- It usually takes 4 to 6 weeks for fluoxetine to work.
- Common side effects include feeling sick (nausea), headaches and trouble sleeping. They are usually mild and go away after a couple of weeks.
- If you and your doctor decide to take you off fluoxetine, your doctor will probably recommend reducing your dose gradually to help prevent extra side effects.
- Fluoxetine is called by the brand name Prozac.
Fluoxetine can be taken by adults for depression, obsessive compulsive disorder and bulimia.
Fluoxetine can be taken by children aged 8 years or older for depression.
Check with your doctor before starting to take fluoxetine if you:
- have had an allergic reaction to fluoxetine or any other medicines in the past
- have a heart problem, as fluoxetine can speed up or change your heartbeat
- have ever taken any other medicines for depression. Some rarely used antidepressants can interact with fluoxetine to cause very high blood pressure even when they have been stopped for a few weeks.
- are trying to become pregnant, are already pregnant or you are breastfeeding
- have an eye problem called glaucoma because fluoxetine can increase the pressure in your eye
- have epilepsy or are having electroconvulsive treatment - fluoxetine may increase the risk of having a seizure
If you have diabetes, fluoxetine can make it more difficult to keep your blood sugar stable. Monitor your blood sugar more often for the first few weeks of treatment with fluoxetine and adjust your diabetes treatment if necessary.
Take fluoxetine once a day. You can take it with or without food.
You can take fluoxetine at any time, as long as you stick to the same time every day. If you have trouble sleeping, it's best to take it in the morning.
How much to take
The usual dose of fluoxetine is 20mg a day in adults. However, you may be started at a lower dose which is gradually increased to a maximum dose of 60mg a day. Some people might need to take a lower dose of fluoxetine, or to take it less often. This includes people with liver problems, and elderly people.
The usual dose of fluoxetine in children is 10mg a day but this may be increased to 20mg a day.
What if I forget to take it?
If you occasionally forget to take a dose, don't worry. Take your next dose the next day at the usual time. Never take 2 doses at the same time to make up for a forgotten one.
If you forget doses often, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.
What if I take too much?
The amount of fluoxetine that can lead to an overdose varies from person to person.
Call a doctor straight away if:
You've taken too much fluoxetine by accident and experience symptoms such as:
- being sick (vomiting)
- feeling sleepy
- feeling agitated
- heart problems
- lung problems
- fits (seizures)
If you need to go to a hospital accident and emergency (A&E) department, do not drive yourself - get someone else to drive you or call for an ambulance.
Take the fluoxetine packet, or the leaflet inside it, plus any remaining medicine with you.
Like all medicines, fluoxetine can cause side effects in some people, but many people have no side effects or only minor ones. Some of the common side effects of fluoxetine will gradually improve as your body gets used to it.
Common side effects
These side effects happen in more than 1 in 100 people. Keep taking the medicine, but tell your doctor or pharmacist if these side effects bother you or don't go away:
- feeling sick (nausea)
- being unable to sleep
- feeling tired or weak
Serious side effects
It happens rarely (in less than 1 in 100 people), but some people may have serious side effects when taking fluoxetine.
Go to A&E immediately if you get:
- chest pain or pressure, or shortness of breath
- severe dizziness or passing out
- painful erections that last longer than 4 hours - this may happen even when you are not having sex
- any bleeding that is very bad or that you cannot stop, such as cuts or nosebleeds that don't stop within 10 minutes
Call a doctor straight away if you get:
- headaches, trouble focusing, memory problems, not thinking clearly, weakness, seizures, or losing your balance - these can be signs of low sodium levels
- thoughts about harming yourself or ending your life
- fits, feelings of euphoria, excessive enthusiasm or excitement, or a feeling of restlessness that means you can't sit or stand still
- vomiting blood or dark vomit, coughing up blood, blood in your pee, black or red poo - these can be signs of bleeding from the gut
- bleeding from the gums or bruises that appear without a reason or that get bigger
Book an appointment with a doctor if you experience:
- weight gain or weight loss without trying
- changes in your periods such as heavy bleeding, spotting, or bleeding between periods
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to fluoxetine.
Call 999 or go to A&E if:
- you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
- you're wheezing
- you get tightness in the chest or throat
- you have trouble breathing or talking
- your mouth, face, lips, tongue or throat start swelling
You could be having a serious allergic reaction and may need immediate treatment in hospital.
These are not all the side effects of fluoxetine. For a full list see the leaflet inside your medicines packet.
You can report any suspected side effect to the UK safety scheme.
You can reduce the chance of having a side effect if you take fluoxetine in the evening so that you're asleep when the level of medicine in your body is highest.
What to do about:
- feeling sick (nausea) - try taking fluoxetine with or after food. It may also help to stick to simple meals and avoid rich or spicy food.
- headaches - make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Ask your pharmacist to recommend a painkiller. Headaches should usually go away after the first week of taking fluoxetine. Talk to your doctor if they last longer than a week or are severe.
- being unable to sleep - take fluoxetine first thing in the morning
- diarrhoea - drink plenty of water or other fluids to avoid dehydration. Signs of dehydration include peeing less than usual or having dark strong-smelling pee. Do not take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor.
- feeling tired or weak - if fluoxetine makes you feel tired or weak, stop what you're doing and sit or lie down until you feel better. Do not drive or use tools or machinery if you're feeling tired. Do not drink alcohol as it will make you feel worse. If these symptoms don't go away after a week or two, ask your doctor for advice.
It's important for you and your baby that you stay well during your pregnancy. If you become pregnant while taking fluoxetine speak to your doctor. Do not stop taking your medicine unless your doctor tells you to.
Fluoxetine has been linked to a very small increased risk of problems for your unborn baby. However, if your depression is not treated during pregnancy this can also increase the chance of problems.
You may need to take fluoxetine during pregnancy if you need it to remain well. Your doctor can explain the risks and the benefits, and will help you decide which treatment is best for you and your baby.
For more information about how fluoxetine can affect you and your baby during pregnancy, read this leaflet on the Best Use of Medicines in Pregnancy (BUMPS) website.
Fluoxetine and breastfeeding
If your doctor or health visitor says your baby is healthy, fluoxetine can be used during breastfeeding. It has been used in many breastfeeding mothers without any problems.
Fluoxetine passes into breast milk, usually in small amounts. It has been linked with side effects in very few breastfed babies.
It is important to continue taking fluoxetine to keep you well. Breastfeeding will also benefit both you and your baby.
If you notice that your baby isn't feeding as well as usual, or seems unusually sleepy, or if you have any other concerns about your baby, then talk to your health visitor or doctor as soon as possible.
Tell your doctor if you're:
- trying to get pregnant
Some medicines and fluoxetine can interfere with each other and increase the chances of you having side effects.
Tell your doctor if you're taking these medicines before you start fluoxetine:
- any medicines that affect your heartbeat - as fluoxetine can speed up or change your heartbeat
- any other medicines for depression. Some rarely used antidepressants can interfere with fluoxetine to cause very high blood pressure even when they have been stopped for a few weeks.
Mixing fluoxetine with herbal remedies and supplements
Do not take St John's wort, the herbal remedy for depression, while you are being treated with fluoxetine as this will increase your risk of side effects.
Tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.
How does fluoxetine work?
Fluoxetine is one of a group of antidepressants called selective serotonin reuptake inhibitors, or SSRIs. These medicines are thought to work by increasing the levels of a mood-enhancing chemical called serotonin in the brain.
When will I feel better?
You may see an improvement in your symptoms after 1 to 2 weeks, although it usually takes between 4 and 6 weeks before you feel the full benefits. That's because it takes around a week for fluoxetine levels to build up in your body, and then a few weeks longer for your body to adapt and get used to it.
Do not stop taking fluoxetine after 1 to 2 weeks just because you feel it is not helping your symptoms. Give the medicine at least 6 weeks to work.
How will it make me feel?
Antidepressants like fluoxetine help to jump start your mood so you feel better.
You may notice that you sleep better and get on with people more easily because you're less anxious. You will hopefully take in your stride little things that used to worry you.
Fluoxetine won't change your personality or make you feel euphorically happy. It will simply help you feel like yourself again.
Don't expect to feel better overnight, though. Some people feel worse during the first few weeks of treatment before they begin to feel better.
How long will I take it for?
Once you're feeling better it's likely that you will continue to take fluoxetine for several more months.
Most doctors recommend that you take antidepressants for 6 months to a year after you no longer feel depressed. Stopping before that time can make depression come back.
Is it safe to take it for a long time?
For most people, fluoxetine is safe to take for a long time.
A few people may get sexual side effects, such as problems getting an erection or a lower sex drive. In some cases these can continue even after stopping the medicine. Speak to your doctor if you are worried.
Otherwise there don’t seem to be any lasting harmful effects from taking fluoxetine for many months and years.
How do I come off fluoxetine?
If you've been feeling better for 6 months or more, your doctor may suggest coming off fluoxetine.
Your doctor will probably recommend reducing your dose gradually over several weeks - or longer, if you have been taking fluoxetine for a long time.
This is to help prevent any extra side effects you might get as a reaction to coming off the medicine. These include:
- feeling sick
- numbness or tingling in the hands or feet
- trouble sleeping
- feeling agitated or anxious
Do not stop taking fluoxetine suddenly, or without talking to your doctor first.
Is fluoxetine better than other antidepressants?
Fluoxetine isn't any better or worse than other antidepressants.
However, sometimes people respond better to one antidepressant than to another. Talk to your doctor if you aren't feeling any better after 6 weeks.
Will it affect my contraception?
Will it affect my fertility?
There's some evidence that fluoxetine can reduce the quality of sperm - but it's not known whether this reduces male fertility. The effect should reverse once you stop taking the medicine. Speak to your doctor if you're concerned.
For women, there's no firm evidence to suggest that taking fluoxetine will reduce your fertility. However, speak to a pharmacist or your doctor if you're trying to get pregnant. They may want to review your treatment.
Will it affect my sex life?
The good effects of fluoxetine may, after a while, improve your sex life as your mood lifts and you become interested in life and relationships again.
Some of the possible negative effects include:
- men might get painful erections, problems with getting an erection and problems with ejaculating
- women might have some vaginal bleeding and might not reach orgasm the same way as before
- you may have a lower sex drive
Sexual side effects usually pass after the first couple of weeks. However, very rarely, they can be long lasting and may not get better even after stopping the medicine.
If these happen and are a problem for you, go back to your doctor to see if there's another treatment you can try.
Will I gain or lose weight?
Fluoxetine can make you feel less hungry than usual, so you may lose weight when you start taking it.
If you start to have problems with your weight while taking fluoxetine, talk to your doctor or pharmacist.
Can I drive or ride a bike?
Some people can't concentrate properly while they're taking fluoxetine. It might be best to stop driving and cycling for the first few days of treatment until you know how this medicine makes you feel.
Can I drink alcohol with it?
You can drink alcohol while taking fluoxetine but it may make you feel sleepy. It might be best to stop drinking alcohol for the first few days of treatment until you see how the medicine affects you.
Is there any food or drink I need to avoid?
You can eat and drink normally while taking fluoxetine.
Are there other treatments that will help?
Antidepressants, including fluoxetine, are just one of several approaches to treating depression. Other potential treatments include:
- talking therapy (such as cognitive behavioural therapy)
- exercise programmes
- help to get a good night's sleep
Choosing a treatment that's most suitable for you depends on:
- how long you've had depression
- your symptoms
- whether you've had any previous periods of depression
- whether previous treatment has worked
- how likely you are to stick with your treatment
- the potential side effects
- your preferences and priorities
Will recreational drugs affect it?
Cannabis with fluoxetine can give you a fast heartbeat. Cannabis can also make drowsiness worse with fluoxetine, especially in people who have just started taking it.
Methadone can increase the risk of side effects in people taking fluoxetine. It can be potentially dangerous to take fluoxetine with:
- stimulants like ecstasy (MDMA) or cocaine
- hallucinogens like LSD
- novel psychoactive substances (which used to be known as legal highs) like mephedrone
Fluoxetine hasn't been properly tested with recreational drugs. Talk to your doctor if you think you might use recreational drugs while taking fluoxetine.