Major depressive disorder (MDD)

What major depressive disorder actually is

Major depressive disorder, often called clinical depression, is the formal diagnosis behind what most people mean by depression. It’s defined by a period of at least two weeks in which someone has either a persistently low or sad mood, a loss of interest or pleasure in activities, or both, for most of the day, nearly every day.

Alongside that, the diagnosis requires several additional symptoms. These can include changes in sleep or appetite, fatigue or low energy, trouble concentrating, feelings of worthlessness or guilt, slowed or restless movement, and thoughts of death or suicide. By clinical definition, these symptoms represent a clear change from how the person usually functions and interfere with daily life.

Depression often runs a course of episodes. Some people have a single episode, while others experience recurring episodes over time. The condition involves a mix of biological, psychological, and environmental factors.

What major depressive disorder can feel like

People often describe it as more than sadness. Many feel a heavy flatness, where things that used to bring joy now feel empty, an experience known as anhedonia. Simple tasks can feel enormous, and the day can seem to stretch on without relief.

The mind frequently turns harsh and repetitive, replaying perceived failures or circling hopeless thoughts, a pattern related to rumination. Sleep often breaks down, whether sleeping far too little or too much, and energy can drain away so thoroughly that getting out of bed feels difficult.

What major depressive disorder isn’t

MDD isn’t ordinary sadness or a rough week. Everyone feels down sometimes, but clinical depression is a sustained pattern that lasts at least two weeks and disrupts functioning.

It also isn’t a weakness, a lack of willpower, or something a person can simply decide their way out of. It’s a recognized medical condition with well-studied treatments. And it’s distinct from bipolar disorder, where periods of depression alternate with manic or hypomanic episodes, a difference that matters for treatment.

Related terms you’ll see next

Depression is the everyday term for the experience this diagnosis describes. Anhedonia is the loss of pleasure that’s central to many episodes. Rumination describes the repetitive negative thinking that often comes with it. Behavioral activation is an evidence-based therapy approach for depression.

When to seek professional care

If low mood or loss of interest has lasted two weeks or more and is interfering with daily life, an evaluation is worthwhile. A clinician can confirm whether the pattern fits major depressive disorder and discuss therapy and medication options. If you’re having thoughts of suicide or self-harm, seek help right away. If you’re in crisis, call or text 988 in the United States.