There are four recognized types of bipolar disorder: Bipolar I, Bipolar II, Cyclothymic Disorder, and Other Specified Bipolar Disorder. Each involves shifts between emotional highs and lows, but they differ in how intense those shifts are, how long they last, and whether depressive episodes are required for diagnosis.
Bipolar I Disorder
Bipolar I is defined by at least one full manic episode. Mania means a period of abnormally elevated, expansive, or irritable mood lasting at least one week (or any length if hospitalization is needed). During a manic episode, you experience at least three additional symptoms, such as racing thoughts, decreased need for sleep, pressured speech, impulsive behavior, or inflated self-importance. If the elevated mood is primarily irritable rather than euphoric, four additional symptoms are required.
What sets Bipolar I apart from the other types is severity. Manic episodes are disruptive enough to cause serious problems at work, in relationships, or in daily functioning. Some episodes involve psychotic features like delusions or hallucinations. Hospitalization is sometimes necessary to keep the person safe. Most people with Bipolar I also experience major depressive episodes, but depression is not technically required for the diagnosis. The manic episode alone is enough.
Bipolar II Disorder
Bipolar II involves hypomania rather than full mania, paired with at least one major depressive episode. Hypomania shares the same core symptoms as mania (elevated mood, increased energy, reduced sleep, racing thoughts) but is shorter and less severe. A hypomanic episode lasts at least four consecutive days, compared to the one-week minimum for mania.
The critical distinction: hypomania does not cause the kind of severe impairment that mania does. You may feel unusually productive, social, or energized, and people around you might notice a change, but it doesn’t derail your ability to function or land you in a hospital. If psychotic features appear during what seems like hypomania, the episode is reclassified as manic, and the diagnosis shifts to Bipolar I.
Bipolar II is sometimes mischaracterized as a “milder” form of bipolar disorder, but that’s misleading. The depressive episodes in Bipolar II tend to be long and debilitating. Many people with Bipolar II spend more total time in depression than those with Bipolar I, which is why it’s frequently misdiagnosed as major depressive disorder. A person may not recognize hypomania as a problem (it can feel good), so they seek help only during depressive episodes, and the bipolar pattern gets missed.
Cyclothymic Disorder
Cyclothymia is a chronic, fluctuating mood disturbance that stays below the threshold of Bipolar I or II. You experience numerous periods of hypomanic-like symptoms and periods of depressive symptoms, but neither set of symptoms is intense or prolonged enough to meet the criteria for a full hypomanic episode or a major depressive episode.
The pattern has to persist for at least two years in adults (one year in children and adolescents), and the person cannot have been free of symptoms for more than two consecutive months during that time. That near-constant cycling is what makes cyclothymia its own diagnosis rather than just occasional moodiness. The ups and downs are real and persistent enough to cause distress and interfere with daily life, even though they never reach the intensity of a full mood episode. Some people with cyclothymia eventually develop Bipolar I or II, but many do not.
Other Specified Bipolar Disorder
This category exists for people whose symptoms clearly fit the bipolar spectrum but don’t check every box for the three types above. Common examples include hypomanic episodes that last only two or three days instead of the required four, hypomanic symptoms that occur without any history of major depression, or a cyclothymic pattern that hasn’t yet lasted the full two years. A clinician uses this diagnosis when the symptoms cause real distress or functional problems, even though they fall short of the standard criteria on a technicality. There is also an “Unspecified” version used when a clinician doesn’t have enough information yet to pin down the specific pattern.
Specifiers That Cross All Types
Beyond the four types, clinicians use specifiers to describe particular patterns within any bipolar diagnosis. Two of the most common are mixed features and rapid cycling.
Mixed features means you experience symptoms of mania and depression at the same time, or in very rapid sequence. You might feel intensely energized yet hopeless, or agitated and restless while also deeply sad. Mixed episodes are particularly distressing and carry a higher risk of self-harm because the combination of despair and impulsive energy is dangerous.
Rapid cycling means you have four or more distinct mood episodes (any combination of depression, mania, or hypomania) within a single year. This pattern affects a significant minority of people with bipolar disorder and is associated with a more difficult treatment course. Rapid cycling can come and go over the lifespan rather than being a permanent feature.
How Bipolar Disorder Looks Different in Children
Children and adolescents can be diagnosed with any of the types above, but their symptoms often look different from adult presentations. Irritability and rage tend to be more prominent than classic euphoria. Kids may cycle between mood states more frequently, sometimes within the same episode, and they’re more likely to experience manic and depressive symptoms simultaneously. Grandiosity in a child might show up as defying teachers or challenging authority figures rather than making grandiose plans. Increased energy might look like signing up for every extracurricular activity available. Parents and teachers are often better at spotting these changes than the child is at reporting them.
What Drives the Mood Shifts
The biological engine behind bipolar disorder involves disrupted signaling between brain cells. Two key chemical messenger systems play central roles. The first involves serotonin and dopamine, which regulate mood, motivation, and reward. In bipolar disorder, the proteins that transport these chemicals work irregularly, and the raw materials needed to produce them can become depleted through oxidative stress. The result is that the brain’s mood-regulating signals become unreliable.
The second system involves glutamate, the brain’s primary excitatory chemical. Brain imaging studies have found elevated glutamate activity in people during manic episodes compared to matched controls, pointing to excessive stimulation in mood-regulating brain regions. The conversation between neurons and the support cells that surround them (which recycle glutamate for reuse) appears to be disrupted, contributing to the instability that defines the disorder. Inflammation also plays a role: elevated inflammatory markers correlate with more severe depressive symptoms and altered chemical messenger turnover in people with bipolar disorder.