BPD vs Bipolar: Why They Are Often Confused

Parents often become concerned when they see sudden or dramatic changes in a teen’s behavior — intense moodiness, impulsive choices, emotional outbursts, or periods of withdrawal that don’t feel like typical adolescent ups and downs. But it can be hard to know what’s driving the behavior or what kind of help they need. Bipolar disorder and borderline personality disorder (BPD) are two conditions that may come up in this search for answers because both can involve strong emotions and unpredictable mood swings.

But the two disorders are very different. Bipolar disorder is a mood disorder, meaning it involves shifts in mood, energy, and behavior that unfold in distinct episodes. BPD is a personality disorder, which refers to a longer-term pattern of emotional and interpersonal volatility. Understanding the difference is important because for kids with these disorders to thrive they need very different kinds of treatment.

“It’s easy to mistake one kind of emotional intensity for another,” says Blaise Aguirre, MD, a child and adolescent psychiatrist and founding medical director of 3East, the dialectical behavior therapy (DBT) unit at McLean Hospital in Boston. “But understanding what drives those emotions is the key to getting teens the right treatment.”

According to Dr. Aguirre, several factors contribute to the confusion between BPD and bipolar:

• The term “mood swings” can be misinterpreted: Asking whether a teen has “mood swings” doesn’t distinguish between the weeks- or months-long episodes of mania or depression in bipolar disorder and the rapid, reactive shifts of BPD. “People say, ‘Do you have mood swings?’” Dr. Aguirre notes, “and when a teen says yes, the leap is often to bipolar disorder.”
• The two disorders share the same acronym: “BPD” can refer to bipolar disorder or borderline personality disorder, which can cause confusion — especially online.
• Public awareness is uneven: Bipolar disorder is widely described in the media and in popular culture, as well as in advertising for medication. “Big Pharma promotes mood stabilizers,” Dr. Aguirre says, “but no one is promoting dialectical behavior therapy,” which is the most effective treatment for BPD.
• Both conditions involve emotional instability: Extreme emotions are characteristic of both disorders, but “in BPD, episodes of dysregulation last minutes or hours,” Dr. Aguirre says. “In bipolar disorder, episodes last weeks or longer.” Episodes in bipolar disorder often arise without an external trigger. In BPD, emotional storms are almost always triggered by something outside the teen — an argument, or an unexpected change in plans — or something inside the teen, like a self-critical thought or perceived rejection.
• Social media adds another layer of confusion: Teens are often exposed to descriptions of BPD and bipolar disorder on TikTok or Instagram before receiving reliable clinical information. “It can be empowering,” Dr. Aguirre says, “but it can also spread misinformation.”

Bipolar disorder is a biologically based mood disorder marked by alternating periods of depression and mania or hypomania. These shifts involve changes in sleep, energy, and behavior that are difficult for teens to control.

• Elevated or irritable mood
• Increased energy
• Decreased need for sleep
• Racing thoughts
• Rapid or pressured speech
• Risk-taking behavior

• Persistent sadness or hopelessness
• Low energy
• Sleep or appetite changes
• Loss of interest in activities
• Difficulty concentrating

What distinguishes bipolar disorder is its episodic nature. Teens often return to a more stable baseline between episodes. Dr. Aguirre says the condition typically emerges later in adolescence than borderline personality disorder. “I tend to see the first break episode in later adolescence or early adulthood,” he says. And while stress can play a role, “there tends to be more of a genetic load” in bipolar disorder compared to BPD.

Borderline personality disorder is a condition in which overwhelming emotions create instability in a person’s relationships and sense of self. Teens with BPD often feel emotions intensely and struggle to return to baseline once they’re upset. It can lead to profoundly negative feelings, including self-hatred and suicidality.

• Intense, rapidly shifting moods
• Fear of abandonment
• Unstable or chaotic relationships
• Impulsivity, including self-harm
• Chronic emptiness
• Difficulty with identity or self-image

It’s common for teenagers with BPD to have experienced trauma or neglect, although it can also develop when a very sensitive child finds ordinary parenting invalidating. “You’re more likely to find early childhood trauma or invalidation in people with BPD,” he says. “In bipolar disorder, you’re less likely to see that history.” Unlike bipolar disorder, BPD symptoms don’t appear in episodes. They are part of a long-standing emotional, interpersonal, and behavioral pattern.

Highly sensitive temperament is central to BPD. “I’ve never met a person with borderline personality disorder who isn’t a highly sensitive person,” Dr. Aguirre says. Sensitive people react strongly to emotional experiences and once they are upset they take longer to recover. Many grow up in environments where their sensitivity was misunderstood or dismissed, leading to a sense of invalidation.

Parents often notice that their child reacts to things with more intensity than siblings or peers do. It is also something many parents recall from early childhood. “Parents often tell me their children were sensitive straight out of the womb,” Dr. Aguirre says.

Borderline personality disorder often emerges soon after puberty, when emotional intensity and social pressures increase. “Something happens around puberty,” Dr. Aguirre says. “You start to see impulsive and dangerous behaviors — fast driving, spending money, sexual encounters — behaviors younger children wouldn’t exhibit.”

Bipolar disorder tends to develop later — in the late teens or young adulthood. Early signs such as irritability, inconsistent sleep, or unusual energy may eventually develop into longer, more clearly defined episodes.

A younger teen whose emotions shift quickly in response to conflict is more likely showing traits of BPD. An older teen with prolonged periods of elevated or depressed mood, especially with disrupted sleep or energy, may be developing bipolar disorder.

Both disorders can involve impulsive or risky behavior, which is why parents often struggle to tell them apart. But the motivations behind the behavior are different. “Often these symptoms in BPD are used to regulate how they feel,” Dr. Aguirre says. “A teen might think, ‘I don’t feel attractive or lovable, so I’ll sleep around to change how I feel.’” In mania, however, risk-taking stems from elevated mood and grandiosity. “It’s not to change anything,” he says. “It’s because they already feel great.” Understanding the purpose behind a behavior helps clinicians distinguish the two disorders.

Misdiagnosis is common, particularly when teens with BPD are labeled as having bipolar disorder. “They come to us on a lot of medications,” Dr. Aguirre says. “They’ll say, ‘These medications aren’t helping me.’ And they often feel worse because the side effects, like weight gain, add to their unstable sense of self.”

When teens learn about DBT, many of them look up what DBT is and see that it is a treatment for BPD. “Then they look up borderline personality disorder and say, ‘This actually makes more sense than bipolar to me,’” he says. The reverse misdiagnosis is rare. “Maybe once a year I see that.”

Sometimes, the disorders occur together. “You can certainly have comorbidity,” Dr. Aguirre says. And co-occurring conditions such as anxiety, ADHD, PTSD, depression, and trauma histories can complicate the picture and the diagnosis because they all shape how symptoms appear. Dr. Aguirre worries about teens being diagnosed too quickly. Many who say they are “depressed” may actually be overwhelmed by existential worry — about world events, climate change, or the future. Accurate diagnosis requires understanding how each symptom works in a teen’s life rather than treating them as interchangeable.

Both BPD and bipolar disorder carry elevated suicide risk, but the patterns are different. “In BPD, suicidality can feel like it’s always hovering in the background,” Dr. Aguirre says. “In bipolar disorder, it tends to surge during depressive episodes. The key is understanding the pattern so you can put the right supports in place.”

Bipolar disorder is usually treated with a combination of therapy and medication. Therapy, such as cognitive behavioral therapy (CBT) or family-focused therapies for bipolar, helps teens learn to recognize early warning signs and maintain routines that support stability. Medication (mood stabilizers or atypical antipsychotics) help manage episodes.

For BPD, the most effective treatment is dialectical behavior therapy (DBT), which teaches skills in:

• Emotion regulation
• Distress tolerance
• Mindfulness
• Interpersonal effectiveness

Medication may help with co-occurring conditions but is not the primary treatment for BPD. With the right support, teens with BPD often make significant progress and go on to build healthy, stable lives.

When a teen says something like “I’m terrible” or “Nobody likes me,” a parent’s instinct is to reassure them. But reassurance alone rarely helps. Dr. Aguirre encourages parents to stay curious. “Rather than saying, ‘That’s not true,’ ask where the thought came from,” he says. “Explore what happened. Try to understand the story behind the emotion.” Teens who feel heard — rather than corrected — are more willing to open up and accept support.

Parents can also pay attention to patterns. A teen whose emotions rise and fall quickly, usually in response to conflict, may be showing signs of BPD. A teen with prolonged periods of elevated or depressed mood, especially with changes in sleep or energy, may be struggling with bipolar disorder. Early, compassionate support can make a meaningful difference no matter the diagnosis.