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This factsheet is also available as a pdf.

Antidepressants are types of medication used to treat clinical depression. However, the name is also somewhat misleading, as many antidepressants are also prescribed for a range of other disorders. These include other mental health problems such as anxiety, obsessive-compulsive and post-traumatic stress disorders; they may also be used to treat conditions like long-term pain.

How do they work?

  • It is not fully clear how antidepressants produce their effects as we still do not fully understand depression, but it is thought that it is due at least in part, to increasing levels of neurotransmitters such as serotonin and noradrenaline. Such neurotransmitters have a role in improving mood and protecting against stress, though as with many aspects of neuroscience this is not completely understood.

Different types of antidepressants

  • There are a number of different types of antidepressant drugs of which the newer selective serotonin reuptake inhibitors (SSRIs e.g. fluoxetine, sertraline, paroxetine, citalopram) are the most commonly used and are generally the first choice for treatment for the conditions listed above. Newer antidepressants are used because they have better tolerated side effects and are safer in overdose than the old ones (see below); however effectiveness of both is similar.
  • Other antidepressants include serotonin-noradrenaline reuptake inhibitors (SNRIs e.g. venlafaxine & duloxetine), noradrenaline and specific serotonergic antidepressants (NASSAs) and tricyclic antidepressants (TCAs). TCAs are often reserved for use in cases of severe depression or OCD, and aren’t used as a first-line treatment because they are associated with more unpleasant side effects and a greater risk of overdose.

What are the side effects?

  • Side effects can vary between the different classes but can include nausea, loss of appetite or sexual dysfunction with SSRIs, and drowsiness or weight gain with TCAs.
  • There has been research suggesting an association between use of antidepressants and increased risk of suicidal behaviour, however, many more studies suggest that the risk is much less than is the risk for suicide in cases of untreated depression. Experts agree that there is a need for careful monitoring in the first few weeks of treatment when the risk is highest.
  • Depression in pregnancy and following childbirth can potentially have serious consequences; suicide is a leading cause of maternal death in the UK. Recent research suggests that whilst the absolute risk of birth defects remains very low, there is an increased risk following the use of anti-depressants during the first three months of pregnancy. There is debate about whether the defects are caused by the medication, or the illness itself. RCOG states that their advice for pregnant women suffering with depression is that the benefits of using antidepressants generally outweigh the risks, however all pros and cons should be discussed with a clinician.


How effective are they?

  • Most antidepressants won’t work immediately but their effects can be felt after around one or two weeks though this is variable. The lowest possible dose is usually prescribed to reduce the risk of side effects. If only minimal benefit is felt after one month then an increase in dose may be recommended, and if no benefit is seen then a change in medication may be recommended. A course will typically last for at least six months.
  • Estimates of effectiveness suggest 50-65% of patients treated for depression with an antidepressant benefit compared with around half that figure for people who are treated with a placebo.
  • Many organisations suggest that the prescription of antidepressants should be avoided in children below the age of 12 as efficacy is lower in this group. It is recommended that people under the age of 18 receive psychotherapy first, though a specific antidepressant (fluoxetine/Prozac) may be used as a first option in non-responsive cases or cases of moderate/severe depression (Sertraline/Citalopram as a second option).

How commonly are they prescribed?

  • Antidepressants are usually a first line of treatment in adults with moderate to severe depression and the first line treatment given to people with anxiety disorders.
  • Antidepressant prescription is common and may be increasing. There is a lot of interest in both possible over – and under – prescribing of antidepressants.
  • A recent report stated that the prescription of antidepressant drugs in England saw a significant rise between 1998 and 2012.
  • A report from the US-based Centers for Disease Control and Prevention (CDC) put the proportion of Americans taking antidepressants at 11%. [need to source UK data]
  • Coupled with this, access to specialist knowledge and care is not always well integrated with primary care which can further lead to misdiagnosis or wrongful prescription.
  • A common perception is that patients should stop taking antidepressants as soon as possible, but for some patients (particularly those who have recurrent episodes) they may need to consistently take the drugs over the long term (i.e. years) to prevent relapses. There is good evidence that antidepressants should be taken for a full 6 months after recovery for first episodes of depression and longer after recurrent episodes.

What other treatments are available?

  • The National Institute for Health and Care Excellence recommends that antidepressants do not form the sole treatment except in the cases of moderate/severe depression.
  • Other treatments which may be used instead of, or as well as, antidepressants include talking therapies such as cognitive behavioural therapy (CBT).

The SMC also produced a Factsheet on depression.


Sources / further information

CDC antidepressant use brief

HeadMeds – young people and mental health medication

Mind antidepressants page

NHS Choices antidepressants introduction

NHS Choices – side effects of antidepressants

NHS Choices – when antidepressants are used

NICE Antidepressant treatment in adults pathway

NICE Depression in adults: recognition and management

Nuffield Trust focus on: antidepressant prescribing

Royal College of Psychiatrists antidepressants page

World Health Organization depression fact sheet

Bérard, A. et al. (2016) “The risk of major cardiac malformations associated with paroxetine use during the first trimester of pregnancy: a systematic review and meta-analysis.” BJCP Vol 81, Iss 4 p589–604

Gibbons, R. et al. (2012) “Suicidal thoughts and behaviour with antidepressant treatment: reanalysis of the randomized placebo-controlled studies of fluoxetine and venlafaxine.” Arch Gen Psychiatry 69(6):580-7

Sharma, T. et al. (2016) “Suicidality and aggression during antidepressant treatment: systematic review and meta-analyses based on clinical study reports.” BMJ 352:i65.

Stone, M. et al. (2009) “Risk of suicidality in clinical trials of antidepressants in adults: analysis of proprietary data submitted to US Food and Drug Administration.” BMJ 339:b2880

This is a Factsheet issued by the Science Media Centre to provide background information on science topics relevant to breaking news stories. This is not intended as the ‘last word’ on a subject, but rather a summary of the basics and a pointer towards sources of more detailed information. These can be read as supplements to our Roundups and/or briefings.


For more information about our Factsheets please contact the Science Media Centre on 020 7611 8300 or email


Updated 25/07/2017

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