Fluoxetine

Sounds like 'floo-OX-e-teen'

Easy-to-read medicine information about fluoxetine – what it is, how to take fluoxetine safely and possible side effects.

Type of medicine Also called
  • Antidepressant
  • Belongs to a group of medicines known as selective serotonin reuptake inhibitors (SSRIs)
  • Arrow-Fluoxetine®
  • Prozac®

What is fluoxetine?

Fluoxetine is used to treat depression, obsessive-compulsive disorder or eating disorders. It belongs to a group of medicines called selective serotonin reuptake inhibitors (SSRIs). It is believed that SSRIs work by increasing the activity of certain chemicals working in our brains called neurotransmitters. These pass signals from one brain cell to another. Although we don’t know for certain, the neurotransmitters that are most likely to be involved in depression and some other conditions are thought to be serotonin and noradrenaline. Selective serotonin reuptake inhibitors (SSRIs) are the most frequently prescribed antidepressants. SSRIs are called selective because they only affect serotonin.

In New Zealand, fluoxetine is available as capsules, tablets and a liquid. 

Read more about antidepressants and SSRIs

Dose

  • The dose of fluoxetine will be different for different people.
  • Your doctor may start you on a low dose and if you need to, will increase your dose slowly after a few weeks. This allows your body to get used to the medicine and reduces side effects.
  • Always take your fluoxetine exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much fluoxetine to take, how often to take it, and any special instructions. 

How to take fluoxetine

  • Fluoxetine is best taken in the morning. Take your dose at the same time each day.
  • If you are taking capsules, swallow with a glass of water. Do not open or chew.
  • If you have problems swallowing capsules, let your doctor know as you could be prescribed dispersible tablets which are dissolved in water and then swallowed. 
  • You can take fluoxetine with or without food but if you think it is upsetting your stomach, try taking it with food. 
  • If you forget to take your dose, take it if you remember soon after it is due, but if it nearly time for your next dose, just take it then. Do not take double the dose.
  • Keep taking fluoxetine every day. It may take 4 to 6 weeks before you notice the full benefits.
  • If you think fluoxetine is not working for you, do not stop taking it suddenly; speak to your doctor or nurse before stopping. 

Read more about what to expect when starting SSRIs – see SSRIs and frequently asked questions (FAQs) about SSRIs.

Precautions – before starting fluoxetine

  • Do you have any heart problems such as irregular heartbeat?
  • Have you had problems with mania or psychosis?
  • Do you have problems with your kidneys or liver?
  • Do you have epilepsy?
  • Do you have diabetes?
  • Are you pregnant or breastfeeding?
  • Do you have a bleeding disorder or stomach ulcer?
  • Are you taking any other medicines, including medicines you can buy without a prescription, such as herbal and complementary medicines or pain relief medicines?

If so, it’s important that you tell your doctor or pharmacist before you start fluoxetine. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Precautions – while taking fluoxetine

  • Alcohol: avoid alcohol while you are taking fluoxetine, especially when you first start treatment. Drinking alcohol while taking SSRIs can cause drowsiness and affect concentration, putting you at risk of falls and other accidents. It can also cause agitation, aggression and forgetfulness. If you do drink alcohol, drink only small amounts and see how you feel. Do not stop taking your medication.
  • Diabetes: if you have diabetes, you may need to check your blood glucose more often because fluoxetine can affect the levels of glucose in your blood.

Possible side effects

Like all medicines, fluoxetine can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Suicidal behaviour

The use of antidepressants has been linked with an increase in suicidal thoughts and behaviour. Children, teenagers, young adults and people with a history of suicidal behaviour are particularly at risk. This is most likely during the first few weeks of starting an antidepressant or if the dose is changed. It is important to look for signs of suicidal behaviour such as agitation or aggression and ask about suicidal thoughts, self-harm, worsening of low mood, If you notice any of these signs, contact your doctor immediately.
It is ok and important to ask about suicidal thoughts and this will not increase risk. 

If you need urgent help or are concerned, phone:

  • Lifeline 0800 543 354 (available 24/7), or
  • Healthline 0800 611 116, who can give you the phone number for your local mental health crisis line.

Risk of bleeding

SSRIs can increase your risk of bleeding especially if taken with NSAIDs (non-steroidal anti-inflammatory drugs) such as diclofenac and ibuprofen. Check with your doctor or pharmacist before you take pain relief.

Sexual side effects

SSRIs in both men and women can cause reduced sexual drive, lack of libido and problems keeping an erection and reduce the intensity of organism. It’s important to talk to your healthcare provider if you get these effects, as they can be difficult to deal with and may not go away. Your healthcare provider may be able to suggest treatment or may reduce the dose of the SSRI or change to a different one.

Other side effects

Side effects What should I do?
  • Feeling sick (nausea) or vomiting
  • Stomach upset
  • This is quite common when you first start fluoxetine
  • Try taking your dose with food
  • Tell your doctor if troublesome
  • Difficulty falling asleep
  • Try taking fluoxetine in the morning
  • Tell your doctor if troublesome
  • Feeling sleepy, drowsy, dizzy or tired
  • Be careful when driving or using tools until you know how this medicine affects you
  • Tell your doctor or pharmacist if troublesome
  • Feeling anxious or nervous
  • Increased sweating
  • Dry mouth
  • These are quite common when you first start taking fluoxetine and may go away with time
  • Tell your doctor or pharmacist if troublesome
  • Loss of sex drive or libido
  • Tell your doctor
  • Suicidal thoughts, thoughts of harming yourself, or worsening depression
  • Tell your doctor or pharmacist immediately or ring HealthLine 0800 611 116
  • Signs of serotonin syndrome such as feeling agitated and restless, heavy sweating, shivering, fast heart rate or irregular heartbeat, headache, diarrhoea and rigid or twitching muscles
  • You are at increased risk of serotonin syndrome if you recently started
    taking fluoxetine or recently increased the dose or started other medicines that can cause serotonin syndrome 
  • Tell your doctor or pharmacist immediately or ring HealthLine 0800 611 116

Interactions

Fluoxetine interacts with many other medications (including pain relief medicines) and herbal supplements (such as St. John's Wort) so check with your doctor or pharmacist before starting fluoxetine or before starting any new medicines.

Learn more

The following links provide more information on fluoxetine.

Medsafe Consumer Information Sheet: Prozac 
New Zealand Formulary Patient Information: Fluoxetine

References

  1. Fluoxetine New Zealand Formulary
  2. Selective serotonin re-uptake inhibitors New Zealand Formulary
  3. The role of medicines in the management of depression in primary care BPAC, 2017
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 14 Feb 2018