Depression: symptoms, causes, treatment and how long it lasts

The NHS says the symptoms of depression can be complex and vary widely between people, and that you are unlikely to have all of the symptoms listed. They persist for weeks or months and are bad enough to interfere with your work, social life and family life. Depression can come on gradually, so it can be hard to notice that something is wrong, and it can sometimes take a friend or family member to suggest it.

The NHS says most people go through periods of feeling down, but when you are depressed you feel persistently sad for weeks or months rather than just a few days. It describes depression as a real illness with real symptoms, and says it is not a sign of weakness or something you can get over by pulling yourself together.

Symptoms range from mild to severe. At its mildest you may simply feel persistently low in spirit, while severe depression can make you feel suicidal, or that life is no longer worth living. The NHS adds that many people with depression also have symptoms of anxiety.

Doctors describe depression in adults as either less severe (mild) or more severe (moderate or severe), based on the symptoms, how long it lasts and the impact on your daily life. A few people with severe depression may have symptoms of psychosis. You will usually be asked to answer a set of questions to help doctors judge how severe it is.

The NHS says treatment usually involves a combination of self-help, talking therapies and medicines, and that the treatment recommended is based on the type and severity of depression.

The NHS says a GP can refer you for talking therapies, or you can refer yourself directly to an NHS talking therapies service without a GP referral. Waiting times can be several weeks or months, and a GP can tell you how long you might wait and what to do if you get worse or need support in the meantime.

The NHS describes several types. Cognitive behavioural therapy (CBT) helps you understand your thoughts and behaviour and usually involves 8 to 16 sessions. Interpersonal therapy focuses on relationships and usually involves 8 to 16 sessions. Behavioural activation looks at links between activities and mood and usually involves 12 to 16 sessions. Counselling may be offered as 8 to 16 sessions. Individual problem-solving (6 to 12 sessions) is only recommended for more severe depression, and behavioural couples therapy (15 to 20 sessions over 5 to 6 months) may be offered if relationship problems could be contributing.

The NHS says most people with moderate or severe depression benefit from antidepressants, but not everybody does. You may respond to one and not another, and may need to try two or more before you find one that works. The different types work about as well as each other, but side effects vary.

When you start, the NHS says you should see a GP or specialist nurse every week or 2 for at least 4 weeks to check how well they are working. Symptoms should start to improve within 4 weeks. If they are working, you will need to continue at the same dose for at least 4 to 6 months after your symptoms have eased. If you have had episodes of depression in the past you may need to continue long term, and you will be reviewed at least twice a year.

The NHS says antidepressants are not addictive, but you may get withdrawal symptoms if you stop suddenly or miss a dose, so you will be advised to reduce the dose gradually. Contact a GP straight away if feelings of hopelessness or suicidal thoughts start or get worse after starting antidepressants.

The NHS says there is no single cause of depression. It can occur for a variety of reasons and has many triggers, and different causes can combine. Examples it gives include an upsetting or stressful life event such as bereavement, divorce, illness, redundancy or money worries.

• Family history: if a parent, sister or brother has had depression you are more likely to develop it, though it does not mean you definitely will.

• Personality: traits such as low self-esteem or being overly self-critical may make you more vulnerable.

• Pregnancy and giving birth: hormonal and physical changes and added responsibility can lead to postnatal depression.

• Menopause: it can sometimes trigger depression, particularly in the first few years.

• Loneliness, and alcohol or drugs: alcohol affects the chemistry of the brain and increases the risk of depression, and cannabis may bring it on, particularly in teenagers.

• Illness: a longstanding or life-threatening illness, long-term pain, a severe head injury, or in some people an underactive thyroid.

The NHS says you can get depression when you are pregnant, and that it is called antenatal depression. Some mood changes, such as feeling tired or irritable, are normal in pregnancy, but if you often feel low and hopeless and no longer enjoy things you used to, it says to talk to a midwife or GP. If it is not treated, symptoms can get worse and may continue after the baby is born as postnatal depression.

Treatment can include self-help, a self-help course or NHS talking therapies, and sometimes antidepressants. The NHS says antidepressants may be recommended for moderate or severe depression if you do not want psychological therapy, it has not worked, or you prefer medicine. It advises talking to a GP or the doctor in charge of your care about antidepressants that are safer to take in pregnancy, as they will usually offer the type with the lowest risk for you and your baby.

Contact a GP immediately if you start hearing or seeing things that are not real, or develop strong beliefs not shared by others. Call 999 if you think there is a danger that you might harm yourself or others.

The NHS says there are no physical tests for depression, but a GP may examine you and carry out some urine or blood tests to rule out other conditions with similar symptoms, such as an underactive thyroid. The main way a GP tells whether you have depression is by asking questions about your general health and how the way you are feeling affects your daily life.

They will also ask about your medical history, previous mental health problems, home environment and lifestyle, and any recent triggers. They will ask whether you have had thoughts of suicide or self-harm, and may use a questionnaire to assess your symptoms. The NHS says any discussion with a GP is confidential, and that this will only be broken if there is a significant risk of harm to you or others.

The NHS does not give a single length of time. It says depression can come on gradually and that symptoms persist for weeks or months, and that a low mood can improve after a short period without being depression. It also says that the sooner you see a doctor, the sooner you can be on the way to recovery.

With treatment, the NHS says antidepressant symptoms should start to improve within 4 weeks, and that you will need to continue the medicine for at least 4 to 6 months after your symptoms ease. If you have had depression before, you may need to take antidepressants long term. The NHS says that with the right treatment and support, most people can make a full recovery.

The NHS lists several conditions in which depression is the main problem or one of the symptoms. It also says grief and depression can be hard to tell apart: grief is a natural response to a loss, while depression is an illness, and people who are grieving may have symptoms of depression that usually improve with time.

The NHS pages on depression in adults point out that depression in children and young people is covered separately. One difference it states is about medicines: SSRIs may not be prescribed for people under 18 because research shows the risk of self-harm and suicidal behaviour may increase, and fluoxetine is the only SSRI that can be prescribed for under-18s, and only when a specialist has given the go-ahead.

If you are worried about a child or teenager, the NHS advice for adults applies as a starting point: see a GP, who can refer to the right service.

The NHS says to get advice from 111 or ask for an urgent GP appointment if you need urgent help for your mental health. You can get help from 111 online or call 111 and select the mental health option, and 111 will tell you the right place to get help.

Call 999 or go to A&E now if someone's life is at risk, for example they have seriously injured themselves or taken an overdose, or you do not feel you can keep yourself or someone else safe. The NHS says a mental health emergency should be taken as seriously as a physical one and you will not be wasting anyone's time.

The NHS also lists free listening services such as Samaritans, which offer confidential support from trained volunteers, and Childline for people under 19. Contact a GP straight away if you have feelings of hopelessness or suicidal thoughts that start or get worse after starting antidepressants.

On the NHS, depression is usually assessed by a GP, with referral to NHS talking therapies (which you can also self-refer to), and to a community mental health team if depression is severe. Medicines are prescribed by a GP or specialist.

Private psychiatrists, psychologists and therapists also see people with depression. The assessment, the evidence-based therapies and the main antidepressant options are broadly the same; the main differences are how quickly you can be seen and who pays. It is sensible to check a therapist's professional registration and to keep your GP informed about any medicines you are prescribed.