DisclosureWe earn commission on partner links; ranking is set by our evidence-based methodology — not advertisers. Read policy
Medically reviewed & updated
Medically reviewed by the HealthVetted Medical Board
Depression (clinically, major depressive disorder) is a common but serious mood disorder that causes a persistent low mood or loss of interest in activities, lasting at least two weeks and interfering with how a person sleeps, eats, works, and feels. It is a treatable medical condition — not a personal weakness or a passing bad mood — and most people improve substantially with the right combination of therapy, lifestyle changes, and, when needed, medication.
Depression is a mental health condition defined by a depressed mood or a loss of pleasure and interest (called *anhedonia*) that is present most of the day, nearly every day, for at least two weeks, alongside a cluster of physical and cognitive symptoms. It is distinct from ordinary sadness or grief: depression is more pervasive, more persistent, and disproportionate in its effect on daily functioning.
The most common diagnosis is major depressive disorder (MDD), coded as F32 (single episode) or F33 (recurrent) in ICD-10. But depression is an umbrella that includes several related conditions:
Depression is genuinely common. According to the National Institute of Mental Health, drawing on the 2021 National Survey on Drug Use and Health, an estimated 8.3% of U.S. adults — about 21.0 million people — had at least one major depressive episode that year, with the highest rate (18.6%) among adults aged 18 to 25 (NIMH). Among adolescents aged 12 to 17, the past-year rate was 20.1% (NIMH). Depression is roughly twice as common in women as in men.
There is no single cause. Depression results from an interaction of biological, psychological, and environmental factors. The older "chemical imbalance" explanation — the idea that depression is simply too little serotonin — is now understood to be an oversimplification; current research points to a more complex picture involving genetics, brain circuitry, stress hormones, inflammation, and neuroplasticity (StatPearls).
Well-established risk factors include:
Importantly, depression also occurs in people with no identifiable trigger and no obvious "reason." That does not make it less real or less treatable.
Depression affects mood, body, and thinking. The core symptom is either a low mood or a loss of interest, but it rarely travels alone. Common features include:
Symptoms can look different across people. Some experience depression mainly as physical complaints — unexplained aches, digestive problems, or exhaustion. In men, depression may present more as irritability, anger, or reckless behavior. In older adults, memory problems and physical symptoms can mask the mood component. In children and teens, irritability is often more prominent than sadness.
There is no blood test or brain scan that diagnoses depression. Diagnosis is clinical, based on a structured interview and standardized criteria, usually with lab work to rule out other causes.
Clinicians use the DSM-5-TR criteria for major depressive disorder. A diagnosis requires five or more of nine specified symptoms present during the same two-week period, representing a change from previous functioning. Critically, at least one of the five must be either (1) depressed mood or (2) loss of interest or pleasure. The symptoms must cause clinically significant distress or impairment and must not be better explained by a substance, a medical condition, or another disorder. A history of a manic or hypomanic episode points toward bipolar disorder rather than MDD and must be ruled out (StatPearls).
The most widely used screening instrument is the PHQ-9 (Patient Health Questionnaire-9), a nine-item self-report scale mapping directly onto the DSM-5 criteria. It scores from 0 to 27:
A score of 10 or higher is the commonly used threshold suggesting probable major depression and warranting further evaluation. A shorter two-item version, the PHQ-2, is often used as a first-pass screen. The U.S. Preventive Services Task Force (USPSTF) recommends screening for depression in the adult population, including pregnant and postpartum people and older adults (USPSTF, 2023, grade B).
Because thyroid disease, anemia, vitamin B12 deficiency, and other conditions can mimic depression, clinicians often order labs such as thyroid function tests and a complete blood count. They will also review medications, substance use, and sleep.
Depression is highly treatable, and treatment is matched to severity. Mild depression may respond to lifestyle changes and psychotherapy alone; moderate to severe depression usually warrants medication, therapy, or both. The general principle is to start with the least invasive effective option and escalate as needed.
For mild-to-moderate depression, the following have genuine evidence behind them and are recommended as a foundation (often alongside other treatment):
Psychotherapy is first-line and as effective as medication for many people with mild-to-moderate depression. The best-supported forms include cognitive behavioral therapy (CBT), interpersonal therapy (IPT), and behavioral activation.
Evidence here is limited and OTC products are not substitutes for treatment of moderate-to-severe depression. Some agents have modest supporting data — for example, *St. John's wort* has shown benefit for mild depression in some studies but carries serious drug interactions (including with antidepressants, birth control, and blood thinners) and should not be combined with prescription antidepressants. Omega-3 fatty acids and vitamin D have mixed evidence. Bright-light therapy is well supported specifically for seasonal affective disorder. Anyone considering supplements should review them with a clinician or pharmacist first.
When medication is indicated, guidelines from the American Psychiatric Association and others identify several first-line antidepressant classes. No single class is clearly superior overall; selection is individualized based on side-effect profile, other symptoms, and patient preference:
Older classes — tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs) — remain effective but are generally not first-line because of side effects, overdose risk, and dietary or drug interactions. They are reserved for cases that don't respond to safer options.
Two practical points patients should know: antidepressants typically take two to six weeks to show meaningful benefit, and they should not be stopped abruptly because of discontinuation symptoms — tapering under medical supervision is important. Regulators also require a warning that antidepressants may increase suicidal thoughts in people under 25, especially early in treatment, which is one reason close follow-up matters in the first weeks.
When two adequate medication trials don't work — referred to as treatment-resistant depression — additional options exist:
Depression cannot always be prevented, but risk and recurrence can be reduced. Because a prior episode strongly predicts future ones, long-term management focuses on *relapse prevention*: maintaining treatment for an adequate duration, recognizing early warning signs, protecting sleep, staying physically active, limiting alcohol, and keeping social and professional supports in place.
For people who have had a single episode, guidelines generally recommend continuing antidepressant treatment for several months after symptoms resolve to reduce relapse risk. For those with recurrent episodes, longer-term or maintenance treatment is often advised. Psychotherapy — particularly CBT and mindfulness-based cognitive therapy — has evidence for reducing relapse even after medication is stopped. Treating coexisting conditions (anxiety, chronic pain, substance use, thyroid disease) also improves outcomes.
See a healthcare professional if low mood or loss of interest lasts two weeks or longer, or if symptoms interfere with work, relationships, or daily functioning. Earlier evaluation is better — depression tends to respond better the sooner it is treated.
Seek emergency help immediately for any of these red flags:
In the United States, anyone in crisis can call or text 988 to reach the Suicide and Crisis Lifeline, available 24/7, or go to the nearest emergency department. These warning signs are medical emergencies, not moments to "wait and see."
The prognosis for depression is generally good, and this is the most important message: most people who receive adequate treatment improve, and many recover fully. With appropriate therapy and/or medication, a large proportion of people achieve significant symptom reduction or full remission, though it sometimes takes more than one treatment adjustment to find the right fit.
Depression can be episodic (one or a few discrete episodes) or recurrent, and untreated episodes tend to last longer and recur more often. The realistic outlook: depression is a chronic-relapsing condition for some and a one-time event for others, but in both cases it is manageable. Staying engaged with treatment, building relapse-prevention habits, and seeking help early during warning signs are the factors most associated with lasting recovery.
Is depression a chemical imbalance? Not exactly. The simple "low serotonin" model is now considered outdated. Depression involves a combination of genetics, brain circuit function, stress and hormonal systems, inflammation, life events, and psychology. Antidepressants do affect brain chemistry, but that doesn't mean depression is caused by a single chemical deficiency.
How long do antidepressants take to work? Most people don't feel the full effect for two to six weeks. Some early changes (sleep, appetite, energy) may come first, with mood improving later. If there's no meaningful benefit after an adequate trial at an adequate dose, clinicians often adjust the dose or switch agents. Don't stop abruptly — taper under medical guidance.
Can depression go away on its own? Some milder episodes do resolve over time, but this is unpredictable, and waiting carries risk — untreated depression can last longer, deepen, and recur. Treatment shortens episodes and lowers relapse risk, so professional evaluation is worthwhile rather than simply waiting it out.
What's the difference between depression and just feeling sad? Sadness is a normal, usually temporary response to a specific event and doesn't typically derail your functioning. Clinical depression is more persistent (two weeks or more), more pervasive, and impairs daily life — affecting sleep, appetite, concentration, energy, and self-worth — often without a clear external trigger.
Is depression genetic? Genetics contribute meaningfully — heritability is estimated around 40%, and a family history raises risk — but genes are not destiny. Many people with a family history never develop depression, and many with depression have no family history. Environment, stress, and life circumstances play a large role.
---
*This page is for general education and is not medical advice. Depression is a medical condition that should be evaluated and treated by a qualified clinician. If you are in crisis or thinking about suicide, call or text 988 (U.S.) or go to your nearest emergency department.*
Sadness is a normal, temporary emotion that usually lifts on its own. Depression is a medical condition in which low mood or loss of interest persists most of the day, nearly every day, for at least two weeks and interferes with daily functioning. It often brings physical symptoms such as fatigue, sleep and appetite changes, and trouble concentrating, and typically does not improve simply by trying to 'snap out of it.'
There is no blood test for depression. A clinician diagnoses it through a clinical interview and your symptom history, using DSM-5 criteria: five or more symptoms — including depressed mood or loss of interest — present most days for at least two weeks and causing impairment. Screening questionnaires like the PHQ-9 may be used, and the clinician will rule out medical causes such as thyroid disease and any history of mania.
Antidepressants usually take about 4 to 8 weeks to reach their full effect, though some people notice improvements in sleep, appetite, or energy sooner. It is important not to stop taking them without talking to your prescriber, even once you feel better. If a medication does not help or causes side effects, a clinician can adjust the dose or try a different one.
Psychotherapy such as cognitive behavioral therapy (CBT) and interpersonal therapy (IPT), antidepressant medication, or a combination are the main evidence-based treatments. Milder depression may respond to therapy alone, while moderate to severe depression often improves more with combined medication and therapy. For treatment-resistant cases, options include esketamine and brain stimulation therapies like ECT and transcranial magnetic stimulation (rTMS).
Yes, supportive lifestyle measures can help — regular physical activity, consistent sleep, balanced nutrition, limiting alcohol, and maintaining social connections all support mental health and may ease milder symptoms. However, lifestyle changes are not a substitute for professional treatment in moderate or severe depression. They work best alongside therapy and, when needed, medication recommended by a clinician.
See a doctor or mental health professional if low mood or loss of interest lasts more than two weeks, gets worse, or disrupts your work, relationships, or daily routine. Seek help urgently if you have thoughts of death, self-harm, or suicide. In the U.S., call or text the 988 Suicide and Crisis Lifeline at any time, or call 911 for a life-threatening emergency.
This page is for general information and is not medical advice. Always consult a qualified clinician about diagnosis and treatment. Individual results vary.