HeadMeds gives young people in the United Kingdom general information about medication. HeadMeds does not give you medical advice. Please talk to your Doctor or anyone else who is supporting you about your own situation because everyone is different. Please read more important details about our site.

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Fluoxetine

Return to Fluoxetine overview
  1. Use and Action
  2. Warnings and side effects
  3. Sex, drink, weight and everything else
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Taking Prozac, Citalopram and Amitriptyline
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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. If you think you might be getting a side effect from fluoxetine, then you should discuss this with your doctor, nurse, or pharmacist.

If you have any thoughts of suicide, or of other ways of hurting yourself, go straight to a hospital with your medicine.

This may be a side-effect, and you need urgent help.

  • When taking fluoxetine or another antidepressant, some people think about hurting themselves or have suicidal thoughts. This is more common at the start of treatment than later on.
  • This can happen to anyone, but is more likely to happen if you are less than 25 years old. Fluoxetine is considered to be safer than other antidepressants for people under the age of 18.
  • You must go straight to hospital if you have thoughts of hurting yourself or have suicidal thoughts. Take your medicines with you and tell the doctor that you are taking fluoxetine.

Fluoxetine has possible side effects, and some of these are rare but serious

  • Go to a doctor or hospital straight away and stop taking your fluoxetine if you get the following symptoms:
  • Shivering, excessive sweating, restlessness, irritability, agitation, confusion, mood changes, high temperature (fever), fast heartbeat, diarrhoea, trembling, weird muscle movements (that you cannot control), overactive reflexes, or losing consciousness. These may be symptoms of a rare but serious condition called ‘serotonin syndrome’.
  • Tiredness, confusion, headache, irritability, feeling or being sick (nausea and vomiting), and muscle twitching. These can be symptoms of a low blood level of sodium, but some of these are also symptoms of serotonin syndrome.
  • 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.
  • Difficulty breathing, swelling of your face or throat, and itching skin lumps. These may be symptoms of an allergic reaction.
  • Having fits (also known as convulsions or seizures).
  • Feeling very excited or ‘high’.
  • Go to a doctor or hospital straight away but do not stop taking your fluoxetine if you get the following symptoms:
  • Your behaviour changes because you feel irritated or agitated.
  • If you have an erection that is painful and lasts for a long time.

Some side-effects that do appear should get better after a few days. If they do not, you should go back to your doctor

Some side-effects of fluoxetine may – strangely - seem like other mental health symptoms. Some side-effects here are also the opposites of each other. The balance of chemicals in the brain is very fragile, and hard to control! If they do not get better after a few days on the fluoxetine, go back to the 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 (could affect more than 1 in 10 people)

  • Difficulty sleeping (insomnia)
  • headache and feeling tired
  • loose poo (diarrhoea)
  • feeling sick (nausea)

Common side effects (could affect up to 1 in 10 people)

  • not feeling hungry  
  • weight loss
  • nervousness, anxiety, restlessness, poor concentration, feeling tense     
  • decreased sex drive or sexual problems, including difficulty staying hard (keeping your erection)
  • 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
  • going to wee more often
  • unexplained vaginal bleeding

If you get any side effects not listed here please look at the patient leaflet in the medicine pack

  • 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 if 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

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.

Talk to your doctor or pharmacist if you are taking any other medicines

Always talk to the doctor if you are taking other medicines. Tell the pharmacist you are taking fluoxetine if you buy medicines (including things you put on your skin) for common illnesses.

Be careful if you are also using drugs

  • Cannabis can have uncertain effects with fluoxetine and so great care is needed.
  • 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 mood effects of cocaine.
  • Taking fluoxetine with cocaine or ecstasy or amphetamines 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.

Stopping this medicine quickly, or reducing the dose too much at once, may cause uncomfortable symptoms

  • Stopping fluoxetine suddenly can sometimes cause side effects, which are usually mild, but for a few people can be severe. Also, if you stop taking fluoxetine too soon, there is more chance that your mental health symptoms will come back.
  • Once you start taking a SSRI, the brain adjusts to having a new level of serotonin around. If you stop taking the SSRI all at once, the balance starts to change again. You could get some symptoms from the change.
  • Fluoxetine is less likely to cause withdrawal effects on stopping than other antidepressant medicines. This is because your body takes longer to get rid of it.
  • You can stop taking fluoxetine safely with your doctor’s help. 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 number of weeks to reduce the chance of withdrawal effects.
  • See your doctor if you want to stop fluoxetine or have problems after stopping it.
  • Fluoxetine and other antidepressants are not addictive. Although there can be withdrawal effects when they are stopped, you will not have cravings for or get ‘hooked’ on an antidepressant.
  • Some of the withdrawal effects you might get when fluoxetine is stopped include:
  • Flu-like symptoms such as chills, muscle aches, excessive sweating, headache, and feeling or being sick.
  • Feeling unusually tired or weak.
  • Sleep disturbances such as difficulty sleeping or vivid dreams.
  • Shock-like sensations.
  • Dizziness, especially when moving.
  • Feeling anxious, restless, irritable, or agitated.
  • Shaking.
  • Difficulty remembering things or concentrating on things.
  • These symptoms should stop after two weeks for most people, but some people can get them for a few months.

Reference sources

Search www.medicines.org.uk to find patient information leaflets and prescribing information on fluoxetine. Capsules and liquid are listed separately. The SmPC lists all the inactive ingredients in the product so you can check against any allergies. If you are still unsure about this then speak to your pharmacist.

  • British National Formulary (BNF) and British National Formulary for children. Download the BNF/BNFC app (blue background) on to your mobile device. No longer available for public access via the web 
  • Taylor D, Barnes T, Young A. Maudsley Prescribing Guidelines in Psychiatry, 13th edition. Oxford: John Wiley & Sons, May 2018. ISBN: 978-1-119-44260-8
  • Royal Pharmaceutical Society. Medicines Ethics and Practice (42nd edition). London: RPS, 2018. Standards for pharmacists to work to. It is not a free publication
  • World Anti Doping Agency WADA Prohibited List https://www.wada-ama.org/en/resources/science-medicine/prohibited-list-documents 
  • Choiceandmedication; an independent source of information on many mental health conditions and their medicines with easy to read fact sheets www.choiceandmedication.org Personal subscriptions to download the app available for £1 per month (with proportionate discounts for longer periods) but your local mental health Trust may subscribe and provide information sheets for free.
  • Best Use of Medicines in Pregnancy (BUMPS). Information sheets on drugs in pregnancy http://www.medicinesinpregnancy.org/ 
  • Drugs and Lactation Database (LactMed). Information on drugs in breastfeeding https://toxnet.nlm.nih.gov/newtoxnet/lactmed.htm 
Stop taking medsStop taking Fluoxetine and go to a doctor or hospital straight away if you get any of the following symptoms:

Go to a doctor or hospital straight away and stop taking your fluoxetine if you get the following symptoms:

  • Shivering, excessive sweating, restlessness, irritability, agitation, confusion, mood changes, high temperature (fever), fast heartbeat, diarrhoea, trembling, weird muscle movements (that you cannot control), overactive reflexes, or losing consciousness. These may be symptoms of a rare but serious condition called ‘serotonin syndrome’.
  • Tiredness, confusion, headache, irritability, feeling or being sick (nausea and vomiting), and muscle twitching. These can be symptoms of a low blood level of sodium, but some of these are also symptoms of serotonin syndrome.
  • 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.
  • Difficulty breathing, swelling of your face or throat, and itching skin lumps. These may be symptoms of an allergic reaction.
  • Having fits (also known as convulsions or seizures).
  • Feeling very excited or ‘high’.
Dont stop taking medsGo to your doctor or the hospital straight away, but don't stop taking Fluoxetine if you get any of the following symptoms:

Go to a doctor or hospital straight away but do not stop taking your fluoxetine if you get the following symptoms:

  • Your behaviour changes because you feel irritated or agitated.
  • For men, if you have an erection that is painful and lasts for a long time.

Some side-effects that do appear should get better after a few days. If they do not, you should go back to your doctor.

Don't stop taking Fluoxetine until you talk to your doctor or you may get withdrawal symptoms as well.

Very common - could affect more than 1 in 10 people

  • Difficulty sleeping (insomnia)
  • headache and feeling tired
  • loose poo (diarrhoea)
  • feeling sick (nausea)
  • Common - could affect up to 1 in 10 people

    • not feeling hungry
    • weight loss
    • nervousness, anxiety, restlessness, poor concentration, feeling tense
    • decreased sex drive or sexual problems, including difficulty staying hard (keeping your erection) in men to have sex
    • 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
    • going to wee more often
    • unexplained vaginal bleeding