Overview
Depression is a common mental health condition characterised by persistent low mood, loss of interest or pleasure in activities, and a range of emotional and physical symptoms that interfere with daily life. It is a genuine medical condition, not a weakness or something someone can simply 'snap out of'.
How common is it?
About 1 in 6 adults in the UK experience depression at some point. It is one of the leading causes of disability worldwide.
Causes and risk factors
Depression results from a complex interaction between biological, psychological, and social factors. Brain chemistry, particularly serotonin and noradrenaline systems, is disrupted, but this is a consequence of the condition, not a simple chemical imbalance.
Common risk factors
- Stressful life events (bereavement, job loss, relationship breakdown)
- Family history of depression
- Chronic physical illness
- Previous episodes of depression
- Certain medications (beta-blockers, steroids, some contraceptives)
- Alcohol or drug misuse
- Social isolation and loneliness
Symptoms
- Persistent low mood most of the day, nearly every day
- Loss of interest or pleasure in activities previously enjoyed
- Significant weight change or appetite disturbance
- Sleep problems: too little or too much
- Fatigue and loss of energy
- Feelings of worthlessness or excessive guilt
- Difficulty concentrating or making decisions
- Thoughts of death, self-harm, or suicide
When to see a doctor
If you have seriously harmed yourself, taken an overdose, or feel you may act on suicidal thoughts, call emergency services (999 in the UK) or go to an emergency department now. Ask someone to stay with you and help you get care. For suicidal thoughts without immediate danger, contact your crisis team, an urgent GP service or NHS 111. Samaritans on 116 123 provides listening support in the UK and Ireland; it does not replace emergency medical treatment. Arrange a medical review if low mood persists or affects daily life.
Diagnosis
PHQ-9 questionnaire assesses severity. Clinical interview explores symptoms, their duration, and impact. Blood tests (thyroid, anaemia, calcium) rule out physical causes of low mood.
Treatments
Talking therapies
Cognitive behavioural therapy (CBT) is the most evidence-based psychological treatment. Helps identify and change negative thought patterns. Interpersonal therapy and counselling are also effective.
Antidepressant medication
SSRIs such as sertraline or fluoxetine are first-line medication. They take 2 to 4 weeks to show effect. Taken for at least 6 months after recovery to reduce relapse risk.
Combined treatment
For moderate to severe depression, combining medication with psychological therapy is more effective than either alone. Specialist input for treatment-resistant cases.
Self-care and lifestyle
- Physical exercise is one of the most effective non-drug treatments for mild to moderate depression
- Maintain social connections even when it feels difficult
- Establish a regular sleep routine as poor sleep worsens depression
- Reduce or eliminate alcohol which is a depressant and worsens outcomes
Prevention
No guaranteed prevention, but building strong social connections, managing stress, maintaining healthy lifestyle habits, and seeking early help for symptoms can reduce severity and duration.
Sources for targeted updates
Updated: 11 September 2026. Distinguishing immediate danger from crisis listening support. This update covers the named sections; a full review of the remaining guide is pending.