Is characterized by one or more Major Depressive Episodes (i.e at least 2 weeks of depressed mood or loss of interest accompanied by at least four weeks of additional symptoms of depression.) The essential feature of Major Depressive Episode is a period of at least 2 weeks during which there is either depressed mood or the loss of interest or pleasure in nearly all activities. In children and adolescents, the mood may be irritable rather than sad. The individual must also experience at least four additional symptoms drawn from a list that includes changes in appetite or weight; sleep and psychomotor activity; decreased energy; feelings of worthlessness or guilt; difficulty thinking, concentrating or making decisions; or recurrent thoughts of death or suicidal ideation, plans, or attempts. The mood in a Major Depressive Episode is often described by the person as depressed, sad, hopeless, or "down in the dumps". In some cases, sadness may be denied at first, but may subsequently be elicited by interview. Some individuals emphasise somatic complaints (e.g. bodily aches and pains) rather than reporting feelings of sadness. Many report or exhibit increased irritability (e.g. persistent anger, a tendency to respond to events with angry outbursts or blaming others, or an exaggerated sense of frustration over minor matters). In children or adolescents, an irritable or cranky mood may develop rather than a sad or dejected mood.

Loss of interest or pleasure is nearly always present, at least to some degree. Individuals may report feeling less interested in hobbies, "not caring anymore" or not feeling any enjoyment in activities that were previously considered pleasurable. In some individuals, there is a significant reduction from previous levels of sexual interest or desire.

Appetite is usually reduced and many individuals feel that they have to force themselves to eat. Others may have increased appetite and may crave specific foods.

The most common sleep disturbance associated with Major Depressive Episode is insomnia. Individuals typically have middle insomnia (i.e. waking up during the night and being unable to return to sleep) or terminal insomnia (i.e. waking too early and being unable to return to sleep). Initial insomnia (i.e. difficulty falling asleep) may also occur. Less frequently, individuals present with oversleeping (hypersomnia) in the form of prolonged sleep episodes at night or increased daytime sleep.

Is characterized by at least 2 years of depressed mood for more days than not, accompanied by additional depressive symptoms that do not meet criteria for a Major Depressive Episode. During periods of depressed mood, at least two of the following additional symptoms are present: poor appetite or overeating, insomnia or hypersomnia, low energy or fatigue, low self-esteem, poor concentration or difficulty making decisions, and feelings of hopelessness. Individuals may note the prominent presence of low interest and self-criticism, often seeing themselves as uninteresting or incapable. Because these symptoms have become so much a part of the individual's day-to-day experience (e.g. "I've always been this way", "That's just how I am"), they are often not reported unless directly asked about by the interviewer.

A Manic Episode is defined by a distinct period during which there is an abnormally and persistently elevated, expansive or irritable mood. This period of abnormal mood must last at least 1 week (or less if hospitalization is required). The mood disturbance must be accompanied by at least three additional symptoms from a list that includes inflated self-esteem or grandiosity (grandiose delusions are common), decreased need for sleep, pressure of speech, flight of ideas, distractibility, increased involvement in goal-directed activities or psycho-motor agitation and excessive involvement in pleasurable activities with high potential for painful consequences. The elevated mood of a manic episode may be described as euphoric, unusually good, cheerful or high. Although the person's mood may initially have an infectious quality for the involved observer, it is recognized as excessive by those who know the person well. The expansive quality of the mood is characterized by unceasing and indiscriminate enthusiasm for interpersonal, sexual or occupational interactions. For example, the person may spontaneously start extensive conversations with strangers in public places or a salesperson may telephone strangers at home in the early morning hours to initiate a sales. Although elevated mood is considered the prototypical symptom, the predominant mood disturbance may be irritability, particularly when the person's wishes are thwarted.

A Mixed Episode is characterized by a period of time (lasting at least 1 week) in which the criteria are met for the Manic Episode and for the Major Depressive Episode nearly every day. The individual experiences rapidly alternating moods (sadness, irritability, euphoria) accompanied by symptoms of Manic Episode and a Major Depressive Episode. The symptom presentation frequently includes agitation, insomnia, appetite dysregulation, psychotic features and suicidal thinking. The disturbance must be sufficiently severe to cause marked impairment in social or occupational functioning or to require hosptialization or it is characterized by the presence of psychotic features.

A Hypomanic Episode is defined as a distinct period during which there is an abnormally and persistently elevated, expansive, or irritable mood that lasts at least 4 days. This period of abnormal mood must be accompanied by at least three additional symptoms from a list that includes inflated self-esteem or grandiosity (non-delusional), decreased need for sleep, pressure of speech, flight of ideas, distractibility, increased involvement in goal-directed activities or psycho-motor agitation, excessive involvement in pleasurable activities that have a high potential for painful consequences. This list of additional symptoms is identical to those that define a Manic Episode except that delusions or hallucinations cannot be present.

Bipolar I Disorder:

Is characterzied by one or more Manic or Mixed Episodes, usually accompanied by Major Depressive Episodes.

Bipolar II Disorder:

Is characterized by one or more Major Depressive Episodes accompanied by at least one Hypomanic Episode.

Is characterized by at least 2 years of numerous periods of hypomanic symptoms that do not meet criteria for a Manic Episode and numerous periods of depressive symptoms that do not meet criteria for a Major Depressive Episode.

Is characterized by a prominent and persistent disturbance in mood that is judged to be a direct physiological consequence of a drug of abuse, a medication, another somatic treatment for depression or toxin exposure.