Bipolar I vs Bipolar II: What’s the Difference?

Bipolar I and bipolar II are both lifelong mood disorders with depressive episodes and elevated episodes. The difference is how high the highs go. Bipolar I requires at least one manic episode: a week or more of elevated or irritable mood with greatly increased energy, often causing serious problems or needing hospital care. Bipolar II requires at least one hypomanic episode (four days or more, noticeable but not disabling) plus at least one major depressive episode, and no mania ever. The table below sets the two side by side; after it, we take apart the common belief that bipolar II is the milder illness.

The difference in one sentence

The 2023 VA/DoD bipolar guideline defines the two this way: bipolar I is at least one manic episode, with or without depression; bipolar II is at least one hypomanic episode and at least one major depressive episode, never a manic episode. Everything else follows from that line.

That means a person with bipolar I does not need to have had depression to be diagnosed, although NIMH notes separate depressive episodes usually occur. A person with bipolar II, by contrast, must have had both a hypomanic stretch and a major depression. For a refresher on all the episode types, see our bipolar disorder guide.

Bipolar I vs bipolar II: side-by-side comparison

Treatment entries are guideline listings by class and name only, not a recommendation for any one person. Your prescriber weighs history, side effects, other conditions and preferences.

The myth that bipolar II is "milder"

Because hypomania is defined as less severe than mania, it is easy to assume bipolar II is the lighter diagnosis. That reading confuses the highs with the illness. Three points from the research push back:

1. The lows carry the weight. NIMH notes that many people with bipolar II spend long periods in a persistent, low-grade depressive state. Depression is the part of bipolar disorder that most often costs people work, relationships and health.
2. Suicide risk follows depression. An International Society for Bipolar Disorders task force found that suicide attempts were associated with depressive polarity, younger onset, anxiety and substance use, among other factors (Schaffer et al., 2015). None of those spare bipolar II.
3. It is missed for longer. NIMH says people with bipolar II may seek help only for depression, so the hypomanic side goes unnoticed. Years on antidepressants alone, without the right diagnosis, can mean years of incomplete recovery.

The fair summary is "different, not milder." Bipolar I carries the risks that come with mania (psychosis, hospitalization, dangerous decisions), while bipolar II tends to be dominated by depression and diagnostic delay. Both deserve full, ongoing treatment.

Can bipolar II turn into bipolar I?

The labels describe what has happened so far. If someone diagnosed with bipolar II ever has a full manic episode, the diagnosis becomes bipolar I, because bipolar II by definition means no mania has ever occurred. The sources we rely on do not give a dependable rate for how often this happens, so we won't quote one; what matters practically is that new symptoms are reported and the diagnosis is revisited.

The reverse does not happen. Once a manic episode has occurred, the diagnosis stays bipolar I even through long periods of stability.

How a clinician tells them apart

The distinction rests almost entirely on history, so the evaluation focuses on past elevated periods in concrete terms: How long did it last? Did you sleep? Did you miss work, spend money you didn't have, get into legal trouble? Did anyone take you to a hospital? Were there beliefs others found strange?

• Input from a partner or family member, who may remember a week the person minimizes
• Past records, especially any emergency or hospital visits
• How you responded to antidepressants in the past
• A mood and sleep chart kept over weeks to months

Validated questionnaires can support the conversation but cannot settle the type. Read more in how bipolar disorder is diagnosed.

How treatment differs

Both types are treated with mood-stabilizing medication plus psychotherapy and attention to sleep and routine. The differences are in which options guidelines rank first and how cautiously antidepressants are approached.

• Mania (bipolar I only). CANMAT/ISBD 2018 lists lithium, quetiapine, divalproex, asenapine, aripiprazole, paliperidone, risperidone and cariprazine as first-line single options.
• Bipolar II depression. CANMAT/ISBD 2018 lists quetiapine as the only first-line option. Lumateperone (Caplyta) is FDA-approved for depression in bipolar I or II in adults, and a 2023 evidence update to the CANMAT/ISBD guidelines placed it second-line.
• Antidepressants. An ISBD task force advised that in bipolar I, antidepressants be prescribed only as an add-on to a mood stabilizer, and found switch risk appears greater in bipolar I than bipolar II. NIMH says antidepressants are not used alone in bipolar disorder.
• Maintenance. The bipolar I list is longer (lithium, quetiapine, divalproex, lamotrigine, asenapine, aripiprazole and combinations); for bipolar II, CANMAT/ISBD names quetiapine, lithium and lamotrigine.

Detail on each type is on bipolar I disorder and bipolar II disorder; the medication overview is on bipolar medications explained.

Where cyclothymia and other forms fit

Bipolar I and II are not the only categories. Cyclothymic disorder involves at least two years (one year in young people) of frequent hypomanic and depressive symptoms that never reach a full episode; the Merck Manual describes it as commonly a precursor of bipolar I or II. Read more on cyclothymia.

DSM-5 also has "other specified" bipolar disorder for patterns that almost fit, for example hypomania lasting fewer than four days alongside major depression, plus categories for bipolar symptoms caused by a substance or another medical condition. There is no official "bipolar 3."

At Willow & Stone

Sorting out bipolar I from bipolar II, or either from depression, is a large part of a first psychiatric evaluation. Dr. Stacey Forbes, PMHNP-BC, sees people ages 10 and up in Arlington, Texas and by telehealth in Texas, New Mexico, Florida, Alaska, Arizona, Colorado and Washington. See bipolar disorder treatment at Willow & Stone.

Common Questions

Sources & Further Reading

• VA/DoD Clinical Practice Guideline for the Management of Bipolar Disorder (2023)
• NIMH: Bipolar Disorder (NIH Pub. 25-MH-8088, revised 2025)
• Merikangas et al. Bipolar spectrum prevalence in the NCS-R (Arch Gen Psychiatry 2007)
• Schaffer et al. ISBD Task Force on suicide in bipolar disorder (Aust N Z J Psychiatry 2015)
• Yatham et al. CANMAT and ISBD 2018 guidelines for bipolar disorder (Bipolar Disord 2018)
• Merck Manual Professional: Cyclothymic Disorder (Coryell, 2026)

This article is general education, not a diagnosis or advice for your situation. Do not start, stop, or change a medication without talking to the clinician who prescribes it; stopping a mood stabilizer suddenly can trigger relapse.