BPD stands for borderline personality disorder, not bipolar disorder. Bipolar disorder is typically abbreviated as BD or BP in medical literature. The confusion is understandable because the two conditions share overlapping symptoms like mood instability, impulsivity, and emotional intensity, and roughly one in five people with either diagnosis also meets criteria for the other. But they are fundamentally different conditions with different causes, different patterns, and different treatments.
Why the Two Get Confused
Both borderline personality disorder and bipolar disorder involve dramatic shifts in mood and behavior, which is why they’re frequently mixed up, sometimes even by clinicians. Overlapping symptoms include impulsivity, mood instability, inappropriate anger, and suicidal thoughts. The American Journal of Psychiatry has noted that BPD is commonly misdiagnosed as bipolar disorder because of this symptom overlap.
The confusion runs in both directions. About 21.6% of people with bipolar disorder also have borderline personality disorder, and about 18.5% of people with BPD also have bipolar disorder. That high rate of overlap, roughly one in five for each group, makes the diagnostic picture even murkier. Comorbidity is especially common in bipolar II, where nearly 38% of patients also meet criteria for BPD.
How Mood Shifts Differ
The clearest difference between the two conditions is how long mood episodes last and what sets them off.
In BPD, mood shifts happen within a single day or even hour to hour. Everything can feel fine in the morning and awful by the afternoon. These shifts are almost always triggered by something interpersonal: a perceived slight, a fear of being abandoned, a conflict with someone close. Small stressors can set off intense emotional reactions that feel wildly out of proportion to the situation.
In bipolar disorder, mood episodes last days, weeks, or even months. A manic episode involves a sustained period of elevated energy, reduced need for sleep, and often grandiose thinking. A depressive episode is a prolonged stretch of low mood and withdrawal. Critically, these episodes are not driven by interpersonal conflict. They tend to arise on their own, following an internal biological rhythm rather than reacting to external events.
Core Symptoms of Each Condition
Borderline personality disorder is classified as a Cluster B personality disorder, a group of conditions characterized by unstable moods, impulsive behavior, and difficulty functioning in relationships. People with BPD often experience intense fears of abandonment, a tendency to see others as either entirely good or entirely bad, a poor or unstable sense of self, self-harming behaviors, and chronic difficulty managing unpleasant emotions. Relationships tend to be chaotic because everyday disagreements can trigger overwhelming emotional responses.
Bipolar disorder is a mood disorder, not a personality disorder. It centers on distinct episodes of mania (or hypomania, a milder form) alternating with depression. During manic episodes, people often sleep far less than usual without feeling tired, take on risky projects, spend impulsively, or feel an inflated sense of their own abilities. Between episodes, many people with bipolar disorder return to a relatively stable baseline, something that is less typical in untreated BPD, where emotional instability tends to be more constant.
Treatment Looks Very Different
This distinction matters most when it comes to treatment, because the two conditions respond to entirely different approaches.
For BPD, psychotherapy is the primary treatment. Dialectical behavior therapy (DBT), a structured form of therapy that teaches emotional regulation, distress tolerance, and interpersonal skills, is considered the gold standard. No medications are approved specifically for BPD. Drugs are sometimes prescribed to manage particular symptoms like impulsivity or mood swings, but clinical guidelines treat them as secondary to therapy, not as a standalone solution. One small controlled study found no significant benefit from adding an antidepressant to DBT for BPD patients.
For bipolar disorder, medication is the foundation. Mood stabilizers are considered among the most effective treatments, with well-documented benefits for preventing both manic and depressive episodes and reducing suicide risk. Therapy can be a useful addition, but managing bipolar disorder without medication is rarely recommended.
Getting the diagnosis right has real consequences. Someone with BPD who is treated only with mood stabilizers and never offered therapy is unlikely to see meaningful improvement in their relationships or emotional patterns. Someone with bipolar disorder who is directed toward therapy alone without mood-stabilizing medication risks uncontrolled manic or depressive episodes.
Can You Have Both?
Yes, and it’s not rare. A large meta-analysis found that about 10% of people with BPD have bipolar I and another 10% have bipolar II. When both conditions are present, treatment typically needs to address each one: medication for bipolar cycling and structured therapy for the personality-driven patterns of BPD. If you’ve been diagnosed with one and feel the diagnosis doesn’t fully explain your experience, it’s worth raising the question of whether the other condition might also be present.