Side effects
Please do not be worried by the side effects listed on this page. Many people take fluoxetine without any side effects or only a few mild side effects. Starting with a lower dose can sometimes help if side effects do occur.
Side effects that do appear should disappear or get better after a few days. If they do not, you should go back to your doctor.
Do not stop taking the fluoxetine until you talk to your doctor, or you may get withdrawal symptoms as well.
Very common side effects when taking fluoxetine (affecting more than one in ten people) include:
- insomnia (sleep problems)
- headache and feeling tired
- diarrhoea (loose poo)
- nausea (feeling sick)
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
- 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, urticaria), 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.
Please look at the leaflet inside your medicine box, or ask a doctor or pharmacist, if you want to know whether you are getting a side effect from your medicine.
If you do get a side effect, please think about reporting it via the Yellow Card Scheme.
Body
Your weight can be affected by fluoxetine.
A side effect of fluoxetine can be not feeling as hungry as normal, which might lead to weight loss.
It is very difficult to know how this will affect each person who takes it.
Talk to your doctor about this if it worries you.
Sleep
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. This should settle after a couple of weeks.
If you feel very sleepy, and you’ve been taking it for more than a month, you should go back to the doctor and see what else you could do.
Sex and fertility
Sex
Fluoxetine can have side effects that might affect your sex life. These include:
- painful erections that last for a long time (this is rare but serious - visit a hospital or see your doctor straight away if you experience this side effect), or problems getting an erection (getting hard) and ejaculating (coming)
- bleeding from the vagina
- difficulty reaching orgasm the same way as before
- some growth of the breasts and some milk flow, regardless of gender
- you may have a lower sex drive
Fluoxetine has been known to slow growth and delay sexual development (puberty) in a small number of children and young people. Your doctor should check your growth while you are taking it. If this worries you, talk to your doctor or pharmacist about it.
These effects should pass after the first couple of weeks. If they do not, and this is a problem for you, go back to the doctor and see what else you could try.
The good effects of fluoxetine may, after a while, have a positive impact on your sex life as your mood lifts and you become interested in life and relationships again.
Fertility
Fluoxetine does not seem to affect human fertility.
Talk to your doctor about your fluoxetine if you are trying to get pregnant.
Pregnancy, post-natal and breastfeeding
Pregnancy
If you become pregnant while you are on fluoxetine, you should carry on taking the medicine and go back to your doctor as soon as possible, to see if you should change or stop your medicine.
There is a slightly higher risk of problems in the developing baby if you take fluoxetine it in the early stages of pregnancy. However, fluoxetine and related antidepressants (known as SSRIs) are thought to be better choices if you need antidepressant medicine.
Remember that you need to stay well through your pregnancy, and you may need a medicine to help you to do that.
Fluoxetine may cause heart problems in the developing baby, and other symptoms in new-born babies.
If you and your doctor agree that you will continue taking fluoxetine during your pregnancy, then you should tell your midwife that you are taking it before you give birth.
Post-natal
If fluoxetine is taken in the last five months of a pregnancy, it can cause a serious condition called persistent pulmonary hypertension of the new-born (PPHN). This 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.
PPHN appears in the first 24 hours after birth. You will need help from the midwife and doctors, so it is better if they are looking out for symptoms.
The newborn baby may also develop withdrawal effects, which might not appear straight away but might develop over the first few days of life. These could include:
- being irritable and crying a lot
- having difficulty sleeping or sucking
- poor weight gain
Breastfeeding
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.
The amount of fluoxetine in breast milk is usually around 7% of the mum’s dose, but it can build up over time. This is because fluoxetine is hard for your baby to get rid of. This does not mean breastfeeding will be a problem, but do look out for side effects.
If your baby was premature or has health problems, then you may be better off not breastfeeding as your baby will likely struggle even more to get rid of the fluoxetine.
Talk to your doctor or midwife about your feeding options.
Driving and transport
Do not drive or ride a bike just after you start taking fluoxetine.
Taking fluoxetine may affect your ability to do things like drive a car, ride a bike, use machines, or anything else that needs a lot of focus.
It might be best to stop doing these things for the first few days, until you know how it affects you, or until the effects pass.
Do not worry - most people drive as normal while taking fluoxetine.
School and exams
Try not to take fluoxetine for the first time just before your exams.
Taking fluoxetine may affect your ability to do things that need a lot of focus, like 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 to study.
Do not worry - most people do exams as normal while taking fluoxetine.
Friends and family
You may want to let your family and friends know you are taking fluoxetine so they can support you and help you look out for side effects.
For guidance on this, check out our page on getting support with your medication.
Sport
Fluoxetine is not a banned substance in sport.
Taking fluoxetine may affect your ability to do things like riding a bike, competitive gymnastics, or anything else that needs a lot of focus.
It might be best to stop such sports for the first few days, until you know how it affects you or the effects get better.
Do not worry - most people play sports as normal while taking fluoxetine.
Alcohol and street drugs
Alcohol
You can continue 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.
Drinking alcohol every day, however, can make the symptoms of depression worse and you will not feel the benefit of your medicine.
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 days, it might be best to stop drinking alcohol until you see how the medicine affects you, or until the effects pass.
Street drugs
Be careful if you are also using 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. For more information, have a look at our drugs and alcohol page.
Methadone and fluoxetine together can seriously affect your heart so these should only be combined under doctor supervision.
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.
Prescription medicines
Fluoxetine does not mix well with some other medicines and drugs.
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.
Tell your doctor or pharmacist before you take fluoxetine if you are prescribed any other medication, to check that the combination is safe.
Before you start taking fluoxetine, tell your doctor if you are taking any other medications, including things you have bought over the counter for common illnesses like colds and flu or topical applications that you put on your skin.
References and further reading
For more helpful links and information, have a look at our references and further reading page.