Depression: Symptoms, Causes, and Treatment

What Depression Is

Everyone feels sad or low at times, and those feelings usually pass. Depression — also called major depression, major depressive disorder, or clinical depression — is different: it involves severe, persistent symptoms that affect how a person feels, thinks, and manages daily life, including sleep, appetite, and the ability to function at work or in relationships. Depression can affect anyone regardless of age, sex, income, culture, or background, and research points to a combination of genetic, biological, environmental, and psychological factors contributing to it.

• Major depression: depressed mood or loss of interest most of the day, nearly every day, for at least two weeks
• Persistent depressive disorder: less severe symptoms lasting considerably longer, generally at least two years
• Seasonal affective disorder: depressive symptoms that follow a seasonal pattern
• Depression with symptoms of psychosis: a more severe presentation that can include delusions or hallucinations
• Depression as part of bipolar disorder, alternating with periods of mania or hypomania

Common Signs and Symptoms

Depression symptoms extend well beyond persistent sadness. Common signs include hopelessness, irritability or restlessness, loss of interest in things a person used to enjoy, fatigue, difficulty concentrating or making decisions, sleep disturbances (too little or too much), changes in appetite or weight, and physical symptoms like headaches or digestive issues that don't have a clear physical cause. Increased use of alcohol or drugs is itself a recognized behavioral sign of depression, alongside becoming withdrawn from others or having difficulty meeting everyday responsibilities.

Not everyone experiences the same combination or severity of symptoms — some people have only a few, others experience many, and how depression presents can vary meaningfully by age. Children may seem anxious or physically unwell rather than sad; teens may become irritable, withdrawn, or struggle at school; older adults sometimes report a lack of emotion or physical complaints rather than a depressed mood, which can make depression harder to recognize later in life.

How Depression Is Diagnosed

A depression diagnosis generally requires symptoms present most of the day, nearly every day, for at least two weeks, with a depressed mood or loss of interest as one of the defining features (children and teens may show irritability rather than sadness). Diagnosis is made clinically — through a conversation with a health care provider about symptoms, timing, and impact on daily life — since there's no single lab test or scan that confirms depression on its own. Providers also generally rule out medical conditions, like thyroid disorders, that can produce similar symptoms.

Why Depression and Substance Use So Often Occur Together

The connection between depression and substance use runs in multiple directions. Some people describe using alcohol or other substances to temporarily relieve depressive symptoms, even though sustained use tends to worsen depression over time rather than resolve it. Separately, depression is a well-documented feature of withdrawal from several substances — the "crash" that follows heavy stimulant use, for example, commonly includes depressive symptoms severe enough to resemble a major depressive episode, and depression can persist for weeks into early recovery from alcohol or opioid use as well.

Because of this overlap, distinguishing depression that exists independently from depression tied to withdrawal is an important part of accurate treatment planning, and co-occurring depression is generally addressed directly rather than assumed to resolve on its own once substance use stops.

How Depression Is Treated

Depression treatment typically involves psychotherapy, medication, or both, with the right combination shaped by symptom severity and individual circumstances. For milder depression, psychotherapy is often tried first, with medication added if needed; moderate to severe depression is generally treated with medication as part of the initial plan. Psychotherapy approaches with strong evidence behind them include cognitive behavioral therapy (CBT), which helps people identify and change unhelpful thought and behavior patterns, and interpersonal therapy (IPT), which focuses on relationship and life-event factors that affect mood.

Antidepressant medications work by changing how the brain processes certain mood-related chemicals, and generally take four to eight weeks to reach full effect — sleep, appetite, and concentration often improve before mood does, which is part of why giving a medication adequate time is considered important before judging whether it's working. When depression doesn't improve after trying at least two antidepressants, it's classified as treatment-resistant; options at that point include esketamine, a rapid-acting FDA-approved nasal spray medication, or combining an antidepressant with a second medication. Brain stimulation therapies, including electroconvulsive therapy (ECT) and repetitive transcranial magnetic stimulation (rTMS), are generally used when psychotherapy and medication haven't produced sufficient improvement, though they can be used earlier in severe, life-threatening cases.