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Differentiating Between Bipolar Disorder and Borderline Personality Disorder

In the United Kingdom, around 1.3 million people are affected by bipolar disorder (BD), which is around one in fifty people. It is one of the most common long-term conditions, affecting more people than epilepsy and autism spectrum disorder. Borderline personality disorder (BPD), on the other hand, affects around 0.7% of people generally in the UK. However, it’s also thought to be under-recognised.

These two conditions are distinct from one another yet share mood disturbances as their most prominent symptoms, which is why they are often misunderstood. It is their origins, diagnostic criteria and treatments that set them apart. Understanding the nuances of the two is important for those with one of the conditions as well as their loved ones supporting them.

Understanding bipolar disorder (BD)

Bipolar disorder (BD) is a psychiatric condition affecting a person’s mood. It is characterised by extreme moods that swing from mania to depression. This condition used to be called manic depression. 

The depressive episodes of bipolar disorder are characterised by feelings of lethargy and low mood. Conversely, the episodes of hypomania are characterised by being overactive and feeling euphoric. The symptoms of the condition will depend upon the type of episode the individual is currently experiencing. 

The mood swings associated with bipolar disorder are extreme. Unlike mood swings experienced by the general population, the episodes of bipolar disorder can last weeks or more. 

The causes of bipolar disorder

There isn’t a definitive cause of bipolar disorder. It is believed that a number of factors influence the development or exacerbation of the condition. These can be physical, social and environmental factors.

These include:

  • Genetics: Bipolar disorder seems to run in families. However, no gene has been identified. It is believed that you can be genetically predisposed but there are other factors that are at play (environmental/social) that can be triggers.
  • Triggers: Triggers of bipolar disorder include relationship breakdowns, abuse (emotional, physical or sexual), experiencing a death, physical illness, sleep problems, and problems with money or work.
  • Chemical imbalances: Bipolar disorder is also thought to be linked to imbalances of key neurotransmitters like dopamine, serotonin and noradrenaline.

Who does bipolar disorder affect?

This is a fairly common disorder. Although it can occur at any age, it often manifests in late adolescence and early adulthood. Both men and women are equally affected.

Bipolar Disorder and Borderline Personality Disorder

Understanding borderline personality disorder (BPD)

Borderline personality disorder also affects a person’s mood. However, unlike bipolar disorder, it also affects how they interact with other people. This is the most well-known personality disorder

Generally speaking, a person with a diagnosed personality disorder will have differences in how they feel, think and relate to other people. 

Causes of borderline personality disorder

Like bipolar disorder, there isn’t a definitive cause for borderline personality disorder and it is thought to be caused by many factors at play. These include:

  • Genetics: Your genes can make you more susceptible to developing borderline personality disorder.
  • Brain chemical imbalances: Altered levels of serotonin and other neurotransmitters are likely at play in BPD.
  • Altered brains: Many individuals with BPD have been shown to have altered brain structures in their amygdala, hippocampus and orbitofrontal cortex. These play a role in emotions, behaviour and self-control, and decision-making, respectively.
  • Environmental factors like abuse, long-term exposure to distress or fear, neglect, and growing up with unstable parents (e.g., due to alcohol, drugs or a serious mental health condition) are thought to contribute to the development of BPD.

Overlapping symptoms

There are some symptoms in common between BPD and BD. These are:

  • Mood instability: Both disorders feature intense moods and mood changes. In BPD these are rapid; in BD these are more prolonged episodes.
  • Impulsivity: Both conditions have an element of impulsivity. This might mean individuals engage in risky behaviours, impulsive spending or substance abuse. However, the reasons for the impulsivity are different.
  • Relationship problems: Both conditions mean that people struggle to maintain stable relationships due to intense emotions and mood swings.
  • Emotional dysregulation: This is a core feature in both conditions. Individuals struggle to manage and control their emotions.
  • Depressive symptoms: Both disorders feature symptoms like sadness, changes in appetite, feelings of hopelessness and loss of interest.
  • Self-harm and suicidal ideation: Both BPD and BD are often associated with an increased risk of suicidal ideation and self-harming behaviours.

Key differences

While there are clear overlaps in the conditions in terms of the symptoms, these are distinct mental health conditions that have differences. Here are the separating factors:

Mood swings

In bipolar disorder there are distinct episodes of depression and mania, which can last days, weeks or months. There may be periods of stable mood in between. With borderline personality disorder, mood swings occur rapidly as they’re triggered by stressors. Mood shifts are intense but not prolonged like in BD.

Duration and frequency of symptoms

Bipolar disorder episodes are distinct periods and can last months. They are prolonged. In BPD, a range of mood events can occur within one single day and are externally influenced. The instability of someone with borderline personality disorder is chronic.


With bipolar disorder, individuals often face challenges in relationships but the focus of these is the extremes of moods rather than instability. Borderline personality disorder, on the other hand, has a severe impact on personal relationships. People with BPD often struggle with fear of abandonment, which leads to unstable and intense relationships.


In bipolar disorder, an episode of mania or depression can occur spontaneously or it can be triggered by a life event. However, the episodes aren’t linked to interpersonal stressors exclusively. In borderline personality disorder, mood swings are triggered by perceived abandonment and conflicts.

Mood episodes in Bipolar Disorder

Many individuals who are diagnosed with bipolar disorder were first diagnosed with depression. This is because their initial symptoms might have been depressive ones rather than manic ones. During a period of depression, a person with bipolar disorder will have overwhelming feelings of sadness and worthlessness. This can lead to suicidal ideation. 

During an episode of mania, an individual will feel very happy and euphoric. They will have ambitious ideas and plans with copious amounts of energy. They may also spend money impulsively and substantially, even on things they don’t really want or can’t afford.

People might also not feel like sleeping or eating during mania. They might talk quickly and get annoyed easily. Lots of people also feel really creative. However, there are also possible negative symptoms during mania like psychosis.

Emotional dysregulation in Borderline Personality Disorder

In borderline personality disorder, emotional dysregulation is a key feature. The instability is chronic and manifests in many ways:

  • Intense mood swings that come quickly. These can be extreme lows and highs, often within a very short period like a day.
  • Irritability and anger. Anger is often triggered by perceived abandonment or conflicts. It can be intense and lead to aggression or impulsivity.
  • Fear of abandonment. With BPD, there is a pervasive fear of abandonment. This triggers intense emotions and frantic efforts to avoid being abandoned—even when there is no evidence.
  • Idealisation. Individuals idealise others and see them as perfect. This can often lead to devaluation when they are disappointed, thus straining the relationship.
  • Self-harm and suicidal ideation. Emotional dysregulation can lead to self-harming behaviours. There might be cutting, burning or suicide attempts as a way to cope with the emotional pain.
  • Dissociation. This occurs when individuals feel disconnected from their surroundings, feelings and thoughts. This is a coping mechanism to manage overwhelming emotions.
  • Difficulty expressing emotions. Despite intense emotions, people with BPD often struggle to express their feelings healthily. These can lead to relationship instability.

Diagnosis and assessment

If a GP thinks you may have bipolar disorder or borderline personality disorder, they’ll usually complete a referral to a psychiatrist. Unlike depression and anxiety, GPs aren’t qualified to diagnose BD or BPD and will, therefore, need to refer patients to a specialist. 

When individuals are referred to a psychiatrist, they will undergo a specialist assessment to find out the most likely diagnosis. This will involve lots of questions about symptoms both past and present, including when the condition first started. There might also be tests to check for physical problems that could cause symptoms like an overactive or underactive thyroid. 

During or post-diagnosis, a community mental health team (CMHT) might support individuals.

Treatment Talking Therapy for Bipolar Disorder and Borderline Personality Disorder

Treatment approaches

The treatment options available will depend on the exact diagnosis. The treatments for BD and BPD might be similar in some cases but they are judged on an individual basis. 

Bipolar disorder has a range of treatments. These aim to control the effects of an episode so that the individual’s life isn’t so adversely affected.

Medicines for BD

There are mood stabilisers that can be used to prevent episodes of depression and mania. These are taken on a daily basis; it doesn’t matter which type of episode a person is experiencing. 

There are also specific medicines used to treat the symptoms during a manic or depressive episode, which are different from mood stabilisers. For instance, episodes of depression can last up to a year. They’re longer than manic episodes. During these times, the individual may require specific medications to manage their low mood. Manic episodes usually last a few months and are shorter than the depressive episodes. 

Here are some examples of medication:

  • Lithium (a mood stabiliser): This is a long-term treatment that’s usually prescribed for 6 months or more.
  • Anticonvulsant medicines like valproate, carbamazepine and lamotrigine. These are used to treat episodes of mania and are also mood stabilisers.
  • Antipsychotic medicines like aripiprazole, haloperidol, olanzapine, quetiapine and risperidone. These are also mood stabilisers.

Talking therapy

Talking therapy is often used to help individuals manage their feelings around their condition. They are able to learn how to deal with depression and how to improve relationships.

Changes to lifestyle

For some people, changes to lifestyle can help. This might include doing regular exercise, planning fun activities, improving your diet and ensuring good sleep.

In-patient treatment

Occasionally, those with severe episodes might need to stay in hospital if they’re a danger to themselves or others. This would be under the Mental Health Act. Most people, however, don’t need to go to hospital.

BPD treatments

Like BD, individuals with borderline personality disorder are often treated with medication and psychotherapy. However, unlike bipolar disorder, there is debate about whether medicines are helpful with this condition and no medicine is licensed solely for the treatment of BPD. 

However, if the patient has other conditions like depression and anxiety, they may receive treatments for those. 

Largely, BPD treatment centres around psychotherapy and there are lots of different approaches. These are often coordinated by a community mental health team (CMHT), which is made up of community mental health nurses, counsellors, psychotherapists, social workers, psychologists, psychiatrists and occupational therapists.

For severe cases, patients may be entered into the care programme approach (CPA). This is a way to ensure the right treatment is given. The CPA consists of:

  • An assessment of the individual’s social and health needs.
  • The writing of a care plan to meet the needs of the patient.
  • A care coordinator is appointed to oversee the plan as the first point of contact.
  • Reviews of treatments and the care plan.

Psychotherapy for BPD

There are several approved psychotherapies used to treat borderline personality disorder. These include:

Dialectical behaviour therapy (DBT)

This is specifically designed for individuals with BPD. It is based on two key factors that contribute to BPD: emotional vulnerability and adverse childhood experiences. DBT aims to break the negative cycle of experiencing intense emotions and then the feeling of guilt for having the emotions. 

DBT works on validating emotions and being open to opinions and ideas that aren’t your own. It tends to involve both group and individual sessions on a weekly basis. It has been effective, especially for women who have self-harmed or experienced suicidal ideation.

Mentalisation-based therapy (MBT)

This is based on the idea that those with borderline personality disorder struggle to mentalise—in other words, they struggle to think about thinking and assess their thoughts according to whether they’re realistic and useful. Lots of individuals with BPD have urges to self-harm and don’t question them. MBT aims to add a step before the actualisation of self-harm by teaching people to realise it is not a healthy thought to have and is only there due to being upset. 

Most MBT starts with in-patients and the course will last 18 months. Some people are encouraged to stay as an in-patient for the duration.

Living with Bipolar Disorder or Borderline Personality Disorder

Living with both bipolar disorder and borderline personality disorder comes with its challenges. For those with BD, you also must involve the Driver and Vehicle Licensing Agency (DVLA) since the condition can affect driving. 

For both conditions, one of the most important things is to learn to recognise triggers and warning signs. It won’t necessarily prevent any mood changes, but you will be able to act in time and get help to change treatment, if necessary.

Both conditions are easier to manage by leading a healthy and active lifestyle. A good diet with regular exercise and good sleep can help. 

Even if you feel well, you should never miss any checkups or appointments as these are important to keep you feeling well.

Final thoughts on bipolar disorder and borderline personality disorder

Now we’ve examined both conditions, we can see that the biggest differences between them are:

  • Duration of mood changes: Those with BD experience long periods in one ‘mood’ while those with BPD might experience quick mood changes multiple times a day.
  • Medication options: BD is treated with a range of medications while NICE doesn’t recommend medicine to those with BPD.
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About the author

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Louise Woffindin

Louise is a writer and translator from Sheffield. Before turning to writing, she worked as a secondary school language teacher. Outside of work, she is a keen runner and also enjoys reading and walking her dog Chaos.

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