An SSRI antidepressant (Prozac)
Fluoxetine
A long-acting SSRI antidepressant for depression and anxiety, and the SSRI most used in younger people under specialist care.
What is Fluoxetine?
Fluoxetine — best known by the brand name Prozac — is a widely used selective serotonin reuptake inhibitor (SSRI) antidepressant. It is used for depression, obsessive-compulsive disorder and bulimia, and is the SSRI most often chosen for young people.
Education and reference only. This is a plain-language guide to Fluoxetine — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Fluoxetine — perhaps best known by the brand name Prozac — is a widely used SSRI (selective serotonin reuptake inhibitor) antidepressant. It is used for depression and various anxiety conditions, and is the SSRI most often chosen for children and younger people, where it is started under specialist guidance. Its defining feature is that it is long-acting: it and its active breakdown product stay in the body for a long time after each dose, which shapes how it behaves when doses are missed or when it is stopped.
How it works
Fluoxetine increases the amount of serotonin — a chemical messenger linked to mood — available between nerve cells in the brain by blocking its reabsorption ("reuptake") back into the nerve that released it. With more serotonin staying active in the gaps between nerves, mood gradually lifts and anxiety eases over a number of weeks. Because fluoxetine lingers in the body, the level falls only slowly when it is stopped — which is why it causes fewer withdrawal symptoms, but also why interactions can persist for some time after the last dose.
Company & origin
Originated / developed by: Eli Lilly.
Fluoxetine was the first widely used SSRI, discovered by Eli Lilly scientists (including David Wong and Bryan Molloy) in the United States in the 1970s. It was approved by the FDA in 1987 and launched as Prozac, transforming the treatment of depression.
What it treats
Conditions Fluoxetine is used for
Practical use
How to take Fluoxetine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Usually taken once a day; because it can be activating, the morning is often preferred.
- Swallow the capsule or tablet with water, with or without food; a liquid form is available.
- It can take several weeks to work, so persistence is important.
- If you miss a dose, skip it and take the next one as usual — do not double up.
- Because it stays in the body for a long time, withdrawal symptoms are usually milder, but you should still stop under medical guidance.
- Tell your doctor if your mood worsens or you have distressing thoughts, especially early on.
Weighing it up
Advantages & disadvantages of Fluoxetine
Advantages
- Long-acting, so occasional missed doses matter less and withdrawal tends to be gentler.
- Strong evidence base and often the SSRI of choice in young people.
- Once-daily dosing.
- Cheap, widely available generic.
Disadvantages
- Its long action means interactions can persist for weeks after stopping.
- Can cause nausea, restlessness, sleep changes and sexual side effects.
- May take several weeks to take full effect.
- Mood or anxiety can briefly worsen when first starting, like other antidepressants.
Practical use
Good to know
It is taken once a day and, like all antidepressants, takes several weeks to reach full effect. Because it is long-acting, a missed dose matters less than with shorter-acting SSRIs, and stopping tends to cause fewer discontinuation symptoms — but its effects, and its potential to interact with other medicines, can carry on for some weeks after the last tablet. Some people feel more activated, restless or anxious in the early weeks; this usually settles. It must not be combined with, or started too soon after, an MAOI antidepressant.
Who should not take it / use with caution
- People taking, or who have recently taken, an MAOI antidepressant — these must not be combined, and because fluoxetine is long-acting a longer gap is needed when switching to or from it.
- Used with caution in people with a history of bleeding problems, epilepsy, certain heart conditions, low blood sodium, or who are pregnant or breastfeeding — assessed individually.
- In children and younger people it is started and supervised by a specialist, with close monitoring of mood.
Monitoring
- Mood, anxiety and any thoughts of self-harm, especially in the early weeks, after dose changes, and (in younger people) under specialist review
- Blood sodium in those at risk
- Tolerability and any signs of increased agitation
Side effects
- Nausea, headache, disturbed sleep, sweating or reduced appetite, especially in the first weeks; feeling more activated, restless or anxious early on, which usually settles.
- Sexual side effects (such as reduced desire), which can persist while taking it.
- Less commonly, a low blood sodium level, changes in mood or, if combined with other serotonin medicines, serotonin syndrome — which needs urgent attention.
Key interactions
- MAOI antidepressants must not be combined with fluoxetine, and its long-acting nature means a wash-out period is needed when switching.
- Other serotonin-raising medicines (some antidepressants, tramadol, triptans for migraine, St John's Wort) increase the risk of serotonin syndrome.
- NSAID painkillers, aspirin and anticoagulants increase bleeding risk; fluoxetine can also affect the levels of certain other medicines, an effect that can persist after stopping.
Available as: Capsules, tablets and a liquid for those who prefer or cannot swallow capsules.
Answers
Fluoxetine: frequently asked questions
Why is fluoxetine said to be easier to stop than other antidepressants?
Fluoxetine stays in the body for a long time after the last dose, so its level falls slowly rather than dropping suddenly. This gradual "self-tapering" means it generally causes fewer discontinuation symptoms than shorter-acting SSRIs — although stopping any antidepressant should still be discussed with your prescriber.
How long does fluoxetine take to work?
It usually takes a few weeks before the full benefit is felt, and some early improvement may come before your mood lifts. Keep in touch with your prescriber and persevere rather than stopping early if it does not seem to help straight away.
Why is fluoxetine the SSRI used in children and teenagers?
Fluoxetine has the most evidence supporting its use in younger people, so when an antidepressant is needed it is usually the first choice — always started and supervised by a specialist, with close monitoring of mood and any thoughts of self-harm.
I feel more restless and anxious after starting it — is that normal?
Yes, fluoxetine can feel "activating" in the early weeks, causing restlessness, jitteriness or more anxiety that usually settles as your body adjusts. Tell your prescriber if it is severe, or if you have any thoughts of self-harm, as you should be reviewed.
Is Prozac the same as fluoxetine?
Yes — fluoxetine is the generic (active-ingredient) name and Prozac is a brand name. Generic fluoxetine contains the identical active ingredient.
The wider class
About SSRIs
Fluoxetine belongs to the ssris class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF: Fluoxetine.
- electronic Medicines Compendium (SmPC): Fluoxetine (Prozac).
- NICE CKS: Fluoxetine.
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