interspersed with periods of equally intense low mood – depression that can become so debilitating that this disorder puts people at greater risk of suicide than any other illness.

Both bipolar I and II lie on a spectrum including many other subtypes. Rapid-cycling bipolar disorder is diagnosed when someone has four or more mood episodes (mania, hypomania or depression) within one year. Seasonal bipolar disorder occurs at particular times of the year (the chance of onset increases in spring when a rapid increase in hours of sunshine is thought to affect the pineal gland). The cyclothymic type describes hypomanic episodes with briefer periods of depression than the full-blown episodes seen in other bipolar subtypes. And people with the mixed type experience symptoms of depression like anxiety and guilt during a manic phase.

Untreated, this can be a progressive illness. Every high and low takes a hit on the brain, increasing the risk of another episode and reducing responsiveness to treatment. This can lead to progressive deterioration of functional and cognitive abilities, although this is not the case for everyone with bipolar disorder. One of the challenges can be to convince someone who is experiencing the euphoria of a high that they have a disease that may come back, could damage their brain, and quite possibly drive them to suicide, drugs or alcohol if they don’t get it treated.

What do scientists think is happening in the brain?

Scientists believe bipolar disorder is partly caused by an imbalance of neurotransmitters like serotonin and dopamine in the brain. Researchers believe abnormal serotonin chemistry, which plays a critical role in sleep, wakefulness, eating, impulsivity and mood, has a feedback effect on other brain chemicals, causing mood changes. And disruption to the dopamine system (responsible for feelings of pleasure and euphoria) could lead to the psychosis seen in mania. More recently, variation in the GABA and glutamate neurotransmitter systems has also been shown to be associated with bipolar disorder. (See our drugs and the brain article for more information on these neurotransmitters.)

How is it treated?

Bipolar disorder is generally treated using a combination approach to address current symptoms as well as prevent future episodes.

The most common medicines are mood stabilisers, which are taken every day. The gold standard since 1970 has been lithium, although it doesn’t work for everyone.

Atypical antipsychotics like olanzapine and risperidone or anticonvulsants like carbamazepine and divalproex are also effective in treating mania and maintaining a stable mood.

Talking treatments like cognitive behavioural therapy (CBT) and relapse prevention can help people manage their own symptoms. Psycho-education for bipolar disorder helps individuals to understand their illness, learn to recognise the early warning signs of highs and lows, and develop the skills to stay as well as possible. Lifestyle advice regarding, for example, the importance of regular sleep, routines, avoiding stress and monitoring alcohol intake is also key to staying well.

What don’t we know?

Many, many questions about bipolar disorder – including its causes and how or why particular treatments work – remain unanswered. Genetic factors have been shown to influence an individual’s risk of developing bipolar disorder and may be relevant for around 80 per cent of cases, but researchers still have to unravel the specific roles of the many different genes involved.

We don’t yet understand why lithium is so effective in some people but not in others, although recent research suggests an enzyme called prolyl oligopeptidase (PO) might influence sensitivity to the drug.

We also don’t know why the disorder is appearing at an increasingly early age – whether this is because people were underdiagnosed before, or due to changing social and environmental factors.

Is it hereditary?

Bipolar disorder does seem to run in families. If you have one parent or a non-identical twin with the disorder you have a 10 to 25 per cent chance of developing it yourself. With two bipolar parents or an identical twin that goes up to 40 per cent and 70 per cent respectively. These percentages are high, but it’s important to remember that there is still also a good chance you won’t necessarily get the disorder.

Genes aside, physical factors like stress, hormonal changes in pregnancy or too much caffeine or substance abuse can activate the disorder if it is lying dormant, or bring on and exacerbate a manic or depressive episode. And life events – positive or negative – such as a job loss, an exam or a success, can tip someone prone to bipolar disorder into the depths of despair or the giddy heights of euphoria.

What organisations can help?

Mind (local)

A network of over 150 local services across England and Wales, including supported housing, crisis helplines, drop-in centres, employment and training schemes, counselling and befriending.

Bipolar UK


Depression Alliance

Tel: 0845 123 2320



Tel: 0845 790 9090 (ROI: 1850 609 090)


Bipolar Fellowship Scotland

Tel: 0141 560 2050

Journeys – towards recovery from depression [Welsh service]

Tel: 029 2069 2891


Lead image:

Ink and watercolour illustration depicting the two mood phases common in bipolar disorder.

Stephen Magrath/Wellcome Images CC BY NC ND


Further reading

About this resource

This resource was first published in ‘Thinking’ in August 2014.

Neuroscience, Psychology, Medicine
Education levels:
16–19, Undergraduate, Continuing professional development