Depression: A Disorder Affecting Mood, Thought and Function

Depression is more than temporary sadness or an isolated period of low mood. It is a sustained disorder affecting emotion, thinking, physical functioning and daily life. Diagnosis depends on symptom pattern, persistence, severity and impairment, while treatment is matched to individual need, preference and safety.

What depression is Depression is a mental health disorder affecting mood, interest, thinking, physical functioning and behaviour. It is sometimes called a depressive episode or major depression, depending on the diagnostic system and clinical context. The condition exists along a continuum, from less severe episodes to severe illness with major functional impairment. Depression is treatable, and recovery is possible even after severe or recurrent episodes. Depression is not simply sadness Sadness is a normal human emotion following disappointment, conflict, loss or other difficult experiences. Ordinary sadness often changes with circumstances and may coexist with pleasure, hope, connection and normal daily functioning. Clinical depression is more persistent and pervasive, affecting several areas of life rather than one emotional moment. The distinction depends on the whole pattern, not whether there is an understandable reason for feeling distressed. Grief and depression Grief is a natural response to bereavement and may involve intense sadness, yearning, poor sleep and temporary reduced concentration. Grief often comes in waves linked to reminders, while positive memories and emotional connection may remain possible. Depression can occur during bereavement and should not be dismissed because a loss has happened. Persistent anhedonia, severe worthlessness, pervasive hopelessness, marked functional decline or suicidal intent requires clinical assessment. The diagnostic threshold Diagnostic systems require a sustained cluster of symptoms rather than one complaint in isolation. Depressed mood or loss of interest is usually present most of the day, nearly every day, for at least two weeks. The DSM framework requires at least five symptoms, including depressed mood or loss of interest or pleasure. Symptoms must cause clinically significant distress or impairment and should not be explained better by another condition. Diagnosis is more than counting symptoms NICE advises a comprehensive assessment that does not rely only on a questionnaire or symptom count. Clinicians consider symptom intensity, frequency, duration, previous episodes and the course of the current illness. They also assess work, education, relationships, self care, parenting, social participation and physical functioning. A person with fewer symptoms can still need substantial help when impairment, risk or duration is significant. The two core symptoms The first core symptom is persistent depressed mood, which may feel like sadness, emptiness, hopelessness or emotional numbness. The second is anhedonia, meaning reduced interest or pleasure in activities that were previously meaningful. At least one core symptom is usually needed for a depressive episode diagnosis. Some people describe loss of motivation or connection more readily than they describe feeling sad. Depressed mood Depressed mood can involve tearfulness, heaviness, irritability, emptiness or feeling unable to experience emotional relief. Children and younger people may appear irritable rather than obviously sad. Some adults describe feeling emotionally flat or disconnected instead of visibly distressed. Cultural background and language influence how people describe internal experiences and whether they seek help. Anhedonia Anhedonia is reduced interest, enjoyment or emotional reward from activities and relationships. A person may stop hobbies, avoid friends, lose sexual interest or feel detached from family life. They may continue activities through obligation while experiencing little satisfaction. Anhedonia is clinically important because it distinguishes depression from many brief reactions to stress. Reduced energy and fatigue Depression commonly causes persistent tiredness, reduced stamina and difficulty initiating ordinary tasks. Simple activities such as washing, cooking, answering messages or attending work can feel disproportionately demanding. Fatigue can also result from anaemia, thyroid disease, infection, sleep disorders and many medicines. Assessment therefore considers both depression and physical causes rather than assuming one explanation. Sleep disturbance Depression can cause difficulty falling asleep, repeated waking, early morning waking or excessive sleep. Sleep may feel unrefreshing even after many hours in bed. Poor sleep can worsen concentration, emotional regulation and suicidal thinking. Sleep symptoms are treated within the depression plan rather than being assumed to be a separate diagnosis. Appetite and weight change Appetite can decrease or increase during depression. Some people lose weight unintentionally, while others eat more and gain weight. Changes can reflect altered reward, anxiety, reduced self care or disrupted daily routines. Marked weight loss, dehydration or inability to eat requires urgent physical and mental health assessment. Concentration and decision making Depression can impair attention, memory, processing speed and decision making. People may reread information, forget appointments or feel unable to make ordinary choices. These changes can be mistaken for laziness, dementia or lack of motivation. In older adults, cognitive symptoms require particular care because depression, delirium and neurocognitive disorders can overlap. Psychomotor change Psychomotor retardation means observable slowing of movement, speech and responses. Psychomotor agitation means visible restlessness, pacing, hand wringing or inability to remain still. These changes are more than a private feeling of being slowed or tense. Marked psychomotor disturbance can indicate severe depression and increased care needs. Guilt and worthlessness Depression can produce excessive guilt, self blame and beliefs of being useless or burdensome. These thoughts may be disproportionate to events and resistant to reassurance. Severe guilt can become delusional, with fixed false beliefs about causing disaster, punishment or ruin. Worthlessness and burdensomeness are important suicide risk signals and should be explored directly. Hopelessness and suicidal thoughts Hopelessness means believing that the future cannot improve or that no effective help exists. Suicidal thoughts range from passive wishes not to wake up to active ideas, plans, preparation and intent. Clinicians ask directly about these thoughts because careful questioning does not create suicidal intent. Active planning, intent, inability to stay safe or rapidly escalating risk requires urgent same day assessment. Functional impairment Depression affects more than subjective mood. It can disrupt hygiene, nutrition, medication use, employment, education, relationships, parenting and financial management. Some people maintain outward responsibilities at considerable internal cost and collapse when alone. Function should therefore be assessed sensitively rather than inferred from appearance or employment status. Depression severity is a continuum NICE describes severity through symptoms, duration and impact on personal and social functioning. Traditional categories are mild, moderate and severe depression. Current NICE treatment guidance groups subthreshold and mild episodes as less severe depression. Moderate and severe episodes are grouped as more severe depression for treatment recommendations. Mild depression Mild depression involves a limited symptom burden and relatively preserved functioning, although distress can still be substantial. A person may continue daily responsibilities with increased effort and reduced enjoyment. Risk, recurrence history and duration can make an apparently mild episode clinically important. Treatment commonly begins with less intrusive psychological or supported self management options when safe and acceptable. Moderate depression Moderate depression causes a broader symptom cluster and clearer difficulty maintaining ordinary roles. Work, relationships, self care and decision making may become significantly impaired. Treatment options include structured psychological therapy, antidepressant medication or both according to preference and clinical need. The boundary between moderate and severe illness is not determined by one questionnaire score alone. Severe depression Severe depression causes intense symptoms, marked functional impairment or significant risk. A person may stop eating, drinking, speaking, moving, working or caring for themselves. A severe episode can be described as with or without psychotic features. Catatonia can also occur. Specialist care, combination treatment or urgent hospital assessment may be necessary. Depression with psychotic features Psychotic depression includes hallucinations or delusions occurring during a severe depressive episode. Themes commonly involve guilt, deserved punishment, poverty, illness, nihilism or persecution. Psychotic beliefs are experienced as reality rather than ordinary negative thoughts. NICE recommends specialist mental health referral and consideration of antidepressant plus antipsychotic treatment. Catatonia Catatonia is a serious syndrome involving marked disturbance of movement, responsiveness and behaviour. Features can include stupor, mutism, posturing, negativism, rigidity or severe purposeless agitation. It can occur with severe depression, bipolar disorder, psychosis, neurological disease or medical illness. Suspected catatonia requires urgent hospital assessment because dehydration, thrombosis, infection and other complications can develop. Bipolar depression must be considered A depressive episode can be part of bipolar disorder rather than unipolar depression. Clinicians ask about previous periods of unusually elevated or irritable mood, reduced need for sleep, increased activity and impulsive behaviour. Antidepressant treatment without recognising bipolar disorder can be ineffective or contribute to mood destabilisation in some people. A history suggesting mania or hypomania requires appropriate specialist assessment. Depression is not a simple chemical imbalance Depression cannot be explained accurately as one neurotransmitter being too low. Brain signalling changes are involved, but they interact with genetics, development, stress responses, hormones, physical illness and social experience. Antidepressants modify neuronal signalling, but their benefit does not prove a single chemical deficiency cause. A biopsychosocial explanation is more accurate and avoids blaming either biology or personal circumstances alone. Biological contributors Genetic susceptibility contributes to depression, particularly when close relatives have experienced recurrent illness. Sleep disruption, pain, inflammation, hormonal change and altered stress response systems can influence vulnerability. Pregnancy, the postnatal period, perimenopause and some endocrine disorders can affect mood. Biological risk increases probability but does not make depression inevitable. Psychological contributors Harsh self criticism, rumination, hopeless thinking and avoidance can maintain depressive symptoms. Early adversity, trauma, insecure relationships and previous episodes can shape later vulnerability. These patterns are not personal failures and often developed as understandable responses to experience. Psychological treatment helps people recognise and change maintaining cycles without denying social or biological factors. Social contributors Loneliness, discrimination, poverty, debt, insecure housing and unemployment can increase depression risk. Bereavement, relationship breakdown, caregiving burden and workplace stress can precipitate episodes. Migration, cultural dislocation and barriers to healthcare can add further strain. Treatment should address practical and social problems alongside symptoms whenever possible. Risk factors and precipitants Important risk factors include previous depression, family history, trauma, chronic illness, persistent pain and substance misuse. Major life events can precipitate an episode, but depression may also develop without one identifiable trigger. Maintaining factors can differ from the original precipitant. Assessment identifies both vulnerabilities and current problems that can be changed. Physical illness and medicines Stroke, Parkinson's disease, cancer, cardiovascular disease, diabetes and chronic pain are associated with higher depression rates. Hypothyroidism, anaemia, sleep apnoea and other conditions can mimic or worsen depressive symptoms. Corticosteroids, hormonal medicines, interferons and selected neurological treatments can affect mood in some people. Medication should not be stopped independently when depression is suspected. Alcohol and other substances Alcohol can temporarily numb distress but commonly worsens sleep, impulsivity, mood and suicide risk. Cannabis, stimulants, sedatives and other substances can produce or complicate depressive symptoms. Withdrawal states can also alter mood and behaviour. Assessment should be non judgemental and include quantity, pattern, dependence and immediate safety. Protective factors Protective factors can include supportive relationships, responsibilities, cultural or spiritual values and access to responsive healthcare. Problem solving ability, future plans and previous successful coping strategies can also help. Protective factors reduce risk but do not cancel active intent or a dangerous plan. They should support a safety formulation rather than be used to provide false reassurance. Clinical assessment Assessment explores symptoms, duration, function, risk, previous episodes and response to earlier treatment. It also covers mania, psychosis, trauma, anxiety, substance use, physical illness and current medicines. Social circumstances, safeguarding concerns and available support are considered. The clinician develops an individual formulation rather than attaching treatment automatically to a numerical score. Screening questions Clinicians may ask whether someone has often felt down, depressed or hopeless during the previous month. They may also ask whether interest or pleasure in activities has reduced. A positive answer indicates the need for fuller assessment and does not establish a diagnosis alone. People can also volunteer concerns directly without waiting for a screening questionnaire. Questionnaires Measures such as the PHQ 9 can structure symptom review and monitor change over time. They can help a person and clinician see whether treatment is producing meaningful improvement. Scores should be interpreted alongside function, context, risk and communication needs. A questionnaire must not replace direct assessment of suicidal thoughts, psychosis or safeguarding. Physical assessment and investigations There is no blood test or brain scan that confirms depression. Physical examination and targeted tests are selected when symptoms suggest anaemia, thyroid disease, infection or another medical cause. Pregnancy testing, medicine levels or toxicology may be relevant in particular situations. Investigations should be proportionate and should not delay urgent psychiatric care when risk is high. Adjustment disorder Adjustment disorder follows an identifiable stressor and causes distress or functional difficulty exceeding expected adaptation. Symptoms are related closely to the event and may include low mood, anxiety or behavioural change. A person can still develop a full depressive episode after a stressor. The presence of an understandable cause does not exclude depression when diagnostic features are met. Anxiety and depression Anxiety symptoms commonly coexist with depression. Worry, physical tension, panic and avoidance can increase hopelessness and functional impairment. Treatment priorities depend on which disorder is primary and which is creating the greatest risk or disability. A combined formulation often produces better care than forcing every symptom into one category. Trauma related conditions Post traumatic stress disorder can cause emotional numbing, guilt, poor sleep, concentration problems and reduced interest. Intrusive memories, trauma linked avoidance and hyperarousal provide additional clues. Depression and PTSD can coexist and may require coordinated treatment. Trauma should be explored sensitively without forcing detailed disclosure before safety and trust are established. Bereavement and prolonged grief Bereavement does not automatically require medical treatment. Support, cultural mourning practices and time may be appropriate when grief remains within an expected personal pattern. Persistent intense yearning and preoccupation can develop into prolonged grief disorder. Depression may coexist and is assessed through pervasive mood, anhedonia, self worth, function and safety. Depression in older adults Depression in older adults is commonly under recognised and is not an inevitable part of ageing. It may present through pain, fatigue, insomnia, appetite change, memory concerns or reduced physical functioning. Loss, isolation, disability, caring responsibilities and medical illness can contribute. Clinicians should ask directly about mood and pleasure rather than attributing every change to age or disease. Cognitive symptoms in older adults Depression can cause slowed thinking, poor concentration and memory difficulty. Dementia usually produces a progressive cognitive syndrome, while delirium causes an acute fluctuating change in attention and awareness. These conditions can coexist, and sudden confusion is not explained safely by depression alone. Assessment may require collateral history, cognitive testing, medicine review and physical investigation. Antidepressant safety in older adults Older adults can benefit from psychological therapy and antidepressants. Medicine choice considers frailty, falls, bleeding risk, heart rhythm, kidney function and interactions. SSRIs can contribute to hyponatraemia, particularly when diuretics or other risk factors are present. Treatment begins with monitoring rather than assuming older people cannot tolerate effective care. Perinatal depression Perinatal depression occurs during pregnancy or within the first year after childbirth. It can involve low mood, anhedonia, guilt, anxiety, sleep difficulty beyond infant related waking and impaired functioning. Fear of judgement or losing custody can make disclosure difficult. Perinatal services should provide compassionate assessment, timely treatment and attention to the parent, baby and family. Baby blues and postnatal depression The baby blues commonly begin soon after birth and involve tearfulness, emotional sensitivity and mood fluctuation. They usually resolve within several days without progressing into sustained functional impairment. Postnatal depression persists longer, involves a broader depressive syndrome and may begin weeks or months after birth. Severe confusion, mania or psychosis after childbirth is a separate emergency requiring immediate specialist assessment. Treating perinatal depression Facilitated self help can be considered for persistent subthreshold or mild to moderate perinatal depression. Moderate or severe illness can be treated with high intensity psychological therapy, medication or both. The decision considers previous treatment response, current severity, relapse risk, pregnancy stage and personal preference. Specialist perinatal advice is particularly valuable for severe, recurrent or diagnostically complex illness. Antidepressants during pregnancy No decision is completely risk free because untreated depression can harm the pregnant person, functioning and parenting. Medication can also carry fetal, neonatal or maternal risks that vary by drug, dose and pregnancy stage. Stopping an effective antidepressant abruptly can cause withdrawal and relapse. Treatment decisions therefore compare individual benefits and harms rather than assuming pregnancy always requires medication cessation. Breastfeeding and antidepressants Breastfeeding decisions consider medicine transfer into milk, infant health, previous response and the risks of untreated illness. Some antidepressants have more reproductive safety experience than others. A stable effective medicine should not be changed automatically without considering relapse and withdrawal. The baby is monitored when clinically indicated, and the parent's informed feeding choice should be supported. Stepped and matched care Stepped care means offering treatment intensity that matches severity, risk, impairment and previous response. It does not mean withholding effective treatment until a person becomes severely unwell. All options should be discussed through shared decision making. Access, culture, disability, communication, caring duties and treatment preference affect which option is practical. Active monitoring Active monitoring may suit less severe depression when the person prefers no immediate formal treatment and risk is low. It includes discussing concerns, providing information and arranging planned review rather than telling someone simply to wait. Earlier review is needed if symptoms worsen or functioning declines. Active monitoring is inappropriate when significant suicide risk, psychosis or severe self neglect is present. Guided self help Guided self help uses structured materials based on cognitive behavioural or behavioural activation principles. A trained practitioner supports progress and helps overcome barriers. It is less intensive than individual therapy but remains an active treatment. It can be offered in person, digitally or through other accessible formats. Medication in less severe depression NICE does not routinely recommend antidepressants as first line treatment for a new less severe episode. Medication can still be offered when it is the person's informed preference after discussing benefits and harms. Previous severe episodes, persistent symptoms and earlier treatment response also influence the shared decision. Risk and functioning can justify more intensive care even when the symptom count appears limited. Cognitive behavioural therapy Cognitive behavioural therapy, or CBT, examines links between thoughts, emotions, behaviour and physical responses. Treatment can address avoidance, inactivity, rumination, self criticism and hopeless predictions. Sessions include collaborative formulation and practical work between appointments. CBT does not claim that depression is caused simply by incorrect thinking. Interpersonal psychotherapy Interpersonal psychotherapy, or IPT, focuses on relationships and social roles linked to the current depressive episode. It can address grief, role transitions, interpersonal disputes and social isolation. IPT is delivered by a practitioner with specific training and competence. It may suit people whose depression is closely connected with relationship changes or losses. Behavioural activation Behavioural activation helps a person reconnect gradually with routine, valued activity and sources of reinforcement. It addresses the cycle in which low mood leads to withdrawal, reduced reward and deeper depression. Tasks are graded to current capacity rather than demanding immediate normal performance. Behavioural activation can be delivered as guided self help or a structured therapy. Antidepressant medicines Antidepressants alter neuronal signalling and can reduce depressive symptoms. They are not tranquillising medicines and do not create artificial happiness. Benefits are more likely in more severe depression, although individual response varies. Medication choice considers previous response, adverse effects, physical health, interactions, overdose safety and personal preference. SSRIs as first choice Selective serotonin reuptake inhibitors are generally the first choice antidepressants for most adults requiring medication. They are usually better tolerated and safer in overdose than older tricyclic antidepressants. Different SSRIs have different interaction, pregnancy, bleeding, sexual and withdrawal profiles. Selection and dose should be individualised rather than treating the drug class as interchangeable. Timeline to benefit Some adverse effects can appear during the first days, before mood improvement occurs. When an antidepressant is going to work, benefit is usually apparent within four weeks. Sleep, anxiety or energy can change before mood and hopelessness improve. Lack of early benefit prompts review of adherence, diagnosis, dose, side effects and treatment choice. Early review and monitoring Most adults starting antidepressants are reviewed within two weeks. People aged 18 to 25 or with particular suicide concern should usually be reviewed after one week. Monitoring includes mood, agitation, anxiety, suicidal thinking, adherence and adverse effects. Family or carers can support monitoring when the person agrees or immediate safety requires information sharing. Antidepressant adverse effects SSRIs can cause nausea, headache, sleep change, agitation and sexual dysfunction. Bleeding risk can increase, particularly with NSAIDs, antiplatelets or anticoagulants. Some people develop emotional blunting or persistent side effects requiring review. Severe agitation, serotonin toxicity, hyponatraemia or suicidal deterioration requires prompt clinical assessment. Antidepressants and addiction Antidepressants do not usually cause addiction in the sense of craving, intoxication or compulsive dose escalation. The body can still adapt to them, producing physical dependence and withdrawal symptoms after reduction. Difficulty stopping should not be dismissed or described as proof of addictive behaviour. Clear language allows people to understand both the benefits and the real possibility of withdrawal. Discontinuation and withdrawal terminology The term discontinuation symptoms has historically been used for symptoms after reducing antidepressants. NICE now uses withdrawal symptoms because effects can be significant and occasionally prolonged. Possible symptoms include dizziness, nausea, sleep disturbance, agitation and electric shock like sensations. Withdrawal is different from addiction and can also be difficult to distinguish from depressive relapse. Stopping antidepressants Antidepressants should usually be reduced gradually through a personalised taper. The next reduction occurs after previous withdrawal symptoms have resolved or become tolerable. Some people stop over weeks, while others require several months and smaller reductions at low doses. Abrupt stopping, skipped doses and alternate dosing of short acting medicines can provoke withdrawal. Distinguishing withdrawal from relapse Withdrawal often begins within days of a dose reduction and can include unfamiliar physical sensations. Relapse usually develops more gradually and resembles the person's previous depressive syndrome. The distinction is not always clear, and clinical review is important. Severe withdrawal may require returning temporarily to the previous dose and tapering more slowly. Continuing treatment after recovery Antidepressants are commonly continued for at least six months after symptoms remit. Longer continuation may be recommended after recurrent, severe or persistent depression. Relapse prevention decisions consider previous episodes, residual symptoms, consequences of relapse and treatment adverse effects. Psychological relapse prevention therapy can also help recognise warning signs and respond earlier. Combination treatment For more severe depression, NICE places individual CBT combined with an antidepressant among leading first line options. Medication can begin while therapy access is arranged. Combination treatment addresses different maintaining processes and can provide greater benefit for some people. It should remain a shared decision rather than an automatic requirement for every moderate episode. Treating psychotic depression Psychotic depression requires specialist mental health care and coordinated risk assessment. NICE recommends considering an antidepressant combined with an antipsychotic. Psychological therapy is usually introduced after acute psychotic symptoms improve sufficiently. Monitoring focuses on mood, hallucinations, delusions, nutrition, self care and suicide risk. Electroconvulsive therapy Electroconvulsive therapy, or ECT, uses a controlled electrical stimulus under general anaesthesia to produce a therapeutic seizure. NICE recommends considering ECT when a rapid response is needed, depression is life threatening or other treatments have failed. Examples include severe illness with inability to eat or drink, catatonia or very high suicide risk. Memory effects, anaesthetic risk, previous response and informed consent require careful specialist discussion. When treatment does not help A poor response prompts review of diagnosis, adherence, dose, duration and coexisting physical or mental health conditions. Clinicians consider bipolar disorder, substance use, trauma, neurodevelopmental needs and continuing social adversity. Options include switching therapy, changing medication, combining treatments or specialist augmentation. The term treatment resistant should not imply that the person is resistant or responsible for non response. Physical activity and daily routine Regular activity can support mood, sleep and physical health when matched to the person's ability. Exercise is a treatment option for some less severe episodes but is not a moral test or universal cure. Regular meals, sleep routines and reduced alcohol can support recovery. These measures complement rather than replace indicated psychological or medical treatment. Social and practical intervention Debt advice, housing support, workplace adjustments and help with caregiving can reduce maintaining stress. Social prescribing and community connection may reduce isolation for some people. Safeguarding action may be needed when abuse, neglect, exploitation or domestic violence is present. Practical intervention is part of depression care rather than separate from it. Safety planning A safety plan is developed collaboratively when self harm or suicide risk is present. It identifies warning signs, personal coping strategies, supportive contacts and professional crisis services. It also includes reducing access to means where possible and identifying reasons or responsibilities that support survival. The plan should be accessible, reviewed when circumstances change and shared with trusted people when agreed. Risk formulation rather than prediction No checklist can predict individual suicide accurately. Assessment considers current thoughts, intent, planning, past behaviour, mental state, stressors, access to means and support. NICE advises against using risk scales alone to decide treatment or discharge after self harm. Clinical formulation guides proportionate support while recognising that risk can change quickly. Same day crisis assessment Active suicidal intent, a specific plan, recent preparation or inability to maintain safety requires urgent same day crisis assessment. Psychotic depression, catatonia, severe self neglect and rapidly deteriorating function also require urgent specialist review. The person should not be left alone when immediate danger is present. Emergency services are required when there is imminent danger, a serious attempt, violence risk or urgent medical need. Safeguarding Depression can impair a person's ability to protect themselves or care for dependants. Clinicians assess risks involving children, vulnerable adults, domestic abuse, neglect and exploitation. Confidentiality is important but can be overridden when sharing information is necessary to prevent serious harm. Safeguarding should be explained compassionately and should not be used to punish disclosure. Recovery Recovery can involve symptom remission, restored functioning, renewed relationships and improved confidence. Progress is rarely perfectly linear, and temporary difficult days do not prove treatment failure. Goals should reflect what matters to the person rather than only a questionnaire score. Continuing support can help rebuild routines and address consequences accumulated during the episode. Relapse prevention Relapse prevention identifies early warning signs such as sleep change, withdrawal, rumination or reduced self care. A plan records which actions and contacts previously helped. People at higher relapse risk may continue medication, psychological therapy or both. Regular review allows the plan to change as health, pregnancy, relationships and circumstances evolve. The central safety message Depression is diagnosed through sustained symptoms, severity and functional impact rather than temporary sadness alone. Direct questions about suicide, psychosis, self neglect and safeguarding are essential parts of assessment. Less severe depression may respond to supported psychological approaches, while more severe illness often needs medication, therapy or both. Active suicidal intent, psychotic depression, catatonia or inability to meet basic needs requires urgent specialist care.

Depression is a sustained disorder affecting mood, interest, thought, physical functioning and daily life. Diagnosis considers duration, symptom burden and impairment, while treatment combines biological, psychological and social approaches matched to severity, preference and safety.