Because of the significant overlap in symptoms, there’s long been a debate about distinguishing between bipolar disorder (BD) and borderline personality disorder (BPD).

If the experts can’t even agree, how can you figure out if you have one, the other, or both? Here, we’ll describe both disorders and answer the most frequently asked questions about their differences.

About 2.8% of people in the United States are diagnosed with bipolar disorder, a mental health condition characterized by unusual changes in mood, ability to concentrate, energy levels, and the ability to function in daily activities.

During manic episodes, people with BD may feel euphoric, energized, or irritable. In depressive episodes, they often feel sad, apathetic or detached, or hopeless.

The three types of bipolar disorder

BD is classified into three types:

  • Bipolar I disorder: In this type, manic episodes last at least 7 days, and depressive episodes last at least 2 weeks. You may also experience depressive and manic symptoms at the same time.
  • Bipolar II disorder: This type includes a pattern of depressive and hypomanic (less severe mania) episodes.
  • Cyclothymic disorder: In this type, you have depressive and hypomanic symptoms that don’t meet the criteria of either hypomania or major depressive episodes

BD is usually diagnosed in the late teens or early adulthood and can be triggered by stressful events. Treatment includes medication and talk therapy. Common symptoms of BD include:

  • sleep disturbance
  • manic and depressive states
  • stable mood between manic and depressive episodes
  • sustained mood shifts that last days or weeks
  • anger
  • suicidal thoughts or behavior
  • harmful behaviors
  • impulsivity
  • delusions

Borderline personality disorder is a mental health condition that affects a person’s emotional regulation, which can lead to impulsivity, changes in self-esteem, and difficult relationships with other people.

BPD affects 1.4% of the U.S. population; 75% of people with BPD are women.

Symptoms include:

  • intense mood changes
  • uncertainty about sense of self
  • feelings about people change rapidly
  • unstable relationships
  • black-and-white thinking
  • impulsivity (spending sprees, sex without a barrier method, substance use, reckless driving, binge eating)
  • recklessness
  • avoiding abandonment
  • self-harm
  • thoughts of suicide
  • chronic feeling of emptiness
  • difficulty controlling anger
  • dissociation

It’s often treated with individual psychotherapy and family therapy, and sometimes medication.

How can you tell the difference between BD and BPD? Well, it’s not easy.

The key may be to examine what your symptoms are at a single point in time compared to over the history of a longer period, wrote Dr. Ken Duckworth in a 2017 article for the National Alliance on Mental Illness. He also makes these distinctions:

  • Mania with hallucinations is not generally seen in BPD. Psychosis is more common in BD.
  • It’s easier to confuse BPD with bipolar II disorder because manic symptoms are less intense.
  • Insomnia is more likely in BD. People with BPD also experience sleep disturbances but are more likely to have chronic nightmares.
  • Experiencing more intense relationships and conflict may point to BPD.
  • People with BPD are more likely to engage in self-harm that is not suicidal.

One study from 2019 found that three symptoms were useful in distinguishing between patients with BD and BPD: history of elevated mood, history of increased goal-directed activity, and episodic co-occurrence of manic symptoms.

Another more recent study compared MRI data for people with BD and BPD and found that both showed structural differences in the brain.

With both disorders, participants had lower hippocampal volume. People with BPD had smaller amygdalas, and people with BD showed loss of gray matter in the cerebellum, thalamus, parietal, and occipital parts of the brain.

Researchers have found that people with BPD or BD may share some common experiences in their backgrounds, including childhood trauma, a family history of mental health conditions, and experience with substance use disorder.

Symptoms that overlap in the diagnosis of BPD and BP include:

  • mood changes
  • anger
  • suicidality
  • harmful behavior
  • impulsivity
  • delusions

People with BPD or BD may also experience irritability, difficulty concentrating, and rapid switching between thoughts or ideas.

Yes, the two disorders have many symptoms in common.

In fact, some experts think BPD may be part of a bipolar spectrum. It can be particularly hard to distinguish between bipolar disorder and cyclothymic disorder because in both cases, patients have rapidly changing moods.

The severity and history of symptoms at the time of diagnosis can also have a big impact on which label you’re given. Because different treatments are more effective for different mental health conditions, it’s important to get the most accurate diagnosis from the start.

While people with bipolar disorder usually experience distinct periods (lasting days or weeks) of high and low moods over time, people with BPD often have rapidly changing moods.

BPD mood changes may be more brief, but they can also be very intense. They make a person’s mood more unstable. Mood changes in people with BPD also seem to be more often triggered by outside factors like stress at work or in relationships.

Yes, people are often diagnosed with both BD and BPD.

According to a 2019 review of studies, among people with BPD, 2.2% to 16.1% also had bipolar disorder I, and 4.8% to 18.7% also had bipolar disorder II. Another study in the review found that 21% of people with bipolar disorder also had BPD, with a higher prevalence among younger women.

Mental health conditions aren’t ranked according to which one is “better” or “worse.” Every person’s experience with a mental health condition is individual and changes over time.

Some factors that can make the experience of BPD and BD different include:

  • Bipolar disorder is a lifelong condition that will always require management. In contrast, borderline personality can be treated to the point that it no longer needs long-term management.
  • The intensity of symptoms can vary widely in both disorders, but the intensity of BPD symptoms can be more pervasive and potentially last longer than BD symptoms.
  • Both diagnoses are associated with suicidal behavior, but people with BPD will often engage in self-harm without suicidal intentions.

Ultimately which disorder is “worse” will depend on the person, the day, and how effective the treatment is.

Bipolar disorder and borderline personality disorder can be difficult to distinguish because of overlapping symptoms, common family histories, and association with traumatic experiences. It’s possible to be diagnosed with both disorders, and some experts think they may be on the same spectrum.

It’s important to report your history and how symptoms have changed to get the most accurate diagnosis because your doctor may recommend different types of therapy or medication for one versus the other.