Fluoxetine (Prozac)

NHS Choices

About fluoxetine

Fluoxetine is a type of antidepressant known as an SSRI (selective serotonin reuptake inhibitor).

It is often used to treat depression, and also sometimes obsessive compulsive disorder and bulimia.

Fluoxetine helps many people recover from depression, and it has fewer unwanted effects than older antidepressants.

Fluoxetine is available only on prescription. It comes as tablets and capsules.

Key facts

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.
Fluoxetine can affect an unborn baby. Tell your doctor straight away if you're trying to get pregnant or become pregnant while taking it.
Fluoxetine can cause withdrawal symptoms. Don't stop taking it without talking to your doctor.
Fluoxetine is called by the brand name Prozac.

Who can and can't take fluoxetine

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 - fluoxetine is not usually recommended in pregnancy or while breastfeeding
have an eye problem called glaucoma because fluoxetine can increase the pressure in your eye

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.

How and when to take it

Take fluoxetine once a day. It doesn't upset the stomach so 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 will I 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?

Ask your doctor for advice straight away. An overdose can lead to potentially serious symptoms such as:

vomiting
shaking
feeling sleepy
agitation
heart problems
lung problems
seizures

Side effects

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)
headaches
being unable to sleep
diarrhoea
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.

Tell a doctor straight away if you get:

headache, 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
chest pain or pressure, or shortness of breath
severe dizziness or passing out
fits, feelings of euphoria, excessive enthusiasm or excitement, or a feeling of restlessness that means you can't sit or stand still
putting on or losing weight without trying to
changes in your periods such as heavy bleeding, spotting, or bleeding between periods
painful erections that last longer than 4 hours - this may happen even when you are not having sex

Or, if you get any signs of abnormal bleeding including:

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
any bleeding that is very bad or that you cannot stop

Serious allergic reaction

In rare cases, it’s possible to have a serious allergic reaction to fluoxetine.

A serious allergic reaction is an emergency. Contact a doctor straight away if you think you or someone around you is having a serious allergic reaction.

The warning signs of a serious allergic reaction are:

getting a skin rash that may include itchy, red, swollen, blistered or peeling skin
wheezing
tightness in the chest or throat
having trouble breathing or talking
swelling of the mouth, face, lips, tongue, or throat

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.

How to cope with side effects

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.
being unable to sleep - take fluoxetine first thing in the morning
diarrhoea - drink plenty of water or other fluids. It may also help to take oral rehydration solutions you can buy from a pharmacy to prevent dehydration. Don't take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor

Pregnancy and breastfeeding

Fluoxetine is generally not recommended in pregnancy or while breastfeeding.

No antidepressants are considered completely safe to take in pregnancy or while breastfeeding. Your doctor will only want to prescribe fluoxetine when the benefits of taking the medicine outweigh the risks.

Fluoxetine and similar antidepressants have been linked with a small risk of problems for the unborn baby when they're taken in early or late pregnancy.

Fluoxetine and breastfeeding

Fluoxetine is not usually recommended if you're breastfeeding. Fluoxetine passes into breast milk and has been linked with side effects in breastfed babies.

Tell your doctor if you're trying to get pregnant, are already pregnant or if you're breastfeeding.

Cautions with other medicines

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 the herbal remedy, St John's wort, 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.

Common questions

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.

Don't 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?

Fluoxetine is safe to take for a long time. There don't seem to be any lasting harmful effects from taking it for many months and years.

However, taking fluoxetine for more than a year has been linked to a small increased risk of getting diabetes. But you will be regularly checked for this.

What will happen if I come off fluoxetine?

If you stop taking fluoxetine suddenly you may get unpleasant withdrawal symptoms. These include:

dizziness
feeling sick
numbness or tingling in the hands or feet
trouble sleeping
feeling agitated or anxious
headaches
shaking

Withdrawal symptoms are usually harmless and over within a few days but it's possible to prevent them by reducing the dose gradually when you stop taking this medicine.

Don't stop taking fluoxetine unless your doctor tells you to.

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?

Fluoxetine does not affect any type of contraception including contraceptive pills or the morning after pill.

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 should pass after the first couple of weeks. If they don't, and this causes a problem for you, go back to your doctor to see if there's an another antidepressant for you to 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.

Will recreational drugs affect it?

The sleep-inducing effects of cannabis can add to those of fluoxetine, especially in people who have just started taking it. Cannabis and fluoxetine can also give you a fast heartbeat.

Methadone can increase the risk of side effects in people taking fluoxetine.

It can be potentially dangerous to take fluoxetine with:

stimulants like MDMA (ecstasy) 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.

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 bouts of depression, whether previous treatment has worked, how likely you are to stick with your treatment, the potential side effects and your preferences and priorities.