Selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are a type of medicine used to treat depression.

Information written and reviewed by Certified Doctors.

Contents

Introduction

Selective serotonin reuptake inhibitors (SSRIs) are a type of medicine used to treat depression.

SSRIs can also be used to treat other conditions, such as:

Read more about the uses of selective serotonin reuptake inhibitors.

How they work

SSRIs boost levels of a substance called serotonin in the brain. When serotonin is released it helps lift mood.

It is thought people with depression release only small amounts of serotonin. The SSRIs prevent the nerve cells in the brain absorbing serotonin.

Depression is not simply caused by serotonin levels. But a rise in serotonin levels can improve mood and make people more responsive to other types of treatment, such as the talking therapy cognitive behavioural therapy.

Read more about how selective serotonin reuptake inhibitors work.

Side effects

Common side effects of SSRIs include:

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

Most people find that side effects improve with time as their body gets used to the effects of the medication.

Some people experience suicidal thoughts and a desire to self-harm when they first start taking SSRIs. Those under 25 years of age seem particularly at risk.

Contact your doctor, or go to hospital immediately, if you have thoughts of killing or harming yourself at any time while you are taking antidepressants.

Read more about the side effects of selective serotonin reuptake inhibitors.

Dosage

Your doctor will usually prescribe the lowest possible dose to reduce your risk of experiencing side effects. The dose can be gradually increased if it's not enough.

It can take two to four weeks for an SSRI to start improving your mood.

You should continue taking your SSRI even if it does not seem to work at first. Sometimes, the symptoms of a condition get worse before the SSRI has started working.

Depending on your previous medical history it may be recommended that you continue to take an SSRI for several months to prevent the condition returning.

Never suddenly stop taking an SSRI as this can lead to unpleasant withdrawal effects such as feeling anxious and dizziness. When it's time for your treatment to end, your dosage will be gradually reduced.

Read more about the dosage of selective serotonin reuptake inhibitors.

Things to consider

SSRIs are not usually recommended in children and should only be given to pregnant women if it is thought benefits of treatment outweigh potential risks.

SSRIs may also not be suitable for people with certain health conditions such as glaucoma (increased pressure in the eye) and kidney problems.

Read more about the cautions associated with selective serotonin reuptake inhibitors.

Some SSRIs can react unpredictably with other medicines, including over-the-counter painkillers and herbal remedies such as St John’s wort.

Always read the information leaflet that comes with your medication to be aware of any potential interactions.

It's usually recommended that you avoid drinking alcohol while taking an SSRI. Alcohol can make SSRIs less effective and make side effects more severe.

Read more about possible interactions with selective serotonin reuptake inhibitors.

Cautions

Selective serotonin reuptake inhibitors (SSRIs) can react unpredictably with other medicines, including over-the-counter medications such as ibuprofen.

Always read the patient information leaflet that comes with your medication to see other medicines you should avoid.

If in doubt your pharmacist or doctor will be able to advise you.

Medical conditions

SSRIs may not be suitable for you if have the following conditions:

  • mania – an extremely excitable mood, sometimes with hallucinations
  • bipolar disorder (alternating bouts of depression and mania) and you are in a manic phase
  • a bleeding disorder, or you are taking medicines that make it more likely that you may bleed, for example warfarin
  • diabetes – both type 1 and type 2 diabetes
  • narrow angle glaucoma – increased pressure in the eye
  • severe kidney disease

Pregnancy

As a precaution, the use of SSRIs is usually not recommended for most pregnant women, especially during the first three months of a pregnancy (the first trimester).

However, exceptions can be made if risks posed by depression (or other mental health conditions) outweigh any potential risks of treatment.

Complications linked to taking SSRIs during pregnancy include:

  • loss of pregnancy
  • birth defects affecting the baby’s heart (congenital heart disease)
  • the baby is born with a rare condition called pulmonary hypertension

However, there is no hard evidence that SSRIs can cause these types of complications.

Most experts think if SSRIs do increase risks of complications in pregnancy then the increase in risk is probably small.

If you are pregnant and are currently depressed you should discuss the pros and cons of treatment with SSRIs with your doctor.

If SSRIs are recommended they will usually be fluoxetine, citalopram or sertraline( as these are thought to be relatively safe to use.

Breastfeeding

Again, as a precaution SSRIs are not usually recommended if you are breastfeeding.

But there are circumstances when both benefits of treatment for depression (or other mental health conditions) and benefits of breastfeeding to your baby outweigh the potential risks.

If you are treated with antidepressants when breastfeeding then paroxetine or sertraline are normally recommended.

Children and young people

SSRIs are not usually recommended in children and young people under the age of 18.

This is because there is evidence they can trigger thoughts about suicide and acts of self-harm in this age group.

Concerns have also been raised that use of SSRIs could affect brain development in children and young people.

An exception can usually only be made if the following points are met:

  • the person being treated has failed to respond to talking therapies such as cognitive behavioural therapy, and
  • the person being treated will continue to receive talking therapies in combination with SSRIs, and
  • the treatment is supervised by a psychiatrist (a doctor who specialises in treating mental health conditions)

If an SSRI is recommended then fluoxetine is usually the first choice.

Alcohol

Alcohol is not usually recommended if you are taking an SSRI as it could make the medication less effective and side effects worse.

Dizziness

Some SSRIs may cause you to feel dizzy, particularly when you first start taking them.

If you do experience dizziness avoid driving and using tools and machinery.

Other antidepressants

You should never take two different types of antidepressants, such as an SSRI and a tricyclic antidepressant (TCA), unless advised by your doctor. This is because certain combinations of antidepressants can make you feel very ill.

If a decision is taken to switch you from one type to another, you will normally gradually reduce the dosage of the first antidepressant before switching to the second.

St John’s wort

St John’s wort is a popular herbal remedy promoted for the treatment of depression.

While there is evidence of its effectiveness many experts advise against using it. This is because the amount of active ingredient varies between individual brands and batches, so you can never be sure what sort of effect it will have on you.

Taking St John's wort with other medications, such as anticonvulsants, anticoagulants, SSRIs and the contraceptive pill, can also cause serious health problems.

You shouldn't take St John's wort if you are pregnant or breastfeeding, as it is unclear whether it is safe.

How they work

Selective serotonin reuptake inhibitors (SSRIs) change the levels of a chemical called serotonin in the brain.

Serotonin is what is known as a neurotransmitter. These are ‘messenger chemicals’ that carry signals between brain cells. Serotonin is thought to have a good influence on mood, emotion and sleep.

After delivering a ‘message’ serotonin is absorbed back into the brain. This is called ‘reuptake’. SSRIs work by blocking reuptake so levels of serotonin in the brain rise over time.

Increasing the levels of serotonin is a gradual process, so most people will need to take SSRIs for two to four weeks before they notice any improvement in their symptoms.

The underlying cause

Conditions such as depression or obsessive compulsive disorder are often complex and can be influenced by a wide range of factors. While SSRIs treat the symptoms of depression they do not necessarily address its cause.

This is why SSRIs are usually used in combination with therapy to treat more complex mental health conditions. The improvement in mood linked to SSRI-use can make a person more receptive to the benefits of therapy.

Interactions with other medicines

When two or more medicines are taken at the same time, the effects of one of the medicines may alter the other.

This is known as a drug–drug interaction. Selective serotonin reuptake inhibitors (SSRIs) can interact with other medicines.

Some of the more common interactions are listed below. However, this is not a complete list.

If you want to check your medicines are safe to take with SSRIs, check our [medicines information] pages for details of all interactions with SSRIs, including alcohol.

Antiplatelets

Antiplatelets are a type of medication used to prevent blood clots.

There is an increased risk of bleeding when SSRIs are taken with antiplatelets such as low-dose aspirin or clopidogrel. Speak to your doctor for advice before taking SSRIs if you take antiplatelets.

Clozapine

Clozapine is a type of medication used to treat schizophrenia and psychosis.

SSRIs can increase the level of clozapine in the blood, which increases the risk of side effects from clozapine. Speak to your doctor for advice before taking SSRIs if you take clozapine.

Duloxetine

Duloxetine is used to treat a number of mood disorders as well as some cases of nerve pain.

There is an increased risk of serotonin syndrome when SSRIs are taken with duloxetine. SSRIs should not be taken with duloxetine.

Lithium

Lithium is used to treat severe depression as well as bipolar disorder.

SSRIs can increase the blood level of lithium, which increases the risk of side effects from lithium.

You should have regular blood tests to monitor the level of lithium in your body, especially when starting or stopping an SSRI or when changing the dose of an SSRI.

Monoamine oxidase inhibitor antidepressants

There is an increased risk of serotonin syndrome when SSRIs are taken with monoamine oxidase inhibitor (MAOI) antidepressants such as isocarboxazid, moclobemide, phenelzine or tranylcypromine.

SSRIs should not be taken with an MAOI antidepressant or for two weeks after stopping an MAOI antidepressant.

Medicines for diabetes

SSRIs may worsen the control of diabetes, which may mean your dose of medicines for diabetes needs to be adjusted. These medicines include gliclazide, glipizide and metformin.

Non-steroidal anti-inflammatory drugs (NSAIDs)

There is an increased risk of bleeding when SSRIs are taken with non-steroidal anti-inflammatory drugs (NSAIDs). These are a type of painkiller that includes ibuprofen, diclofenac or naproxen. Speak to your doctor for advice before taking SSRIs if you take NSAIDs.

Pimozide

Pimozide is a type of medication used to treat schizophrenia and psychosis.

SSRIs increase the level of pimozide in the blood, which increases your risk of side effects from pimozide. SSRIs should not be taken with pimozide.

Rasagiline and selegiline

Rasagiline and selegiline are two medications used in the treatment of Parkinson’s disease.

There is an increased risk of serotonin syndrome when certain SSRIs are taken with rasagiline or selegiline.

Because of this, SSRIs should not be taken with rasagiline or selegiline and SSRIs should not be started for two weeks after stopping rasagiline or selegiline.

Also, selegiline should not be started for five weeks after stopping fluoxetine, two weeks after stopping sertraline and one week after stopping other SSRIs.

Rasagiline should not be started for five weeks after stopping fluoxetine or two weeks after stopping fluvoxamine.

St John's wort

There is an increased risk of serotonin syndrome when SSRIs are taken with the herbal remedy St John's wort. SSRIs should not be taken with St John's wort.

Tramadol

There is an increased risk of seizures (fits) and serotonin syndrome when SSRIs are taken with the painkiller tramadol. Speak to your doctor for advice before taking SSRIs if you take tramadol.

Tricyclic antidepressants

SSRIs can increase the levels of some tricyclic antidepressants (including amitriptyline, clomipramine, dosulepin, imipramine or nortriptyline) in the blood. This increases the risk of side effects from tricyclic antidepressants.

You should only take an SSRI with a tricyclic antidepressant if it is recommended by a specialist in mental health and you are monitored closely for side effects.

Triptans for migraine

There is an increased risk of serotonin syndrome when SSRIs are taken with a triptan such as almotriptan, eletriptan, frovatriptan, naratriptan, rizatriptan, sumatriptan or zolmitriptan. Speak to your doctor for advice before taking SSRIs if you take triptans for migraine.

Tryptophan

Tryptophan is a medication used to treat depression and anxiety disorders.

There is an increased risk of agitation and feeling sick when SSRIs are taken with tryptophan. Speak to your doctor for advice before taking SSRIs if you take tryptophan.

Warfarin

SSRIs can enhance the effect of warfarin, which may increase your risk of bleeding. You should have regular blood tests to monitor the effect on the warfarin, especially when starting or stopping an SSRI or when changing the dose of an SSRI.

Missed and extra doses

When prescribing selective serotonin reuptake inhibitors (SSRIs), your doctor will usually select the lowest possible dose thought needed to improve your symptoms.

This is to reduce your risk of experiencing side effects. If this dose proves ineffective, the dosage can be gradually increased.

SSRIs are usually taken in tablet form. Depending on the type of SSRIs prescribed and the severity of your depression, you will usually take one to three tablets a day.

If you forget to take your tablets on a certain day, don't take an extra dose the next day to ‘make up’ your dose. Instead, carry on taking your tablets as usual.

If you take more tablets than you should, contact your doctor as soon as possible for advice. If you cannot reach your doctor, contact your local out of hours service.

It will probably take two to four weeks before you begin to notice effects of the SSRIs. It is important not to miss a dose as this could make your treatment less effective.

It is usually recommended that a course of SSRIs lasts at least six months. However, if you have experienced previous episodes of depression or other mental health conditions, a two-year course of SSRIs may be recommended.

You should not suddenly stop taking SSRIs prescribed for you, even if you feel better.

If your doctor decides to stop your course of antidepressants, they will reduce the dose gradually, over time.

Side-effects

The side effects of selective serotonin reuptake inhibitors (SSRIs) can be troublesome at first but generally improve with time.

It is important to persist with treatment, even if you are affected by side effects, as it will take several weeks before you begin to benefit from treatment.

With time you should find the benefits of treatment outweigh problems related to side effects.

Common side effects

Common side effects of SSRIs, affecting around one in 10 people include:

  • feeling sick
  • low sex drive
  • difficulty achieving orgasm during sex or masturbation
  • in men, difficulty obtaining or maintaining an erection (erectile dysfunction)
  • blurred vision
  • diarrhoea or constipation
  • dizziness
  • dry mouth
  • feeling agitated or shaky
  • not sleeping well (insomnia) or, alternatively, feeling very sleepy
  • loss of appetite
  • excessive sweating
  • yawning

These side effects should improve over time, although some can occasionally persist.

Less common side effects

Up to one person in 100 may experience the following:

  • bruising or bleeding, including vomiting blood or blood in your stools (speak to your doctor or go to hospital straight away)
  • confusion
  • problems with movement, stiffness, shaking or abnormal movements of the mouth
  • hallucinations (seeing or hearing things that are not real)
  • being unable to pass urine (speak to your doctor or go to hospital straight away)
  • being sick
  • weight gain

Serotonin syndrome

Serotonin syndrome is an uncommon, but potentially serious, set of side effects linked to SSRIs.

Serotonin syndrome occurs when levels of serotonin in your brain become too high. It is 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 include:

  • confusion
  • agitation
  • muscle twitching
  • sweating
  • shivering
  • diarrhoea

You should stop taking the medication and seek immediate advice from your doctor if you experience these symptoms. If this is not possible, call your out of hours service.

Symptoms of severe serotonin syndrome include:

  • a very high temperature (fever) of 39.4°C (103°F) or above
  • seizures (fits)
  • irregular heartbeat (arrhythmia)
  • unconsciousness

Hyponatraemia

A drop in levels of sodium (salt) is a side effect that occurs in elderly people. This is known as hyponatraemia. It leads to a build-up of fluid inside the cells of the body, which can be potentially dangerous.

Mild hyponatraemia can cause the following symptoms:

  • feeling sick
  • headache
  • muscle pain
  • reduced appetite
  • confusion

Severe hyponatraemia can cause the following:

  • feeling listless and tired
  • disorientation
  • agitation
  • psychosis (being unable to tell the difference between reality and your imagination)
  • seizures (fits)

In the most serious cases it can cause:

  • coma
  • stopping breathing

If you suspect that you (or someone in your care) has mild hyponatraemia, call your doctor for advice.

If you suspect severe hyponatraemia, call for an ambulance.

If it is thought you may be at risk your sodium levels may be measured before you begin taking SSRIs and then for a number of weeks afterwards (most cases of SSRI-related hyponatraemia occur in the first weeks of treatment). Sodium levels can be measured using a blood test.

Antidepressants and suicide risk

Some people have experienced suicidal thoughts and a desire to self-harm when they start taking SSRIs. Those under 25 years of age seem particularly at risk.

Contact your doctor, or go to hospital immediately, if you have thoughts of killing or harming yourself at any time while taking SSRIs (or other antidepressants).

It may be useful to tell a relative or close friend you have started taking antidepressants and ask them to read the leaflet that comes with your medication. You should then ask them to tell you if they think your symptoms are getting worse, or if they are worried about changes in your behaviour.

Uses

The main use for selective serotonin reuptake inhibitors (SSRIs) is treating depression.

SSRIs are usually recommended as a first line treatment for moderate to severe depression, when used in combination with a talking therapy such as cognitive behavioural therapy (CBT).

SSRIs are not usually recommended for treating mild depression because there are more effective treatments such as exercise therapy.

However, exceptions can be made if:

  • your symptoms of mild depression have lasted for more than two years, or
  • you have experienced previous episodes of moderate or severe depression

Other mental health conditions

SSRIs can also be used to help treat other mental health conditions, including:

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