ICD-11 describes bipolar type I disorder as characterized by recurrent or at least one manic or mixed episode and, in most cases, also depressive episodes. The text specifies that a manic or mixed episode is required for diagnosis, whereas depressive episodes may occur during the course of the disorder but are not mandatory.

The NIMH brochure explains: “People with bipolar disorder experience periods of unusually intense emotion, changes in sleep patterns and activity levels, and uncharacteristic behaviors, often without recognizing their likely harmful or undesirable effects.” It notes that “these distinct periods are called ‘mood episodes.’ Mood episodes are drastically different from the moods and behaviors that are typical for the person.” It specifies that bipolar I disorder is “defined by manic episodes that last at least 7 days… usually, depressive episodes occur as well, typically lasting at least 2 weeks,” and that bipolar II disorder is “defined by a pattern of depressive and hypomanic episodes.” This directly links bipolar disorder to manic or hypomanic episodes and depressive episodes.

WHO states: "Bipolar disorder is a mental health condition that affects a person’s mood, energy, activity and thought and is characterized by manic (or hypomanic) and depressive episodes." It further explains that during a manic episode a person has an extremely high mood and energy, whereas during a depressive episode a person experiences depressed mood and loss of interest or pleasure.

The authors explain: "To diagnose bipolar I disorder the presence of at least one past or present manic or mixed episode is mandatory. Depressive episodes may occur, but are not obligatory." They contrast this with bipolar II: "to diagnose bipolar II disorder, the presence of at least one hypomanic and one depressive episode in the course of the illness is required." They further note that a past manic episode requires a bipolar I diagnosis even if only the manic pole is seen clinically at that time.

In discussing diagnostic criteria, NIMH notes that “mania is a symptom of bipolar disorder. According to the Diagnostic and Statistical Manual for Mental Disorders (DSM-IV), it is generally defined as a discrete period of increased energy, activity, euphoria or irritability that leads to marked impairment in one’s daily life.” It contrasts this with hypomania, “a milder form of mania,” and explains that the majority of people diagnosed with bipolar disorder experience repeated episodes of hypomania rather than full mania. This underscores that manic or hypomanic episodes are core to bipolar disorder, in addition to depressive episodes discussed elsewhere in NIMH materials.

Reviewing ICD-11, the paper notes that bipolar disorders are subdivided into bipolar I and bipolar II, with criteria analogous to DSM-5. It summarizes that bipolar I requires at least one manic or mixed episode, while depressive episodes are common but not required, and bipolar II requires at least one hypomanic episode and one major depressive episode, without any history of mania.

The Merck Manual explains: "Bipolar disorders are characterized by alternating episodes of mania or hypomania and depression." It continues, "Diagnosis of bipolar I disorder requires at least one episode of mania; major depressive episodes are common but are not required for the diagnosis." For bipolar II, it states, "Diagnosis of bipolar II disorder requires meeting the DSM-5-TR criteria for at least 1 hypomanic episode as well as at least 1 major depressive episode." These descriptions explicitly tie bipolar disorders to episodes of mania or hypomania and episodes of depression, with some variation between bipolar I and II.

AAFP explains that bipolar I disorder is defined by at least one manic episode and that "the manic episode may have been preceded by and may be followed by hypomanic or major depressive episodes." It notes that bipolar II disorder involves "at least one hypomanic episode and at least one major depressive episode" without any history of a full manic episode.

The APA article describes bipolar spectrum disorders as involving mood episodes that can be manic, hypomanic, depressive, or mixed. It notes that episodes may include both manic and depressive symptoms ("mixed mania" or "mixed hypomania") and discusses the importance of identifying these episodes across the spectrum of bipolar disorders.

The document defines: "Bipolar disorders is a category of mood disorders defined by the occurrence of one or more episodes of abnormally elevated mood, clinically referred to as mania or, if mood elevations are milder, hypomania." It adds: "Individuals who experience manic episodes also commonly experience depressive episodes or symptoms, or mixed episodes in which features of both mania and depression are present at the same time. The disorders are subdivided into bipolar I, bipolar II, and other types, based on the nature and severity of mood episodes experienced."

Under "For a diagnosis of bipolar I disorder, it is necessary to meet the following criteria for a manic episode. The manic episode may have been preceded by and may be followed by hypomanic or major depressive episodes." For bipolar II disorder: "For a diagnosis of bipolar II disorder, it is necessary to meet the following criteria for a current or past hypomanic episode and the criteria for a current or past major depressive episode." The same document defines major depressive episode criteria separately, including at least 5 symptoms over a 2‑week period with depressed mood or loss of interest as a core feature.

The UK National Health Service explains: “Bipolar disorder is a mental health condition that affects your moods, which can swing from 1 extreme to another. It used to be known as manic depression.” It says that people with bipolar disorder have “episodes of depression (feeling very low and lethargic) and mania (feeling very high and overactive).” It also mentions hypomania as a milder form of mania that some people experience. This indicates that bipolar disorder is characterized by both depressive and manic/hypomanic episodes.

Discussing ICD-11, the article notes that the classification has adopted subtypes of bipolar disorder, specifically bipolar I and II, based on partitioning mania into mania and hypomania. It emphasizes that within ICD-11, the only criteria distinguishing hypomania from mania are duration and severity. It also points out that presentations of mania without any depressive episodes (unipolar mania) are not given a separate diagnosis and are automatically subsumed under bipolar disorder in ICD-11.

NIMH describes bipolar disorder as "a mental illness that causes unusual shifts in a person's mood, energy, activity levels, and concentration" with mood episodes that range from extremely "up," elated, irritable, or energized behavior (manic or hypomanic episodes) to very "down," sad, indifferent, or hopeless periods (depressive episodes). It specifies that bipolar I disorder is defined by at least one manic episode that may be preceded or followed by hypomanic or major depressive episodes, while bipolar II disorder is defined by a pattern of depressive episodes and hypomanic episodes, but not full-blown manic episodes.

Harvard Health notes that bipolar disorder "is a mental health disorder often characterized by wide mood swings from high (manic) to low (depressed)." It explains that bipolar I is the classic form where a person has had at least one manic episode, and that in bipolar II "the person has never had a manic episode, but has had at least one hypomanic episode and at least one period of significant depression." It adds that most people who have manic episodes also experience periods of depression.

The slides state: "It is necessary to meet criteria for a manic episode to make a diagnosis of bipolar I disorder, but it is not required to have hypomanic or major depressive episodes." Elsewhere it notes that bipolar II disorder "requires at least one hypomanic episode and one major depressive episode." The material emphasizes that bipolar I is defined by manic episodes, whereas bipolar II is defined by both hypomanic and major depressive episodes.

This overview, adapted from NIMH, states that bipolar disorder “is a mental illness that causes unusual shifts in a person’s mood, energy, activity levels, and concentration.” It notes that these moods “range from periods of extremely ‘up,’ elated, irritable, or energized behavior (known as manic episodes) to very ‘down,’ sad, indifferent, or hopeless periods (known as depressive episodes). Less severe manic periods are known as hypomanic episodes.” This reinforces that bipolar disorder involves manic or hypomanic episodes and depressive episodes.

Citing NIMH, the fact sheet states: “People with bipolar disorder experience unusually intense emotional states that occur in distinct periods called ‘mood episodes.’ Each mood episode represents a drastic change from a person’s usual mood and behavior.” It explains that “an overly joyful or overexcited state is called a manic episode, and an extremely sad or hopeless state is called a depressive episode. Sometimes, a mood episode includes symptoms of both mania and depression. This is called a mixed state.” It also adds that bipolar disorder can involve hypomania, “a less severe form of mania.”

The Royal College of Psychiatrists explains that bipolar disorder (formerly manic depression) is an illness in which "you have changes in mood that swing from high (mania or hypomania) to low (depression)." It notes that these mood swings can be extreme and that many people with bipolar disorder have episodes of both depression and mania or hypomania.

CAMH describes bipolar disorder as “a mental illness that affects the way people feel, think and act. It is marked by extreme mood changes – from extreme highs (mania or hypomania) to extreme lows (depression).” It notes that “these mood changes are called episodes” and that people may have periods of normal mood between episodes. This presentation clearly identifies episodes of mania or hypomania and episodes of depression as defining features of bipolar disorder.

MedlinePlus explains: "Bipolar disorder is a mental disorder that causes extreme changes in mood, energy, and activity levels. These moods range from periods of extremely ‘up,’ elated, and energized behavior, known as manic episodes, to very sad, ‘down,’ or hopeless periods, known as depressive episodes." It also notes that some people have hypomanic episodes, which are similar to manic episodes but less severe.

This educational handout explains that “bipolar disorder is an illness that causes mood swings that are more extreme than normal ups and downs. People with bipolar disorder have episodes of depression and episodes of mania.” It adds that “some people have hypomanic episodes, which are like manic episodes, but less severe and troublesome.” This description links bipolar disorder specifically to episodes of depression, mania, or hypomania.

Summarizing ICD-11, the page states that bipolar type I disorder requires "at least one manic or mixed episode" to have occurred. It notes that symptoms must include an altered mood state consistent with a manic and/or depressive episode, but that depressive episodes are not necessary for the diagnosis as long as a manic or mixed episode is present.

In a clinical overview of ICD-10 and related criteria, the article states: "In bipolar I disorder, depressive episodes often occur but are not required for diagnosis; the defining feature is at least one manic episode." It contrasts this with bipolar II, where a history of at least one major depressive episode and one hypomanic episode is necessary and no history of a full manic episode is allowed.

According to DSM-5-TR, bipolar I disorder is defined by the occurrence of at least one manic episode; major depressive episodes frequently occur but are not required for the diagnosis. Bipolar II disorder is defined by at least one hypomanic episode and at least one major depressive episode, with no history of a full manic episode. Both disorders are conceptualized as involving episodic shifts between elevated (manic or hypomanic) and depressed mood states over time, though an individual patient may present at a given time with only one pole.