These two mental illnesses are often mistaken for each other but are quite different, despite each being marked by unstable moods. Bipolar Disorder (BD) is a mood disorder, whereas Borderline Personality Disorder (BPD) is one of the personality disorders. In this insight, I explain how they are distinct conditions with different causes, symptoms, and treatments.
What Is Bipolar Disorder?
As a mood disorder, bipolar disorder in young adults is marked by significant shifts in mood, energy, activity levels, and concentration and which are not specifically triggered by events. Moods alternate between depressive episodes and hypomanic or manic episodes lasting days to weeks or more.
Hypomanic episodes are of less intensity and duration than manic episodes. Both involve elevated mood (feeling “high”) and the following symptoms [1]:
- Intense feelings of happiness
- Irritability
- Grandiose sense of ability, knowledge, or power
- Decreased need for sleep
- Talking fast with racing thoughts
- Poor judgement with risky behavior such as excessive spending or hypersexuality
Depressive episodes involve prolonged feelings of:
- Sadness
- Fatigue
- Low energy with no interest in usual activities
- Hopelessness
- Sleeping too much
- Possible suicidal thoughts
- Feeling lonely or isolating from others
- Eating more or less than usual
There is a strong genetic component to the causes of bipolar disorder. The onset is typically in late teens to 30s, often triggered by stress or substance use.
There is also a biological/circadian rhythm component to bipolar disorder.
Dopamine dysregulation: This involves neurotransmitter dysregulation as abnormalities in dopamine, serotonin, and norepinephrine systems appear to play a role.This is particularly tied to manic and depressive episodes—high activity may trigger mania, low activity depression.
Circadian Rhythm and Sleep Regulation: Many with bipolar disorder have abnormalities in their biological clock (suprachiasmatic nucleus) and melatonin regulation. Disruptions in sleep-wake cycles can trigger mood episodes.
Types of Bipolar Disorder
Bipolar and related disorders are of several types [B]:
Bipolar I disorder
- At least one manic episode before or after hypomanic or major depressive episodes.
- Mania may cause a break from reality, called psychosis.
Bipolar II disorder
- At least one major depressive episode and at least one hypomanic episode.
- No manic episodes.
Cyclothymia
- At least two years in young adults or adults with many periods of hypomania symptoms and periods of depressive symptoms.
- Symptoms are less severe than major depression.
Other types
- Bipolar and related disorders caused by certain drugs or alcohol, or due to some medical conditions, such as multiple sclerosis or stroke.
What is Borderline Personality Disorder (BPD)?
BPD is the most common personality disorder in young people. It is primarily marked by intense fears of abandonment and rejection. Most often this stems from attachment distress in childhood due to abuse or neglect, whether emotional or physical, and emotional invalidation. There is also an element of genetic predisposition. Symptoms typically emerge in the teens/early 20s.
There are many characteristics of BPD, including [3]:
- Emotional dysregulation: Moods shift rapidly and with intensity (often within hours). Often triggered by fear of abandonment, rejection, and other forms of interpersonal distress, leading to unstable relationships.
- Unstable Self-Image: Sense of self fluctuates with difficulty establishing a stable identity.
- Impulsive and Self-Destructive Behaviors: Involved with risky behaviors like substance abuse, reckless spending, or self-harm, often in response to emotional pain.
- Unstable Relationships: Characterized by intense idealization alternating with devaluation, often referred to as “splitting”.
- Chronic Feelings of Emptiness: Feelings of emptiness and loneliness persist, even when with others.
- Difficulty Managing Anger: Outbursts of anger, irritability, and difficulty controlling these feelings.
- Temporary Paranoid Thoughts or Dissociation: Under stress, has brief periods of paranoia or detachment from reality.
- Suicidal Thoughts or Behaviors: Repeated suicidal thoughts, gestures, or attempts.
Bipolar Disorder Compared With Borderline Personality Disorder
Professional clinical assessments for both of these disorders are required, rather than self-diagnosis. The following table compares differences in the key features of each condition:
| Feature | Borderline Personality Disorder | Bipolar Disorder |
| Duration | Minutes to Hours | Days to weeks/months |
| Trigger | Interpersonal Stress | No clear trigger (genetic) |
| Baseline | Chronically unstable | Returns to stable mood |
| Self-Harm & Suicide Risk | Self-harm (cutting, burning) is common. Suicide attempts may be impulsive but less lethal. Constant emotional turbulence | Suicide attempts more likely in depressive or mixed episodes and are more lethal. Mood returns to baseline |
Can You Have Borderline Personality Disorder And Bipolar Disorder?
Research shows that borderline personality disorder is a common personality disorder that co-occurs with bipolar disorder. Both disorders share many common characteristics. The central overlapping feature is mood instability. About 20% of bipolar II patients and 10% of bipolar I patients have comorbid BPD, and there is a strong relationship between BPD and bipolar disorder II [4].
The quality of life and health outcomes in bipolar patients are negatively affected in those who also have BPD, including:
- Higher likelihood of hospitalization
- Longer treatment duration
- Worse response to treatment
Bipolar patients with BPD also have:
- A higher treatment drop-out rate
- Increased risk of substance abuse
- Greater impairment of social and occupational functioning
As bipolar disorder and BPD are each risk factors for suicidal behavior, patients with co-occurring bipolar disorder and BPD also have a higher suicide risk.
Treatment Options for Bipolar Disorder and BPD
When comparing BPD with BD, a simple way to think of it is:
- If mood shifts are rapid, reactive to relationships, and accompanied by fear of abandonment, then a young adult may have BPD.
- If mood shifts are prolonged, cyclical, with periods of high energy/impulsivity, then a young adult may have Bipolar Disorder.
Misdiagnosis is common—proper evaluation by a mental health professional is crucial. Both conditions are treatable, but early intervention improves outcomes.
Recommended treatment of each condition is as follows:
| Bipolar Disorder | Borderline Personality Disorder | |
| Medication | Mood stabilizers (e.g., lithium), antipsychotics, sometimes antidepressants. | No specific drug for BPD, but antidepressants or mood stabilizers may help symptoms. |
| Therapy | Cognitive Behavioral Therapy (CBT). Psychoeducation for mood management. | Dialectical Behavior Therapy (DBT) is the gold standard—focuses on emotional regulation, distress tolerance. |
- Cognitive Behavioral Therapy (CBT): For bipolar disorder, it addresses negative thought patterns, improves emotional regulation, and prevents relapse. Identifies triggers, develops coping strategies, and stabilizes mood swings. Combined with medication, CBT enhances functioning and reduces severity of symptoms, promoting long-term stability.
- Dialectical Behavior Therapy (DBT): A type of CBT. Focuses on emotional regulation, tolerance of distress, mindfulness, and effectiveness of interpersonal relations. Originally developed for borderline personality disorder, DBT also helps bipolar patients manage intense mood swings, reduce self-harm, and improve relationships. Combines individual therapy with skills training for better emotional control.
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Sources
[1] National Institute of Mental Health. Bipolar Disorder in Teens and Young Adults: Know the Signs
[2] Mayo Clinic. 2024. Bipolar disorder.
[3] Cheo. Borderline Personality Traits In Youth.
[4] Patel, R..et al. (2019). Bipolar Disorder and Comorbid Borderline Personality Disorder: Patient Characteristics and Outcomes in US Hospitals. Medicina (Kaunas, Lithuania), 55(1), 13.