Fluoxetine – Long-acting SSRI antidepressant for depression and anxiety.
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What is Fluoxetine?
Fluoxetine (Prozac) is one of the most well-known and extensively studied SSRI antidepressants. Its long half-life and proven effectiveness across multiple mental health conditions make it a popular choice for treating depression, anxiety disorders, and OCD.
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What is Fluoxetine used for?
- Major depressive disorder
- Generalised anxiety disorder
- Obsessive-compulsive disorder (OCD)
- Panic disorder
- Bulimia nervosa
- Premenstrual dysphoric disorder (PMDD)
- Post-traumatic stress disorder (PTSD)
How does Fluoxetine work?
A selective serotonin reuptake inhibitor (SSRI) with a long half-life that increases serotonin levels in the brain, helping to improve mood, reduce anxiety, and stabilize emotional responses.
Dosage and Administration
Adults
Starting dose 20mg daily, may be increased to 40-60mg daily. Maximum 80mg daily in some cases.
Children
10mg daily for children over 8 years (specialist supervision required).
Important Notes
- Take at the same time each day, preferably in the morning.
- Can be taken with or without food.
- May take 4-6 weeks to feel full benefits.
- Longer half-life means less withdrawal symptoms if missed doses.
Side Effects
Common Side Effects
- Nausea and stomach upset
- Insomnia and sleep disturbances
- Headache
- Nervousness and anxiety (initially)
- Sexual side effects
- Drowsiness or fatigue
- Dry mouth
- Increased sweating
Serious Side Effects
Seek immediate medical attention if you experience:
- Thoughts of self-harm or suicide (especially when starting)
- Serotonin syndrome (confusion, rapid heart rate, fever)
- Severe allergic reactions
- Abnormal bleeding
- Low sodium levels (hyponatraemia)
- Manic episodes in bipolar disorder
Important Warnings
- May initially increase thoughts of self-harm, especially in young adults—close monitoring required.
- Long half-life means effects persist for weeks after stopping.
- May trigger manic episodes in people with undiagnosed bipolar disorder.
- Tell your GP if you have heart problems, epilepsy, or bleeding disorders.
- Can interact with many medications due to enzyme inhibition.
Drug Interactions
Tell your GP if you're taking any of the following medications:
- MAOIs—dangerous interaction, must avoid completely.
- Other antidepressants—risk of serotonin syndrome.
- Warfarin and blood thinners—increased bleeding risk.
- Tramadol and some painkillers—risk of serotonin syndrome.
- Many medications metabolized by liver enzymes—levels may be increased.
- St John's Wort—avoid this herbal supplement.
Frequently Asked Questions
Why is Fluoxetine often chosen as a first-line antidepressant?
Fluoxetine has a long half-life, which means fewer withdrawal symptoms, and extensive research showing effectiveness for multiple conditions including depression and anxiety.
What makes Fluoxetine different from other SSRIs?
Its very long half-life (1-3 days vs 1 day for others) means more stable blood levels and easier withdrawal if stopping treatment.
Can Fluoxetine cause weight changes?
Initial treatment may cause slight weight loss, but long-term use can lead to weight gain in some people. Effects vary significantly between individuals.
Is it safe to take during pregnancy?
Fluoxetine is generally considered one of the safer SSRIs in pregnancy, but this decision should always be made with specialist guidance weighing risks and benefits.
Medically Reviewed by: Mohammed Hassan - Independent Prescriber
Last Updated: 2025-01-14