Fluoxetine | SSRI Uses, Warnings & Side Effects

Medication name

Fluoxetine ("Flu-OX-et-een")
Brand name

Prozac ("PRO-zak")
Medication type

Selective serotonin reuptake inhibitor (SSRI)

Capsules: 10mg, 20mg, 30mg, 40mg and 60mg strengths

Liquids: 20mg per 5ml spoonful

Tablets: 10mg strength

Dispersible tablets*: 20mg strength

*These tablets may be dispersed in water before taking or swallowed whole. The tablets can be broken in half to get a 10mg dose if needed.

If you are 18 or over, fluoxetine can be prescribed for you as a licensed medicine to treat depression, bulimia nervosa or obsessive compulsive disorder (OCD).

If you are aged eight to 17 years old, a doctor can prescribe fluoxetine to treat depression (low mood) in combination with talking therapies (if talking therapies have not helped you feel better on their own). If you don’t want to try talking therapies, your doctor can still consider fluoxetine as a treatment option.

If you are under 18, your doctor may also consider this medicine for anxiety, obsessive-compulsive disorder or bulimia nervosa.

Read our guide to depression

About fluoxetine

Fluoxetine is a type of antidepressant called a selective serotonin reuptake inhibitor (SSRI).

Serotonin (also called '5HT') is a naturally occurring chemical messenger (or ‘neurotransmitter’) that has an important role in areas of the brain that control mood, thinking, feelings and emotions. Research suggests that depression or low mood is more likely to occur when the brain doesn’t have enough serotonin.

Selective serotonin reuptake inhibitors (SSRIs) like fluoxetine are thought to work by increasing levels of serotonin in the brain.

Depression, and other conditions like anxiety disorders, are not just caused by low serotonin levels, but a rise in serotonin levels can improve symptoms and help you to feel better.

Fluoxetine and everyday life

Fluoxetine should start helping with depression within one to two weeks. It may take four weeks or longer for you to get the full effect.

How people respond to treatment can vary. Sometimes improvement is slow, and you may not feel any different to start with. This can be hard when your mood is low, and if you experience any side effects form your medication you may think you feel worse and not better. If you can, give your medication a chance to work and continue to take it for at least three to four weeks to see if it makes a difference.

Your parents, friends and doctor may notice an improvement in you before you feel it yourself, so it’s a good idea to talk to them.

If you think your medicine has not made any difference to how you feel after three to four weeks, you should go back to your doctor. They might recommend a change in dose or a different medication. However, it can take longer to work for some people than for others, so they may suggest you wait six to eight weeks before deciding.

For anxiety or obsessive-compulsive disorder, it may take longer for the benefits to be noticed. It could take up to three months before you feel the full benefit.

For some people, anxiety symptoms briefly increase at the start of treatment, but the anxiety should decrease over time as you continue to take your medicine. To avoid or minimise this, your doctor will usually start treatment with a low dose and increase this after one to two weeks.

Fluoxetine can make you feel less hungry than normal, which might lead to weight loss.

It is not possible to predict how fluoxetine will affect each person before they start taking it. Talk to your doctor or pharmacist if you are concerned about your weight, or changes to your weight, while taking fluoxetine.

A common side effect of fluoxetine is a dry mouth. Over a long time, this can increase your risk of developing tooth decay or gum disease. Make sure you brush your teeth well and have regular dental check-ups. Speak to your dentist, doctor or pharmacist about things you can do to help.

You may want to let your family and friends know you are taking fluoxetine effects.

For guidance on this, check out our page on getting support with your medication.

You can feel drowsy in the first few days of taking fluoxetine. However, it should get better after the first week or two.

You may become more anxious, or it may make you irritable which may also affect your sleep. If you experience this, it should settle after a couple of weeks. If these symptoms are very bad, or they continue for more than a couple of weeks, discuss this with your doctor
Some people find that fluoxetine makes them feel more alert or causes insomnia (difficulty getting to sleep). If this happens, try taking fluoxetine first thing in the morning.

If you find that fluoxetine is still affecting your sleep (either making you feel very sleepy or disrupting your sleep), and you’ve been taking it for more than a month, discuss this with your doctor or pharmacist.

Alcohol

It may be possible to drink some alcohol while taking fluoxetine, but it is best to do so in moderation. Fluoxetine can sometimes cause drowsiness as a side effect, so it is possible that alcohol might make you feel more drowsy than usual.

Side effects might make you sleepy or you might lose your focus when you first start taking fluoxetine. This could be dangerous if you drive or use machines or do anything that needs a lot of focus.

During the first few weeks of treatment, it might be best to stop drinking alcohol until you see how the medicine affects you.

Drinking alcohol every day or in large amounts can make your symptoms worse and may mean you won’t get the maximum benefit from your medication.

Street drugs

Cannabis can have unpredictable effects when taken with fluoxetine, so great care is needed.

Cannabis and other drugs may have their own side effects on your mental health, like anxiety or psychosis.

Methadone and fluoxetine together can seriously affect your heart. (In some situations, methadone may be prescribed by your doctor. Fluoxetine and methadone can be prescribed together- but your doctor would monitor this very carefully)

Fluoxetine has been shown to dampen down the 'high' of cocaine.

Taking fluoxetine with cocaine, ecstasy or amfetamines could bring on serotonin syndrome. You could get a high temperature/fever, agitation, confusion, trembling or weird muscle movements. You need to go to hospital if this happens. Tell the doctor everything that you have taken.

Fluoxetine can produce a false positive test for amfetamines and LSD on a urine drug screen. Talk to your doctor about this if it is a problem for you.

There are many other street drugs, but we don’t know what effect taking them with fluoxetine will have, so it’s best to be cautious. There is no regulation of street drugs or ‘legal highs’, so even if there are no known issues with the medication you take, the supply you receive might be mixed with other substances that could be dangerous.

Get more advice on drugs and alcohol.

Fluoxetine does not mix well with some other medicines, including herbal medicines. It may affect how they work or could cause more side effects.

Do not take fluoxetine if you take an antidepressant medicine called a monoamine oxidase inhibitor (MAOI), or if you have taken one in the last two weeks. MAOIs include moclobemide, isocarboxazid, phenelzine and tranylcypromine.

Before you start taking fluoxetine, tell your doctor if you are taking any other medications, including things you have bought from a pharmacy (or other shop) for common illnesses like colds and flu. This includes medications that you put on your skin.

Look at the leaflet inside your medicine box for more information about other medicines that can interact with fluoxetine. With some medicines your doctor may need to adjust the dose of your medicines if you take them together. Ask a doctor or pharmacist for more information if you have any questions.

There are multiple companies that manufacture fluoxetine and multiple forms available, including capsules, dispersible tablets, tablets and liquids. The non-active ingredients vary between products and manufacturers, so if you have any food allergies or intolerances, always let your pharmacist know.

The liquid medication includes a small amount of alcohol, but not enough to affect your blood alcohol level. The liquid medication may also contain sucrose. A sugar-free alternative is available.

If you need to avoid animal products such as gelatine, please note that this is used in the manufacturing process for fluoxetine capsules.
Further information about practical considerations for medicines if you need to avoid animal products can be found on the Vegan Society website.

Taking fluoxetine may affect your ability to do things like driving a car, riding a bike, or anything else that needs a lot of focus or balance. It can make you tremble, feel dizzy or restless when you first start taking the medication.

It is recommended that you stop driving or riding a bike for the first few days or weeks until you know how it affects you.

Most people drive as normal while taking fluoxetine. If you are worried about this or have any concerns you would like to discuss, speak to your doctor or pharmacist.

Pregnancy

If you become pregnant while you are on fluoxetine, you should carry on taking the medicine and make an appointment to see your doctor as soon as possible. They can discuss the benefits and risks of continuing fluoxetine and help you to make a decision that is best for you and your baby. They may refer you to a specialist perinatal mental health team to support you with this decision.

You can find out more information about taking fluoxetine during pregnancy at Bumps (Best Use of Medicines in Pregnancy).

Untreated depression or anxiety (or other mental illness) can also be harmful to you and your developing baby, so decisions about stopping or avoiding medication when you are pregnant need to be discussed carefully with your doctor. If you and your doctor agree that carrying on with fluoxetine has more benefits than risks, you should tell your midwife that you are continuing to take this at your next appointment.

Some research has reported that taking SSRI antidepressants during the month before delivery can result in a small increased risk of bleeding after you have given birth. It will be important for your doctor and midwife to know what medication you are taking so that appropriate monitoring and treatment is planned. If you are concerned about this discuss it with your doctor and midwife.

If you are planning to get pregnant, it is recommended that you take folic acid while you are trying for a baby and during pregnancy. It is safe to take this together with fluoxetine.

Post-natal

If fluoxetine is taken in the last five months of a pregnancy, studies have shown a small increased risk of persistent pulmonary hypertension of the new-born (PPHN). This occurs in the first 24 hours after birth and can make the baby breathe faster and look a bit blue in colour. PPHN affects around three in 1,000 babies born to mums who take SSRIs. This compares with a rate of two in 1,000 among babies born to mums who do not take SSRIs. More recent research has failed to reproduce this finding. If you are concerned about this, talk to your doctor and midwife. If this does occur, you will need help from your midwife, so it is important they are looking out for symptoms.

There are some other symptoms that can occur in new-born babies if fluoxetine is taken in the last three months of pregnancy, look out for these and get help if they happen:

jerking or twitching of the muscles or shaking
being jittery, irritable or constant crying
being too hot or cold
suckling/ feeding difficulties or being sick
having stiff or floppy muscles, or overactive reflexes
being very sleepy or finding it difficult to sleep

These are usually mild and go away in a few days without treatment.

Breastfeeding

Talk to your doctor, midwife or pharmacist if you want to breastfeed while taking fluoxetine.

Some fluoxetine is passed to the baby in breast milk, and side effects have been seen in breastfed babies. The main one is likely to be colic. However, the level of fluoxetine detected in breast milk is still considered safe if you are taking fluoxetine and want to breastfeed.

If you breastfeed while taking fluoxetine, seek urgent medical advice if your baby becomes restless, very sleepy, or develops feeding problems.

If your baby was born early or has health problems, then breastfeeding while taking fluoxetine may not be recommended. Talk to your midwife and doctor about feeding options.

If your medication makes you sleepy, do not to sleep with your baby in the same bed, and be cautious when handling your baby (especially if waking during the night for feeds).

Sex

Fluoxetine can have side effects that might affect your sex life. These include:

painful erections, problems with getting an erection (getting hard) and ejaculating (coming)
bleeding from the vagina and difficulty reaching orgasm (coming) the same way as before or not being able to have an orgasm at all
reduced genital sensation
lower sex drive

Most side effects occur when you first start medication and improve over time. If they do not, and this is a problem for you, make an appointment to discuss this with your doctor.

Some other rare side effects include breast growth or milk flow from the breasts. These may affect your confidence and therefore your desire to have sex. Talk to your doctor if you get these symptoms.

There is some evidence to indicate that some side effects affecting your sex life might continue for several months or longer after you stop your medicine. This is sometimes referred to as PSSD (post SSRI sexual dysfunction). More research is needed to understand how frequently this might happen. Discuss this with your doctor or pharmacist is you are concerned.

Fluoxetine has been known to slow growth and delay puberty in a small number of children and young people. Your doctor should check your growth while you are taking it. If you are concerned about this, talk to your doctor or pharmacist about it.

Untreated depression or anxiety can have a negative effect on your sex life, so if fluoxetine helps you to recover, positive effects can include improving your desire, experience and enjoyment of sex as your mood lifts and you become interested in life and relationships again.

Fertility

There is no evidence to show that fluoxetine affects fertility.

Talk to your doctor about your fluoxetine if you are trying to get pregnant.

Fluoxetine is not a banned substance in sport.

Most people play sports as normal while taking fluoxetine. Taking fluoxetine may affect your ability to do things like riding a bike, competitive gymnastics, or anything else that needs a lot of focus. Fluoxetine may make you feel very restless in the first few weeks so you may find it difficult to sit or stand still when you first start this medicine.

It might be best to stop sports for the first few days until you know how it affects you or the effects get better.

If you are worried that taking fluoxetine might make doing the sports you enjoy more difficult, discuss this with your doctor.

Ideally it is best not to take fluoxetine for the first time just before your exams. It is not possible to predict how the medication will make you feel, and if you do get any side effects, these are more likely to occur when you first start taking fluoxetine.

Taking fluoxetine may affect your ability to do things that need a lot of focus, it may also affect your sleep and make you feel more anxious or restless, which might interfere with your preparation for exams.

You should talk to your doctor about any future exams if you are starting fluoxetine. You might decide together to delay starting it until you have done them. If they are more than a month away, however, you might find that it is better to start fluoxetine to lift your mood and improve your motivation and ability to study.

Most people take exams as normal while taking fluoxetine. It you are worried that taking fluoxetine might make studying for or taking your exams harder, discuss this with your doctor.

Information and safety considerations

Your doctor will consider any other medical conditions or symptoms you have before recommending a medicine for you.

Your medicine will come with a ‘patient information leaflet’. It’s important that you read this information. Speak to your pharmacist if:

you’re not given a leaflet
you don’t understand the information
you need it in a different format or language
you’re concerned about something you’ve read

The information leaflet also includes a list of warnings and precautions to consider before you take the medicine. If you think that any of these apply to you and are concerned that your doctor is not already aware of them, check with your doctor or pharmacist before you start to take your medication (or as soon as possible if you are already taking it).

Uses, warnings, safety and side effects

Taking fluoxetine

Your doctor will advise you on how long it is best to keep taking your medication. This may vary depending on what you’re taking it for and how many times you’ve been unwell.

If you are prescribed fluoxetine for low mood or depression, it is recommended that you take it for at least six months after you feel well again. This means that most people take it for at least seven to nine months. Research has shown that stopping it sooner, or immediately after you start to feel better, increases the risk of your low mood returning.

If you have had low mood or depression more than once, or if there is a higher risk of you becoming unwell again, your doctor may advise you to continue fluoxetine for at least two years after you feel well again.

If you are prescribed fluoxetine for anxiety or obsessional-compulsive disorder (OCD), it is recommended that you take fluoxetine for at least one year after you feel well again. Research has shown that stopping it sooner, or immediately after you start to feel better, increases the risk of your symptoms returning.

If you have bipolar disorder, it is likely that the doctor will advise for the fluoxetine to be stopped sooner. This is because, in bipolar disorder, there is a risk of your mood becoming too high if an antidepressant is used for too long.

You will get the best effect from fluoxetine if you take it every day at the dose prescribed by your doctor.

Your doctor might start you on a low dose and then increase it to your full dose slowly over two to four weeks.

Depending on your age and condition, your doctor may prescribe a lower dose of medication to start with. This might mean you are prescribed fluoxetine liquid to start with and then switch to capsules when the dose increases.

It is usually best to take fluoxetine in the morning. This is to reduce the chance of it causing difficulty sleeping. However, some people find this medicine makes them feel tired, so you may prefer to take it in the evening instead.

When you have worked out what time of day is best for you, it is recommended that you take your medication at roughly the same time every day. Try to get into a routine, like taking it when you have breakfast or brush your teeth.

Fluoxetine is best taken after food. This helps to minimise side effects like feeling sick.

Swallow the tablet or capsule whole with a drink of water – if you chew the tablet or open the capsule, it tastes bitter.

Dispersible tablets may be swallowed whole with water or other liquid, or can be dispersed in a small volume of water and swallowed immediately.

If you miss a dose during the day, just take it as soon as possible.

If you forget to take it by the time of your next dose, just take the next dose. Do not try and catch up by taking a double dose.

If you forget to take it for a few days, you may start getting withdrawal symptoms. These should improve quickly after you start taking fluoxetine again. If they do not, seek advice from your doctor or pharmacist.

If you regularly forget to take it every day, your medicine may not work as well and it could increase the risk of you becoming unwell again.

Many people who take 20mg or less of fluoxetine can stop taking it without problems. For people on higher doses of fluoxetine, the dose may be stepped down over a few weeks to reduce the chance of withdrawal effects.

If you have been taking fluoxetine regularly for more than one to two months, it is recommended that you stop gradually (ideally over at least four weeks).

Discuss stopping your medication with your doctor. If you have important events coming up or are going through a period of life which is very demanding, it might not be the best time to stop your medication. Planning and support are important to stopping your antidepressant medication successfully.

Antidepressants are not addictive, but if stopped suddenly they can cause discontinuation or withdrawal symptoms. These are caused by the receptors and levels of chemical transmitters in your brain readjusting after you reduce or stop your medication (and can also occur if you miss doses of medication).

Fluoxetine is less likely to cause withdrawal effects when stopped compared with some other antidepressants. This is because your body takes longer to get rid of it and the levels of medicine reduce gradually over four to six weeks after you stop it. This may mean you experience some milder withdrawal effects several weeks after stopping the medication and may not associate it with stopping the fluoxetine.

Some of the symptoms you get may be like symptoms you had when you were unwell, so understandably, you might feel anxious or upset that your illness could be returning.

If you experience symptoms immediately or soon after stopping medication (days rather than weeks), this is usually a withdrawal symptom caused by your body adjusting to not having the medication anymore. If the symptoms start after a month or more after stopping your medicine, this might be a sign that you are becoming unwell again.

Withdrawal symptoms usually start within a few days of stopping (or sometimes reducing) your medication. A wide range of symptoms have been reported and are listed below. You may experience a few or a range of these:

dizziness and/or feeling unsteady
headaches
numbness or tingling in hands or feet
sleep disturbances (vivid dreams, nightmares, not being able to sleep)
electric shock-like feelings in the head, spine, arms, legs or hands
feeling anxious, agitated or irritable and/or restless
confused or disorientated and reduced concentration
poor appetite, feeling or being sick or having diarrhoea (loose poo)
sweating or shaking
feeling emotional, low mood and tearful
flu-like symptoms/muscle aches and pains
tinnitus (ringing in your ears)
problems with your eyes, or fluttering/pounding heartbeat (this is not as common as the other symptoms listed above)

It is not possible to predict if you will experience withdrawal symptoms (or how bad they will be if you do experience them) but studies report about half of people may get them. The risk appears to be higher if:

you have been taking your medication for six to eight weeks and you stop taking it suddenly
you are a child or young person
you experienced an increase in anxiety symptoms when you started medication
you have experienced withdrawal symptoms with another antidepressant before

If you do experience symptoms, they are usually mild and don’t last long (two to three weeks for most people) , but for a few these could be severe enough to make you feel very unwell and last longer (two to three months or more). Arrange an appointment with your doctor to discuss your symptoms and seek advice if you are concerned or unable to tolerate them.

You can stop taking fluoxetine safely with your doctor’s help. Planning a gradual withdrawal together can help to minimise or prevent the withdrawal symptoms you experience.

Warnings and safety

If you have taken more than the dose prescribed by your doctor, contact NHS 111 immediately to ask for advice, or ask a family member or friend to do this for you. This is important even if you don’t feel any different.

NHS 111 can give you advice and direct you to the best place to get more help if you need it.

If you have taken too much medication on purpose, or if after taking this you quickly feel unwell, call 999 or get someone to take you to A&E straight away. This includes any of the following signs:

feeling sick or being sick
having seizures (fits)
an irregular heartbeat or a heart attack
breathing difficulties
a change in the way you feel, ranging from agitation to losing consciousness

If you need to go to A&E, do not travel alone or drive yourself there. Get your parent, family member or friend to go with you to support you and keep you safe on the way. If someone is not able to drive you there, call for an ambulance. Take your medication with you and tell doctors how much you have taken.

Suicidal thoughts

Depression (and other mental illnesses) can sometimes cause you to have thoughts about hurting yourself or taking your own life. While uncommon, this could also be a side effect of your medicine. This can happen to anyone but is more likely to happen if you are under 25 years old.

If you have any thoughts like this, it is important you get urgent help. Contact your doctor immediately for advice and support. This could be your GP or specialist mental health team. If you are able, share how you are feeling with family member or friend as well so they can support you to get help.

If you discussed with your doctor what to do if you get these thoughts and created a safety plan, read this to remind you who to contact for support and what you can do to help you cope.

Read our guide to suicidal feelings

Serious side effects

Fluoxetine can cause rare but serious side effects, including allergic reactions.

Stop taking fluoxetine and go to a hospital straight away if you get any of the following symptoms:

difficulty breathing
an allergic reaction or allergy (include symptoms such as swelling of your face, eyelids, lips, tongue or throat so that you cannot swallow or breathe, or really bad itching of the skin with raised lumps)
rashes, blotches, itching, blistering, redness, peeling, or ulcers on your skin, in your mouth, or in your genital area (these can be symptoms of a rare but serious skin reaction)
fast, uneven heartbeat and fainting (this could mean a life-threatening condition called Torsades de Pointes)
any combination of the following symptoms: high fever, agitation, confusion, trembling, sweating, diarrhoea (loose poo), fast heartbeat or weird movements of your muscles (this could be serotonin syndrome)
you start having seizures or fits for the first time
a painful erection (priapism) that lasts longer than three hours

Get your parent, family member or friend to take you or go with you to support you and keep you safe on the way. If someone is not able to drive you there, call for an ambulance. Take your medication with you.

Contact your doctor immediately but don't stop taking fluoxetine, if you get any of the following symptoms:

your behaviour changes because you feel very happy or over-excited or experience severe irritability or agitation
any unusual bleeding, including blood in your poo
you experience tiredness, confusion and muscle-twitching (you may have a low blood-level of sodium)
yellowing of the skin or whites of the eyes (your liver may not be working properly)
if fits that you have had in the past happen more often
restlessness, or difficulty sitting or standing still
dizziness, feeling sick or being sick

If you are unable to contact your doctor, call NHS 111 for urgent advice.

Side effects and your health

Side effects are more common when you first start taking fluoxetine. Many go away as you continue your medicine. If they don’t get better, or if you are worried by them and they are causing you distress, speak to your doctor or pharmacist about them. When starting your medicine, your doctor will usually prescribe a low dose and increase this gradually. This helps to reduce the risk of you getting side effects.

Very common side effects when taking fluoxetine (affecting more than one in ten people) include:

insomnia (sleep problems) – try taking your dose first thing in the morning
headache and feeling tired
diarrhoea (loose poo)
nausea (feeling sick) – try taking your fluoxetine with or just after food

Common side effects of taking fluoxetine (affecting up to one in ten people) include:

not feeling hungry
weight loss
nervousness, anxiety, restlessness, poor concentration, feeling tense
decreased sex drive or sexual problems, including difficulty maintaining an erection (staying hard)
sleep problems, unusual dreams, tiredness or sleepiness
dizziness
change in taste, or dry mouth (this can increase the risk of tooth decay, so clean your teeth more often than usual and avoid drinking sugary drinks)
uncontrollable shaking movements
blurred vision
heartbeat feels quick and uneven
flushing, sweating more, feeling shaky or chills
yawning
indigestion, being sick
rash, itching lumps, hives or other skin itching
joint pain
needing to wee more often
unexplained vaginal bleeding

There are other side effects that you can get when taking this medicine. We have only included the most common ones here.

This list of side effects can look scary. You may not experience any of them, but it’s important to be aware of them so you know what to do if they do happen.

Unless your side effects are very severe or distressing, try to continue taking your medication until you can talk to your doctor. Your doctor can make changes to your medication to help if needed.

Uncommon but important side effects to be aware of include thoughts of harming yourself, thinking about taking your own life or trying to take your own life. This may be a symptom of your illness, including depression, but may be a side effect of medication. If you experience these thoughts, contact your doctor to seek immediate support to keep you safe.

Your doctor will make sure you are monitored carefully for these side effects, and you should decide with your doctor what to do if you experience these feelings while taking fluoxetine. It’s a good idea to write these plans down and keep them somewhere safe.

If you are taking fluoxetine and have not talked about this with your doctor, go back to them and talk it through. You might also want to talk to your parents, family member or friend about it too.

Another uncommon side effect is an increase in your risk of bleeding, including intestinal (stomach or gut) bleeding. Let your doctor know if you vomit blood or develop black or blood-stained poo.

There is no routine monitoring recommended before starting or while you are taking fluoxetine, although your doctor may recommend specific tests, like a blood test, to help them make decisions about your medication.