No single cause
The NHS is clear that there is no single cause of depression. It can happen for many reasons and has many different triggers.
For most people, several things add up. A difficult event might land at a time when someone is already tired, isolated, unwell or under financial strain. Sometimes there is no obvious trigger at all, which can be confusing. Depression can affect people whose lives look fine from the outside.
Understanding possible causes is useful, but it is not about blame. Whatever led to it, depression is a health condition that deserves care and treatment.
Stressful life events
Stressful or upsetting events are one of the most common triggers. The NHS lists examples such as bereavement, divorce, illness, redundancy, and job or money worries. Mind adds relationship breakdown, losing a job and bullying.
Sometimes the effect is delayed. People often cope during a crisis and only feel the full weight of it weeks or months later, when things have settled down.
Difficult experiences in childhood, such as abuse, neglect or losing a parent, can also make people more vulnerable to depression later in life, according to Mind.
Grief is a natural response to loss, and it is not the same as depression. But grief can sometimes develop into depression. What is depression? explains the difference.
Biology and the brain
Depression involves changes in how the brain works, including the systems that regulate mood, sleep, appetite, energy and motivation. Scientists are still learning exactly how these changes happen.
You may have heard that depression is caused by a “chemical imbalance”. This is an oversimplification. Brain chemistry plays a part, but it works alongside life experience, stress, physical health and thinking patterns. Antidepressants can help many people, but that does not mean depression is only about chemistry. See antidepressants for how they are used.
Hormonal changes can also play a part. The NHS notes that pregnancy and giving birth, and menopause, particularly the first few years, can trigger depression in some people.
Genetics and family history
Depression can run in families. The NHS says that if a close family member such as a parent, brother or sister has had depression, you are more likely to develop it too.
This does not mean depression is inevitable. Mind notes that no single “depression gene” has been found. Family history is one risk factor among many, and families also share environments, habits and experiences.
It is still worth telling your GP about any family history of depression, bipolar disorder or other mental health conditions. It can help with diagnosis and treatment choices.
Personality and thinking styles
Some personality traits can make people more vulnerable. The NHS gives the examples of low self-esteem and being overly self-critical. Mind also mentions patterns such as blaming yourself and getting stuck in negative thinking.
These patterns can be learned, and they can also be changed. Talking therapies such as cognitive behavioural therapy (CBT) focus on exactly this. Treatment for depression describes the options.
Physical illness
Living with a long-term or serious physical illness raises the risk of depression. This may be because of pain, disability, loss of independence, worry about the future, or the illness itself affecting the brain and body.
The NHS mentions conditions such as head injuries and an underactive thyroid (hypothyroidism). Mind lists chronic pain, life-threatening illnesses and hormone problems, including thyroid problems.
Some physical conditions cause symptoms that look like depression, such as tiredness and low energy. This is one reason why a GP may suggest blood tests. Getting diagnosed explains more.
Medicines
Some prescribed medicines can affect mood as a side effect, according to Mind. If your mood dropped after starting a new medicine or changing a dose, mention it to your GP or pharmacist.
Do not stop a prescribed medicine on your own, even if you think it may be affecting your mood. Stopping suddenly can cause other problems. A GP or pharmacist can look at your medicines and discuss alternatives safely.
Alcohol and drugs
Many people drink alcohol or use drugs to cope with feelings of low mood. It can bring brief relief, but the NHS warns it can lead to a spiral of depression.
Alcohol is a depressant. It can disturb sleep, make anxiety worse the next day and affect relationships, work and money, all of which can deepen low mood. The NHS also notes a strong link between cannabis use and mental illness.
If you are worried about how much you are drinking or using, it is worth raising with your GP. It is common, and help is available without judgement.
Loneliness
Feeling cut off from other people is linked with depression. The NHS lists loneliness, such as being cut off from family and friends, as something that can increase the risk.
It works both ways. Loneliness can trigger low mood, and depression can make people withdraw, which increases loneliness. NHS Every Mind Matters suggests small steps such as regular chats with friends or family, joining a group, volunteering, and talking openly about how loneliness affects you. Self-help for depression has more ideas.
Lifestyle factors
Mind notes that poor sleep, a poor diet and lack of physical activity can make people more vulnerable, although they are rarely the whole cause on their own. Improving them can support recovery alongside other treatment.
Why causes still matter for treatment
Finding out what may have contributed can shape treatment. NICE recommends that when depression has not responded to treatment, clinicians look at personal, social and environmental factors, and at physical or other mental health conditions, that might explain why.
For example, untreated thyroid problems, heavy drinking, ongoing money worries or a separate condition such as anxiety can all hold back recovery. Tackling these can make treatment work better.