Borderline personality disorder (BPD) and bipolar disorder both involve big mood
changes, so they are often confused. The clearest difference is timing: BPD moods shift
within hours to days, often in response to relationships, while bipolar disorder brings
mood episodes that last days to weeks, including periods of mania or hypomania. Only a licensed professional can tell them apart.
| Borderline personality disorder | Bipolar disorder | |
|---|---|---|
|
What it is |
A personality disorder centered
on difficulty regulating
emotions |
A mood disorder with clear
shifts in mood, energy, activity
and concentration |
|
How long mood
changes last |
A few hours to a few days |
Episodes of days to weeks:
manic episodes in bipolar I last
at least 7 days; depressive
episodes typically at least 2
weeks |
|
Periods of elevated
mood |
No. BPD occurs without the
periods of significantly elevated
mood seen in mania or
hypomania |
Yes. Mania (bipolar I) or the
milder hypomania (bipolar II) |
|
What sets moods off |
Often a reaction to something in
a relationship, such as
perceived rejection |
Episodes are lasting changes in
mood and energy, not quick
reactions to a single event |
|
Sense of self and
relationships |
Unstable self-image and
intense, unstable relationships
are core signs |
Not core signs, though episodes
can strain relationships |
|
Main treatment |
Psychotherapy, especially
dialectical behavior therapy
(DBT) |
Medication such as mood
stabilizers, often with
psychotherapy |
|
Role of medication |
Not a first-line treatment;
sometimes added for specific
symptoms |
A core part of treatment,
usually long term |
In BPD, emotions rise fast and settle within hours or a few days. A disagreement in the morning can bring intense anger or despair that has eased by the evening. This pattern is one of the 9 symptoms of BPD.
In bipolar disorder, mood changes come as episodes. A depressive episode typically lasts at least two weeks, and a manic episode in bipolar I lasts at least seven days. Between episodes, mood can be stable for long periods.
In BPD, sensitivity to rejection and fear of abandonment often drive the emotional swings. The shifts tend to follow events between people, such as a cancelled plan or a delayed reply. Bipolar episodes are longer changes in mood and energy. They affect relationships, but relationships are not usually what starts each mood change.
Getting the diagnosis right matters because the treatments differ.
psychotherapy is the primary treatment. DBT was developed specifically for BPD. Medication isn't a first-line treatment but may be added for specific symptoms. Read about BPD treatment and DBT.
mood stabilizers such as lithium or valproate can help prevent mood episodes or reduce their severity, and psychotherapy adds support and skills. Antidepressants are not used on their own, because they can trigger a manic episode.
Yes. BPD often occurs alongside mood disorders, including bipolar disorder. Because the signs overlap, a careful evaluation looks at how long mood changes last, whether there are periods of elevated mood, and personal and family history. Read how to get diagnosed with BPD. Want to reflect on your own patterns first? Our free BPD traits checklist takes a few minutes and needs no email. It is not a diagnosis.
Yes. Both involve mood changes and impulsive behavior, so they can be confused. A key difference is that BPD symptoms happen without the periods of significantly elevated mood seen in mania or hypomania.
Yes. The two can occur together, which is one reason a thorough evaluation matters. Treatment approaches differ, so the right diagnosis helps people get the right care.
The core feature is difficulty regulating emotions, which affects how people see themselves, how they relate to others and how they act on impulse. Fear of abandonment and intense, unstable relationships are among the most recognized traits.
No. They are separate conditions. Bipolar disorder is a mood disorder, while BPD is a personality disorder that mainly affects emotional regulation, self-image and relationships.
If you’re struggling right now, call or text 988 or see crisis support.
National Institute of Mental Health: Borderline Personality Disorder (revised 2025)
National Institute of Mental Health: Bipolar Disorder
National Institute of Mental Health: Bipolar Disorder topic page
