Bipolar Disorder vs Borderline Personality Disorder

Bipolar disorder and borderline personality disorder (BPD) both involve big emotional swings, so they are often confused. The difference lies mostly in timing and pattern. In bipolar disorder, mood shifts come as episodes that last at least four days for hypomania, a week for mania and two weeks for depression, and they often bring changes in sleep and energy. In BPD, emotions surge and shift within hours, usually set off by events in relationships, against a longer-standing pattern of unstable self-image and fear of abandonment. Some people have both. Getting the picture right matters, because the treatments are different.

Two different kinds of conditions

Bipolar disorder is a mood disorder. Between episodes, many people feel much like themselves. Borderline personality disorder is described as a long-standing pattern in how a person experiences emotions, relationships and their own identity. NIMH describes BPD as involving intense and highly variable moods, impulsive behavior, difficulty with relationships and an unstable sense of self.

The difference matters in daily life, too. Someone in a bipolar episode may feel steadily driven or steadily low regardless of what happens around them, while someone with BPD may move through anger, emptiness and relief within a single afternoon as a relationship situation unfolds. Clinicians pay close attention to those details when they listen to your history.

Neither diagnosis is a judgment about who someone is. People with BPD have often lived through painful experiences, and the condition responds to treatment; many people improve substantially. People with bipolar disorder often stay well for long stretches with ongoing care. Using person-first language, and naming the condition rather than the person, helps keep the focus on what helps.

How long mood shifts last

Timing is the most practical clue. NIMH describes BPD moods as coming in episodes "lasting from a few hours to a few days." A painful text message can bring rage or despair within minutes, which may lift by evening if things are repaired.

In bipolar disorder, the American Psychiatric Association’s summary of the criteria requires at least four days in a row for hypomania and at least a week for mania (or any length if hospital care is needed), and depressive episodes last two weeks or more. During those stretches the change is steady: the high or the low carries on regardless of how the day goes. Our page on hypomania describes what a four-day stretch typically looks like.

What sets the shifts off

In BPD, emotional storms are usually reactive. Perceived rejection, criticism or the threat of being left alone are common sparks, and the feelings are intense and hard to calm. In bipolar disorder, episodes can follow stress, sleep loss or substance use, but they can also arrive without an obvious cause, and once under way they take on a life of their own.

Sleep and energy help separate them. A hypomanic or manic episode usually brings less need for sleep and more energy for days at a time. Emotional distress in BPD can disrupt sleep, but it does not typically produce days of feeling rested on very little sleep with an expansive or elevated mood.

Identity, relationships and anger

A 2019 review of studies comparing bipolar II with BPD found the most useful differences were family history, early life experiences, the course of the illness, how mood states feel, personality style and relationship patterns. Impulsivity and treatment response told them apart less well, since both conditions can involve risky behavior.

In BPD, an unstable sense of self and stormy, intense relationships tend to run through life rather than appearing only during episodes. Anger can be sudden and fierce. In bipolar disorder, irritability tends to rise and fall with episodes. Our page on bipolar disorder and anger looks at that pattern, and cyclothymic disorder covers a milder, longer-lasting mood pattern that is sometimes mistaken for BPD.

Side by side

When both are present

Overlap is common. A 2016 meta-analysis found that 21.6% of people with bipolar disorder also met criteria for BPD, rising to 37.7% among those with bipolar II, and that 18.5% of people with BPD had bipolar disorder. NIMH also notes that people with BPD may have depression, anxiety, PTSD, bipolar disorder or substance use alongside it.

Having both raises the stakes. Research on suicide in bipolar disorder lists co-occurring borderline personality disorder among the factors linked to suicide attempts. If you or someone you love is struggling, call or text 988, or chat at 988lifeline.org; in an emergency, call 911.

Treatment is different

For bipolar disorder, mood-stabilizing medication is a central part of long-term care, usually combined with psychotherapy. For BPD, guidelines put psychotherapy first.

• NICE (CG78) states that drug treatment "should not be used specifically for borderline personality disorder or for the individual symptoms or behaviour associated with the disorder," such as self-harm, marked emotional instability or risk-taking. It adds that medication may be considered for co-occurring conditions, and recommends considering a comprehensive dialectical behavior therapy (DBT) program for women with BPD when reducing recurrent self-harm is a priority.
• The American Psychiatric Association’s 2024 BPD guideline recommends a structured psychotherapy with research support, and suggests that any medication be time-limited, aimed at a specific measurable symptom, and used alongside psychotherapy. In announcing it, APA noted that no evidence was found for any medication treating the core symptoms of BPD.
• NIMH describes DBT as developed specifically for BPD, teaching mindfulness and skills to manage intense emotions and reduce self-destructive behavior, and says the benefits of medication for BPD are unclear.

So a mood stabilizer may be essential for someone with bipolar disorder and BPD, because of the bipolar disorder, while the BPD itself is addressed in therapy. Our page on therapy for bipolar disorder covers the approaches studied in bipolar disorder.

Getting an accurate assessment

A thorough evaluation looks at your mood timeline, relationships, early experiences, family history and how past treatments worked. Input from someone close to you can help, and so can tracking mood daily for a few weeks. At Willow & Stone, Dr. Stacey Forbes, a board-certified psychiatric-mental health nurse practitioner, considers both possibilities at the 90-minute evaluation, and the plan that follows reflects what fits. Read more about bipolar disorder treatment at Willow & Stone or start with the complete bipolar disorder guide.

Common Questions

Sources & Further Reading

• NIMH: Borderline Personality Disorder (revised 2025)
• NICE CG78: Borderline personality disorder, recognition and management (recommendations)
• American Psychiatric Association: Updated Borderline Personality Disorder Guideline (news release, 10 Dec 2024)
• Fornaro M et al. Prevalence and clinical features associated with bipolar disorder and BPD comorbidity. J Affect Disord 2016
• Bayes A, Parker G, Paris J. Differential diagnosis of bipolar II disorder and borderline personality disorder. Curr Psychiatry Rep 2019
• American Psychiatric Association: What Are Bipolar Disorders? (reviewed April 2024)

This article is general education, not a diagnosis or advice for your situation. Do not start, stop, or change a medication without talking to the clinician who prescribes it; stopping a mood stabilizer suddenly can trigger relapse.