Fluoxetine

Sounds like 'floo-OX-e-teen'

Fluoxetine is used to treat depression, bulimia nervosa and obsessive-compulsive disorder. Find out how to take it safely and possible side effects. Fluoxetine is also called Fluox or Prozac.

If you need help or want to talk to somebody about your mental health, you can get support from any of the following:

  • Free call or text 1737 any time for support from a trained counsellor
  • Lifeline 0800 543 354 (0800 LIFELINE) or free text 4357 (HELP)
  • Suicide Crisis Helpline 0508 828 865 (0508 TAUTOKO)
  • Healthline 0800 611 116
  • Samaritans 0800 726 666.

What is fluoxetine?

Fluoxetine is a type of antidepressant known as a selective serotonin reuptake inhibitor (SSRI)Fluoxetine is used to treat depressionobsessive-compulsive disorder (OCD) or eating disorders such as bulimia nervosa and premenstrual dysphoric disorder. We don't know for certain, but researchers think that SSRIs work by increasing the activity of serotonin which is thought to improve mood, emotion and sleep. Read more about SSRIs.

Dose

In Aotearoa New Zealand fluoxetine is available as capsules (20 mg) or dispersible tablets (20 mg).

  • The dose of fluoxetine will be different for different people and depends on the condition being treated.
  • Your doctor will usually start you on a low dose and if necessary will increase your dose slowly after a few weeks. This allows your body to get used to the medicine and reduces the chance of 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

Capsules: Swallow the capsule whole with a glass of water.

Tablets: The tablets can either be swallowed with a glass of water or dissolved in water. To dissolve, place the tablet(s) in about 100mL (½ glass) of water, swirl until it dissolves, then drink immediately.

  • Timing: Fluoxetine is best taken in the morning. Take your dose at the same time each day. 
  • Food: You can take fluoxetine with or without food but if you think it is upsetting your stomach, try taking it with food. 
  • Missed dose: If you forget to take your dose, take it as soon as you remember. But if it is nearly time for your next dose, just take it at the right time. Don't take double the dose.
  • Keep taking fluoxetine every day. It may take 4 to 6 weeks before you notice the full benefits of fluoxetine and you should start to feel better after 1 to 2 weeks.  Some people notice side effects in the first few weeks before they start to feel better. Fluoxetine is often needed for at least a few months. Your doctor will discuss with you how long to take it for; this depends on what you are taking it for, and how well it is working.
  • If you think fluoxetine is not working for you. Don't stop taking it suddenly; talk to your doctor or nurse before stopping. It is usually best to stop taking fluoxetine very slowly to avoid side effects.

Things to consider while you are taking fluoxetine

  • Limit alcohol intake as it can increase your chance of side effects such as drowsiness and reduced concentration.
  • Avoid driving and doing other tasks where you need to be alert until you know how this medicine affects you.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
  • Fluoxetine can interact with some other medicines (including anticoagulants and anti-inflammatories, eg, ibuprofen), herbal supplements (eg, St John's Wort), and recreational drugs, so check with your doctor or pharmacist before starting fluoxetine and before starting any new products.
  • 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 of fluoxetine

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.

Side effects What should I do?
  • Nausea (feeling sick)
  • Vomiting (being sick)
  • Headache
  • Dry mouth
  • Increased sweating
  • Diarrhoea (runny poos/hamuti)
  • This is quite common when you first start fluoxetine.
  • If you have nausea, try taking your dose with food.
  • Tell your doctor if they bother you.
  • Difficulty falling asleep
  • This is quite common. Try taking your dose in the morning.
  • Feeling sleepy, drowsy, dizzy or tired
  • Difficulty concentrating
  • These are quite common. 
  • Try taking your dose in the evening
  • Be careful when driving or using tools until you know how this medicine affects you.
  • Avoid drinking alcohol. Read more about how alcohol affects medicines.
  • Feeling less or more hungry than usual
  • Changes in weight (increase or decrease)
  • Tell your doctor if they cause you problems.
  • Loss of sex drive or libido
  • Changes in periods (menstruation)
  • Signs of low sodium such as dizziness, confusion, agitation, cramps, unsteadiness, feeling faint or tired.
  • This is most common in older people, women, people who are also taking diuretics (water tablets) or omeprazole and people with low body weight.
  • Let your doctor know if you get these symptoms.
  • Agitation, aggression, worsening of low mood, thoughts self-harm.
  • These are rare but serious side effects
  • They are most likely to happen during the start of treatment or when doses are changed.
  • Contact your doctor immediately.
  • For urgent help contact Healthline 0800 611 116 or Lifeline 0800 543 354 (available 24/7).
  • 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.
  • These are rare but serious side effects.
  • You are at increased risk of serotonin syndrome if you just started taking the SSRI, increased the dose or started other medicines that can cause serotonin syndrome.
  • Tell your doctor immediately or ring Healthline 0800 611 116.
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product.

Learn more

The following links provide more information on fluoxetine.

Fluoxetine Patient Information (Māori) NZ Formulary, NZ
Fluoc Medsafe Consumer Information Sheet, NZ

References

  1. Fluoxetine NZ Formulary, NZ, 2022
  2. Selective serotonin re-uptake inhibitors NZ Formulary, NZ, 2022
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 18 Oct 2022