Health A to Z
Selective serotonin reuptake inhibitors (SSRIs) are a widely used type of antidepressant medication.
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 a number of other mental health conditions, including:
SSRIs can sometimes be used to treat other conditions, such as premature ejaculation, premenstrual syndrome (PMS), fibromyalgia and irritable bowel syndrome (IBS). Occasionally, they may also be prescribed to treat pain.
It's thought that SSRIs work by increasing serotonin levels 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.
SSRIs are usually taken in tablet form. When they're prescribed, you'll 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 that 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.
Read more about SSRI doses.
SSRIs aren't suitable for everyone. They're not usually recommended if you're pregnant, breastfeeding or under 18, because there's an increased risk of serious side effects. However, exceptions can be made if the benefits of treatment are thought to outweigh the risks.
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 medicines you need to avoid.
Read more about the cautions and interactions of SSRIs.
Most people will only experience a few mild side effects when taking SSRIs. These can be troublesome at first, but they'll generally improve with time.
Common side effects of SSRIs can include:
You'll usually need to see your doctor every few weeks when you first start taking SSRIs to discuss how well the medication is working. You can also contact your doctor at any point if you experience any troublesome or persistent side effects.
Read more about the side effects of SSRIs.
Selective serotonin reuptake inhibitors (SSRIs) aren't suitable for everyone. They can cause problems if you have other health conditions or if they're taken alongside other medications.
Some of the issues you and your doctor will need to bear in mind when taking SSRIs, or when considering using them, are described below.
SSRIs may not be suitable if you have any of the following conditions:
SSRIs may need to be used with caution or not at all if you have one of these conditions, because the medication could increase your chance of experiencing serious side effects.
As a precaution, SSRIs aren't usually recommended during pregnancy, particularly during the first three months (the first trimester). This is because there may be a risk to the baby.
However, exceptions can be made if the risk posed by depression (or another mental health condition) outweighs the potential risks of treatment.
Possible risks of taking SSRIs during pregnancy include:
However, it isn't clear whether SSRIs definitely cause these complications. Most experts think that if SSRIs do increase the risks of complications during pregnancy, the increase is probably small.
If you're pregnant and think you may be depressed, you should discuss the risks and benefits of using SSRIs with your doctor. If SSRIs are recommended, you'll usually be prescribed fluoxetine, citalopram or sertraline because these are thought to be relatively safe to use.
You should also speak to your doctor for advice if you become pregnant while you're taking SSRIs.
As a precaution, SSRIs aren't usually recommended if you're breastfeeding. This is because the medication may be passed to your baby in your breast milk.
However, SSRIs may be used if it's thought that the benefits of treatment and benefits of breastfeeding your baby outweigh the potential risks.
If you're prescribed SSRIs when breastfeeding, paroxetine or sertraline are usually recommended.
There are also concerns that the use of SSRIs could affect brain development in children and young people.
However, children and young people under the age of 18 may be offered an SSRI if talking therapies, such as cognitive behavioural therapy (CBT), alone haven't helped. In such cases, an SSRI will only be prescribed in addition to a talking therapy and treatment must be supervised by a psychiatrist (a doctor who specialises in treating mental health conditions).
If an SSRI is recommended, fluoxetine is usually the first choice.
Some SSRIs can cause dizziness, drowsiness and blurred vision, particularly when you first start taking them.
If you experience these problems, you should avoid driving or using heavy tools and machinery.
SSRIs can react unpredictably with certain other medications (known as "interacting"), potentially increasing the risk of side effects such as bleeding or a problem known as "serotonin syndrome".
Read more about the side effects of SSRIs.
Some of the medications that can interact with some SSRIs include:
However, this isn't an exhaustive list of all the medications that can interact with SSRIs, and not all of these interactions apply to all types of SSRI.
You should always make sure you carefully read the patient information leaflet that comes with your SSRI medication to see if there are any medications you should avoid. If in doubt, your pharmacist or GP should be able to advise you.
Alcohol isn't usually recommended if you're taking an SSRI, because it can increase any drowsiness you may experience and can make feelings of depression worse.
The SSRI, fluvoxamine, is also known to enhance the effects of caffeine, so people who drink large amounts of caffeine may experience unpleasant symptoms such as palpitations, feeling sick, restlessness and insomnia.
You should therefore avoid drinking large amounts of caffeinated drinks, such as tea, coffee, energy drinks and cola, while taking fluvoxamine.
St John’s wort is a popular herbal remedy promoted for the treatment of depression.
While there's some evidence that St John's wort may help mild to moderate depression, many experts advise against using it because the amount of active ingredient can vary significantly and you can never be sure what sort of effect it will have on you.
Taking St John's wort alongside SSRIs can also potentially cause serious health problems.
When prescribing selective serotonin reuptake inhibitors (SSRIs), your doctor will usually select the lowest possible dose thought necessary to improve your symptoms.
This approach is intended to reduce the risk of side effects. If the prescribed dose proves ineffective, it can be gradually increased.
SSRIs are usually taken in tablet form. Depending on the type of SSRI prescribed and the severity of your depression, you'll usually have to take one to three tablets a day.
It will usually take two to four weeks before you begin to notice the effects of SSRIs. You'll have regular meetings with your doctor when you first start taking SSRIs and you should let them know if you haven't noticed any improvement after four to six weeks. They may recommend increasing your dose or trying an alternative antidepressant.
It's usually recommended that a course of SSRIs lasts at least six months to prevent your condition recurring when you stop. However, if you've experienced previous episodes of depression, a two-year course may be recommended. Some people with recurring problems are advised to carry on taking medication indefinitely.
It's important not to miss any of your doses, because this could make your treatment less effective.
If you do miss a dose, take it as soon as you remember, unless it's almost time to take your next dose, in which case you should just skip the missed dose. Don't take a double dose to "make up" for the one you missed.
Taking a double dose is unlikely to be harmful, but you should only do so if advised by a medical professional.
You shouldn't suddenly stop taking SSRIs, even if you feel better. Stopping suddenly can lead to withdrawal symptoms such as:
If your GP or mental health specialist decides to stop your course of SSRIs, they'll reduce the dose gradually over a few weeks.
The side effects of selective serotonin reuptake inhibitors (SSRIs) can be troublesome at first, but most improve with time.
In general, SSRIs are better tolerated than most other types of antidepressants. The majority of people will only experience a few mild side effects when taking them.
It's important to persist with treatment, even if you're affected by side effects, as it will take several weeks before you begin to benefit from treatment. With time, you should find that the benefits of treatment outweigh problems related to side effects.
You'll 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 particularly troublesome or persistent side effects.
Some of the main side effects of SSRIs are described below, but this isn't an exhaustive list and some of these won't necessarily apply to the specific SSRI you're taking. For information about the side effects of a particular SSRI, check the information leaflet that comes with your medication.
Common side effects of SSRIs can include:
These side effects should improve over time, although some – such as sexual problems – can persist.
Less common side effects of SSRIs can include:
Speak to your doctor or go to your nearest hospital immediately if you vomit blood, have blood in your stools, or have problems passing urine.
Serotonin syndrome is an uncommon, but potentially serious, set of side effects linked to SSRIs.
Serotonin syndrome occurs when the levels of a chemical in your brain called serotonin become too high. It's usually triggered when you take an SSRI in combination with another medication (or substance) that also raises serotonin levels, such as another antidepressant or St John’s wort.
Symptoms of serotonin syndrome can include:
If you experience the symptoms listed above, you should stop taking the medication and seek immediate advice from your GP or specialist. If this isn't possible, call NHS 111.
Symptoms of severe serotonin syndrome include:
If you or someone you know experience symptoms of severe serotonin syndrome, seek emergency medical help immediately by dialling 999 and asking for an ambulance.
Elderly people who take SSRIs may experience a severe fall in sodium (salt) levels known as hyponatremia. This may lead to a build-up of fluid inside the body's cells, which can be potentially dangerous.
This side effect occurs because SSRIs can block the effects of a hormone that helps to regulate levels of sodium and fluid in the body. Elderly people are vulnerable because fluid levels become more difficult for the body to regulate.
Mild hyponatremia can cause symptoms similar to depression or side effects of SSRIs, such as:
More severe hyponatremia can cause the following symptoms:
The most serious cases of hyponatremia can cause you to stop breathing or go into a coma.
If you suspect that you or someone in your care has mild hyponatremia, call your GP for advice and stop taking SSRIs for the time being. If you suspect severe hyponatremia, call 999 to request an ambulance.
Hyponatremia can be treated by feeding a sodium solution into the body through an intravenous drip.
Contact your GP or go to hospital immediately if you have thoughts of killing or harming yourself at any time while you're taking SSRIs.
It may be useful to tell a relative or close friend that you've started taking antidepressants and ask them to read the leaflet that comes with your medication. Ask them to tell you if they think your symptoms are getting worse, or if they're worried about changes in your behaviour.