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Overview - Antidepressants

Antidepressants are a type of medication. You take them to treat clinical depression or prevent it from recurring.

You can also take them for other conditions, including:

  • obsessive-compulsive disorder (OCD)
  • generalised anxiety disorder
  • post-traumatic stress disorder (PTSD)

Antidepressants are also sometimes used to treat people with long-term (chronic) pain.

How antidepressants work

Antidepressants work by increasing levels of a group of chemicals in the brain. These are neurotransmitters. They may also work by boosting your immune response. This can be suppressed if you have had depression for a long time.

Some neurotransmitters, such as serotonin and noradrenaline, can improve mood and emotion. Although this process isn't fully understood.

Increasing levels of neurotransmitters can also disrupt pain-signals sent by nerves. This may explain why some antidepressants can help relieve long-term pain.

Antidepressants can treat the symptoms of depression. But they don't always address its causes. They're usually used with therapy to treat severe depression or other mental health conditions caused by emotional distress.


Most people benefit from taking antidepressants to some degree. But they may not be as effective as previously thought in cases of mild depression.

But they're the most effective treatment in relieving symptoms quickly. Particularly in cases of severe depression.

50-65% of people treated with an antidepressant for depression will see an improvement.

Doses and duration of treatment

Antidepressants are usually taken in tablet form. You'll start on the lowest possible dose thought necessary to improve your symptoms.

You will need to take them for around 7 days without missing a dose before you feel the benefit. Don't stop taking them if you get some mild side effects early on, as these effects usually wear off quickly.

If you take them for 4 weeks without feeling any benefit, speak to your GP or mental health specialist. They may recommend increasing your dose or trying an alternative medication.

A course of treatment usually lasts for 6 months. You may need to them for 2 years or longer if you have a previous history of depression. If you have recurrent depression may need to take them indefinitely.

Side effects

Different antidepressants can have a range of different side effects. See the patient information leaflet that comes with your medicine for a full list of side effects.

In general, the most common side effects of antidepressants are usually mild. Side effects should improve within a few days or weeks of treatment, as the body gets used to the medication.

Non-urgent advice: Find your patient information leaflet

Your patient information leaflet is the leaflet that comes with your medicine. You can find a digital version of the leaflet online.

Report side effects

You can report any suspected side effects to the the Health Products Regulatory Authority (HPRA): report an issue -

Different types of antidepressants

There are different types of antidepressants. Here are some of the most widely used types.

Selective serotonin reuptake inhibitors (SSRIs)

SSRIs are the most prescribed type of antidepressants. They're usually preferred over other antidepressants, as they cause fewer side effects. An overdose is also less likely to be serious.

Fluoxetine is probably the best-known SSRI (sold under the brand name Prozac). Other SSRIs include citalopram (Cipramil), paroxetine (Seroxat) and sertraline (Lustral).

Serotonin-noradrenaline reuptake inhibitors (SNRIs)

SNRIs are like SSRIs. They are a more effective antidepressant than SSRIs. But the evidence that SNRIs are more effective in treating depression is uncertain. It seems that some people respond better to SSRIs, while others respond better to SNRIs.

Examples of SNRIs include duloxetine (Cymbalta and Yentreve) and venlafaxine (Efexor).

Noradrenaline and specific serotonergic antidepressants (NASSAs)

NASSAs may be effective for some people who are unable to take SSRIs. The side effects of NASSAs are like those of SSRIs, with fewer sexual problems. They may also make you more drowsiness at first.

The main NASSA prescribed in the UK is mirtazapine (Zispin).

Tricyclic antidepressants (TCAs)

TCAs are an older type of antidepressant. They're no longer recommended as a first-line treatment for depression. This is because they can be more dangerous if you take an overdose. They also cause more unpleasant side effects than SSRIs and SNRIs.

You can take them if you have severe depression that does not respond to other treatments. You can also take them for other mental health conditions, such as OCD and bipolar disorder.

Examples of TCAs include amitriptyline (Tryptizol), clomipramine (Anafranil) and imipramine (Tofranil).

You can take some types of TCAs, such as amitriptyline for chronic nerve pain.

Alternatives to antidepressants

Alternative treatments for depression include talking therapies such as cognitive behavioural therapy (CBT).

CBT helps you manage problems by thinking more positively. It frees you from unhelpful patterns of behaviour.

Moderate to severe depression is generally treated with antidepressants and CBT.

Antidepressants work quickly in reducing symptoms. CBT takes time to deal with the causes of depression and ways of overcoming it.

150 minutes per week of moderately vigorous exercise are recommended for adults to maintain physical and mental wellbeing. For example, fast walking, swimming or running.

Content supplied by the NHS and adapted for Ireland by the HSE

Page last reviewed: 20 August 2022
Next review due: 20 August 2025

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.