Fluoxetine (Prozac)

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 as tablets and capsules.

  1. Key facts

    • It usually takes 4 to 6 weeks for fluoxetine to work.
    • Common side effects include feeling sick, 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.
  2. Who can take fluoxetine

    Fluoxetine can be taken by adults for depression, obsessive compulsive disorder and bulimia.

    Fluoxetine can be taken by children aged 8 or older for depression.

    Check with your doctor before starting to take fluoxetine if you:

    • have an allergy to fluoxetine or any of its ingredients
    • 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

    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.

  3. How and when to take

    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.

    The usual dose of fluoxetine is 20mg a day in adults. However, it may be started at a lower dose then 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 often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways that are suitable for you and your medicines.

    What if I take too much?

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

    • vomiting
    • shaking
    • feeling sleepy
    • agitation
    • heart problems
    • lung problems
    • seizures
  4. Side effects

    Like all medicines, fluoxetine can cause side effects in some people, but many people have no side effects or only minor ones.

    Common side effects

    These side effects happen in more than 1 in 100 people. If you experience these side effects, keep taking the medicine, but tell your doctor if they bother you or don't go away:

    • feeling sick
    • 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 develop:

    • low sodium levels – warning signs include headache, trouble focusing, memory problems, not thinking clearly, weakness, seizures, or losing your balance
    • 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:

    • bleeding from the gut – warning signs include vomiting blood or dark vomit, coughing up blood, blood in your pee, black or red poo
    • 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

    It's rare to have an allergic reaction to fluoxetine but if this happens to you, stop taking the medicine and contact a doctor straight away.

    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 medicine packet.

  5. How to cope with side effects

    Some of the common side effects of fluoxetine will gradually improve as your body gets used to it. 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 – 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

    You can report any suspected side effect to a UK safety scheme. 

  6. 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 passes into breast milk and has been linked with side effects in breastfed babies.

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

  7. 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 and supplements.

  8. Common questions