Confusable diagnoses · PANCE / PANRE

Bipolar I Disorder vs Borderline Personality Disorder

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Bipolar I Disorder and Borderline Personality Disorder are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Bipolar I Disorder vs Borderline Personality Disorder at a glance

  • Bipolar I Disorder: At least one lifetime manic episode; depressive and hypomanic episodes common but not required for diagnosis.
  • Borderline Personality Disorder: Pervasive instability of relationships, self-image, affect, and marked impulsivity beginning in early adulthood.

Try two board-style questions on Bipolar I Disorder vs Borderline Personality Disorder

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Question 1PsychiatryMedium
A 40-year-old male with bipolar I disorder, currently euthymic on lithium (level 0.8 mEq/L), develops new hypertension requiring treatment. His primary care provider is reviewing antihypertensive options. Which of the following antihypertensives is most likely to cause lithium toxicity?
  • AMetoprolol
  • BDoxazosin
  • CHydrochlorothiazide
  • DAmlodipine
Reveal answer & full explanation
Correct answer: C — Hydrochlorothiazide
  • AMetoprolol
  • BDoxazosin
  • CHydrochlorothiazide✓
  • DAmlodipine

Why Hydrochlorothiazide is correct

  • Thiazide diuretics such as hydrochlorothiazide (HCTZ) reduce lithium renal clearance: sodium depletion triggers compensatory lithium reabsorption in the proximal tubule, increasing lithium levels 25-40%
  • This is a significant toxicity risk in a patient with a therapeutic lithium level of 0.8 mEq/L

Why the others are wrong

  • Metoprolol — beta-blockers (metoprolol, atenolol) are safe antihypertensives with lithium and do not significantly affect lithium levels
  • Doxazosin — alpha-blockers are safe antihypertensives with lithium
  • Amlodipine — calcium channel blockers (CCBs) such as amlodipine are safe antihypertensives with lithium

Additional high-yield points

  • NSAIDs also increase lithium levels 25-60% by reducing renal prostaglandin synthesis and lithium clearance
  • ACE inhibitors (ACEi) and angiotensin receptor blockers (ARBs) also reduce lithium clearance and raise lithium levels
  • Loop diuretics (furosemide) have less effect than thiazides on lithium levels
  • If a thiazide is required: reduce lithium dose 25-33% and check levels 5-7 days after starting the diuretic
Question 2PsychiatryMedium
A 28-year-old woman with borderline personality disorder presents after a low-lethality overdose of diphenhydramine taken impulsively after a fight with her boyfriend. She is medically stable. She denies ongoing suicidal ideation. She has had multiple similar episodes. Which of the following is the most appropriate psychiatric management?
  • ALithium for mood stabilization
  • BDialectical behavior therapy (DBT)
  • CSelective serotonin reuptake inhibitor (SSRI) monotherapy
  • DBrief supportive psychotherapy
Reveal answer & full explanation
Correct answer: B — Dialectical behavior therapy (DBT)
  • ALithium for mood stabilization
  • BDialectical behavior therapy (DBT)✓
  • CSelective serotonin reuptake inhibitor (SSRI) monotherapy
  • DBrief supportive psychotherapy

Why Dialectical behavior therapy (DBT) is correct

  • Borderline personality disorder (BPD) with recurrent parasuicidal behavior — DBT (Dialectical Behavior Therapy) is the evidence-based treatment of choice for BPD.
  • DBT specifically reduces self-harm behaviors, hospitalizations, and suicidal ideation in BPD.
  • DBT achieves this through skills training: mindfulness, distress tolerance, emotional regulation, and interpersonal effectiveness.

Why the others are wrong

  • Lithium for mood stabilization — Lithium may help specific symptoms (mood lability, impulsivity) but is an adjunct, not primary treatment for BPD.
  • Selective serotonin reuptake inhibitor (SSRI) monotherapy — Selective serotonin reuptake inhibitors (SSRIs) may help specific symptoms (mood lability, impulsivity) but are adjuncts, not primary treatment for BPD; pharmacotherapy alone is insufficient.
  • Brief supportive psychotherapy — Supportive therapy offers containment but lacks the structured skills modules (mindfulness, distress tolerance, emotion regulation) that give DBT its demonstrated reduction in recurrent self-harm in BPD.
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Side-by-side comparison

FeatureBipolar I DisorderBorderline Personality Disorder
At a glanceAt least one lifetime manic episode; depressive and hypomanic episodes common but not required for diagnosis.Pervasive instability of relationships, self-image, affect, and marked impulsivity beginning in early adulthood.
Classic presentationManic patient with reduced need for sleep (e.g., sleeping 2-3 hours and feeling rested), spending sprees, hypersexuality, and grandiose business plans.; Manic episode: elevated, expansive, or irritable mood >=1 week with increased energy/activity; DIG FAST: Distractibility, Indiscretion (risky behaviors), Grandiosity, Flight of ideas,…>=5 of 9 DSM-5-TR criteria: frantic efforts to avoid real/imagined abandonment; unstable intense relationships alternating idealization and devaluation; identity disturbance; impulsivity in >=2 self-damaging areas; recurrent suicidal behavior/gestures/self-mutilation; affective instability (mood reactivity, intense episodic dysphoria);…
Workup / key labsDSM-5-TR Bipolar I: At least one lifetime manic episode — distinct period (>=7 days, or any duration if hospitalized) of elevated/expansive/irritable mood AND increased goal-directed activity/energy, with >=3 DIG FAST symptoms (>=4 if mood is only irritable), causing marked impairment or psychotic features. The episode is not…DSM-5-TR: A pervasive pattern of instability of interpersonal relationships, self-image, and affects, and marked impulsivity, beginning by early adulthood and present in a variety of contexts, with >=5 of the 9 criteria. Diagnosis is clinical; structured interviews (e.g., SCID-5-PD) can aid assessment. May be diagnosed before age 18 if…
ImagingNeuroimaging not routine; consider MRI if atypical features or first episode after age 50Not routinely indicated
First-line treatmentMood stabilizer — lithium (gold standard, anti-suicide effect), valproate, or lamotrigine (bipolar depression and maintenance); Atypical antipsychotic — quetiapine, olanzapine, risperidone, aripiprazole, lurasidone, cariprazine; Acute mania: lithium OR valproate + atypical antipsychotic; add benzodiazepine for agitation; Bipolar…Evidence-based psychotherapy is primary — dialectical behavior therapy (DBT), mentalization-based therapy (MBT), transference-focused psychotherapy (TFP), schema therapy, good psychiatric management (GPM); DBT is the most studied, with RCT evidence for fewer self-harm episodes, suicide attempts, ED visits, and hospitalizations, and…

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Full outlines

Bipolar I Disorder Borderline Personality Disorder (BPD) All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.