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Depression (also known as major depressive disorder or clinical depression) is one of the most common mental health problems worldwide. It is more than simply feeling sad — it is a serious condition that affects how a person thinks, feels, and behaves, and it can significantly impair their ability to function in daily life.
Depression is a mood disorder characterised by persistent feelings of sadness, hopelessness, and a loss of interest or pleasure in activities that were previously enjoyable. To be diagnosed with depression, these symptoms must be present for at least two weeks and must cause significant distress or impairment in functioning.
The characteristics of depression can be categorised into emotional, behavioural, and cognitive symptoms:
| Symptom | Description |
|---|---|
| Persistent sadness | Feeling sad, empty, or tearful most of the day, nearly every day |
| Loss of interest or pleasure | No longer enjoying activities that were previously pleasurable (anhedonia) |
| Feelings of worthlessness | Excessive guilt, feeling like a burden to others |
| Hopelessness | Feeling that things will never get better |
| Irritability | Becoming easily frustrated or angry |
| Anxiety | Feeling nervous, restless, or on edge |
| Symptom | Description |
|---|---|
| Social withdrawal | Avoiding social contact, cancelling plans, isolating oneself |
| Reduced activity | Doing less, loss of motivation, neglecting responsibilities |
| Sleep disturbance | Insomnia (difficulty sleeping) or hypersomnia (sleeping too much) |
| Appetite changes | Eating too little or too much, leading to weight loss or gain |
| Psychomotor changes | Slowed speech and movement, or restlessness and agitation |
| Self-harm or suicidal behaviour | In severe cases, thoughts of death or suicide, or self-harming behaviour |
| Symptom | Description |
|---|---|
| Negative self-concept | Negative view of oneself — "I'm a failure," "I'm worthless" |
| Difficulty concentrating | Unable to focus, make decisions, or remember things |
| Negative thinking | Focusing on negative aspects of life, expecting the worst |
| Cognitive biases | Selective attention to negative information; ignoring positive experiences |
| Rumination | Repeatedly going over negative thoughts and events |
| Type | Description |
|---|---|
| Major depressive disorder | At least 2 weeks of persistent symptoms; may occur as a single episode or recurrently |
| Persistent depressive disorder (dysthymia) | Milder but chronic (lasting at least 2 years) |
| Seasonal affective disorder (SAD) | Depression related to seasonal changes, typically in winter |
| Postnatal depression | Depression occurring after giving birth |
AQA specifies that you should know the distinction between unipolar and bipolar depression.
Bipolar disorder typically requires different treatment from unipolar depression, often including mood stabilisers such as lithium, rather than standard antidepressants alone, because antidepressants can trigger manic episodes in people with bipolar disorder. UK NHS guidance (NICE) recommends specialist mental-health service involvement for bipolar disorder.
The International Classification of Diseases (ICD-11), used by the NHS, specifies that a depressive episode requires at least two weeks of persistent symptoms. Core symptoms are:
Additional symptoms include:
Depression is classified as mild, moderate or severe according to the number and intensity of symptoms and the degree of functional impairment.
flowchart TD
A[Symptoms present] --> B{At least 2 weeks?}
B -->|No| C[Not a depressive episode]
B -->|Yes| D{Core symptoms present?}
D -->|Low mood / anhedonia / fatigue| E{Additional symptoms?}
E -->|Sleep, appetite, concentration, worthlessness| F{Functional impairment?}
F -->|Yes| G[Depressive episode: ICD-11]
G --> H[Classify by severity]
H --> I[Mild]
H --> J[Moderate]
H --> K[Severe]
According to NHS Digital and the Office for National Statistics (ONS), approximately 1 in 6 adults in England experience a common mental health problem such as depression or anxiety in any given week. Rates rose notably during the COVID-19 pandemic. Depression is one of the leading causes of disability in the UK, contributing to lost work, education and wellbeing. Young women aged 16–24 have particularly high rates. Support is available from the NHS, NHS Talking Therapies, Mind and the Samaritans (116 123).
A serious feature of depression is increased suicide risk. UK suicide prevention work is led by the NHS, the Samaritans, Zero Suicide Alliance, the Campaign Against Living Miserably (CALM) and the Department of Health and Social Care. GCSE students should know that:
Treatments for depression — whether CBT, medication or combined care — aim to reduce both symptoms and suicide risk, and clinicians monitor risk throughout treatment.
Depression can occur at any age but shows different patterns and presentations across the life course:
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