Selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are a widely used type of antidepressant medication.

They are mainly prescribed to treat depression, particularly persistent or severe cases, and are often used in combination with a talking therapy such as cognitive behavioural therapy (CBT).

SSRIs are usually the first choice medication for depression because they generally have fewer side effects than most other types of antidepressant.

As well as depression, SSRIs can be used to treat certain other mental health conditions, including:

generalised anxiety disorder (GAD)
obsessive compulsive disorder (OCD)
panic disorder
severe phobias, such as agoraphobia and social phobia
bulimia
post-traumatic stress disorder (PTSD)

SSRIs can also be used to treat people with certain other conditions, such as premature ejaculation, premenstrual syndrome (PMS), fibromyalgia and irritable bowel syndrome (IBS).

How they work

It's thought that SSRIs work by increasing the levels of a chemical called serotonin in the brain.

Serotonin is a neurotransmitter (a messenger chemical that carries signals between nerve cells in the brain). It's thought to have a good influence on mood, emotion and sleep.

After carrying a message, serotonin is usually reabsorbed by the nerve cells (known as 'reuptake'). SSRIs work by blocking ('inhibiting') reuptake, meaning more serotonin is available to pass further messages between nearby nerve cells.

It would be too simplistic to say that depression and related mental health conditions are caused by low serotonin levels, but a rise in serotonin levels can improve symptoms and make people more responsive to other types of treatment, such as CBT.

Doses and duration of treatment

SSRIs are usually taken in tablet form. When they are prescribed, you will start on the lowest possible dose thought necessary to improve your symptoms.

SSRIs usually need to be taken for two to four weeks before the benefit is felt. You may experience mild side effects early on, but it's important you don't stop taking the medication. These effects will usually wear off quickly.

If you take an SSRI for four to six weeks without feeling any benefit, speak to your GP or mental health specialist. They may recommend increasing your dose or trying an alternative antidepressant.

A course of treatment usually lasts for at least six months, although longer courses are sometimes recommended and some people with recurrent problems may be advised to take them indefinitely.

Things to consider

SSRIs are not suitable for everyone. They are not usually recommended if you are pregnant, breastfeeding or under 18 because there is an increased risk of serious side effects, although exceptions can be made if the benefits of treatment are thought to outweigh the risks.

SSRIs also need to be used with caution if you have certain underlying health problems, including diabetes, epilepsy and kidney disease.

Some SSRIs can react unpredictably with other medicines, including some over the counter painkillers and herbal remedies such as St John’s wort. Always read the information leaflet that comes with your SSRI medication to check if there are any medications you need to avoid.

Read more about the cautions and interactions of SSRIs.

Side effects

Most people will only experience a few mild side effects when taking SSRIs. These can be troublesome at first, but most will generally improve with time.

Common side effects of SSRIs can include:

feeling agitated, shaky or anxious
feeling or being sick
dizziness
blurred vision
low sex drive
difficulty achieving orgasm during sex or masturbation
in men, difficulty obtaining or maintaining an erection (erectile dysfunction)

You will usually see your doctor every few weeks when you first start taking SSRIs, to discuss how well the medication is working. However, you can contact your doctor at any point if you experience any troublesome or persistent side effects.

Read more about the side effects of SSRIs.