There are several different types of depression, which have different symptoms and causes ranging from mild to severe:

• Major depression — also known as clinical depression or unipolar depression, refers to distinct episodes of depression lasting 2 weeks or more that have a negative impact on everyday functioning.
• Melancholia — a less common and more severe form of depression which causes slowed movements and a complete loss of pleasure in everything.
• Psychotic depression — a rare form of depression accompanied by a distorted view of reality, such as delusional thinking (negative and untrue beliefs) and hallucinations (e.g. hearing voices).
• Antenatal and postnatal depression — triggered by pregnancy or childbirth. Up to 10% of pregnant women and 16% in the 3 months after birth will suffer from depression.
• Bipolar disorder — involves distinct periods of depression and elated moods known as mania. It was previously known as manic depression.
• Cyclothymia — a chronic disorder with at least 2 years of alternating periods of low and high moods that are less severe than major depression or mania. It can be described as a mild form of bipolar disorder.
• Seasonal affective disorder (SAD) — periods of depression that occur in particular seasons, particularly winter, and related to low levels of sunlight. This condition is most common in places with long nights in winter, such as those regions closer to the north pole.

Identifying the type of depression is important in determining the most effective treatment. Depression is treatable and the earlier treatment begins the better.