Fluoxetine

Selective serotonin reuptake inhibitors

ATC code: N06AB03 (Fluoxetine)

Mechanism of action

Selectively blocks serotonin reuptake at the presynaptic membrane. Its distinguishing feature is a long half-life: 1-4 days for fluoxetine itself and 7-15 days for the active metabolite norfluoxetine. A missed dose therefore barely affects plasma levels, and withdrawal syndrome on discontinuation is less common than with other SSRIs.

Indications

Major depressive disorder

First line

First-line treatment for major depressive disorder in adults. Efficacy confirmed in numerous RCTs and meta-analyses. Starting dose is 20 mg daily; therapeutic effect develops over 2-4 weeks. The long half-life allows once-daily dosing. Side-effect profile is comparable to sertraline.

Sources

Obsessive-compulsive disorder

First line

First-line OCD treatment. Doses above the antidepressant range are usually needed – 40-80 mg daily. Response develops more slowly than in depression: efficacy should be assessed no earlier than 8-12 weeks at an adequate dose.

Sources

Bulimia nervosa

First line

The only SSRI with approval for bulimia nervosa. Recommended dose is 60 mg daily, higher than the standard antidepressant dose. In RCTs, fluoxetine reduced binge-purge episode frequency by 50-67% versus placebo. The effect is independent of comorbid depression.

Sources

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Stress and anxiety

Not recommended

Fluoxetine (Prozac) is an SSRI antidepressant. It is prescribed for depression, anxiety disorders, OCD, bulimia, and PMDD ( 2022 and NG222 guidelines). For energy, weight loss, or productivity in people without a psychiatric diagnosis, fluoxetine does not work: no clinical studies of such use exist. The 1990s Prozac marketing campaigns created the myth of a happiness pill, but no evidence base supports it. The drug has serious risks: sexual dysfunction (often persistent after discontinuation), hyponatremia, nausea, headache, and increased suicide risk in young adults under 24 ( boxed warning). If fluoxetine was prescribed for energy or weight loss, consider seeking a second opinion.

Sources

Practical notes

Timing and administration

Take once daily in the morning, with or without food. Morning dosing is preferred because of the activating effect – evening doses can disturb sleep. For bulimia the dose is 60 mg; for OCD it is titrated to 40-80 mg. If a dose is missed, the long half-life prevents critical concentration drops.

Special situations

The long half-life is a double-edged sword. Advantage: minimal withdrawal syndrome and missed-dose resilience. Disadvantage: drug interactions persist 5-6 weeks after discontinuation. Fluoxetine is a potent CYP2D6 inhibitor. When switching to another antidepressant, a washout period is required. MAOIs must not be combined – a minimum 5-week gap is needed.

Drug–drug interactions

24 pairs found. Sorted from critical to minor.

Critical

Linezolid

Oxazolidinone antibiotic

Mechanism

Fluoxetine (SSRI) raises synaptic serotonin. Linezolid reversibly inhibits MAO. The pair is notable because fluoxetine's active metabolite, norfluoxetine, persists for up to 5 weeks – the serotonergic effect outlasts dosing.

Symptoms

Serotonin syndrome: agitation, confusion, tremor, myoclonus, hyperreflexia, dilated pupils. Autonomic features: profuse sweating, tachycardia, hypertension, fever above 38.5 °C. Severe cases progress to seizures, rhabdomyolysis, disseminated intravascular coagulation, and death. First signs appear within hours of concurrent dosing.

Management

The combination is not prescribed. Stop fluoxetine at least 5 weeks before planned linezolid. For acute antibiotic need, use vancomycin or daptomycin. If linezolid is still required, monitor for serotonin syndrome during therapy plus 5 weeks after fluoxetine discontinuation.

Sources

Mechanism of action

Indications

Practical notes

Timing and administration

Special situations

Drug–drug interactions

Check interaction with another drug

Official sources

Safety

Contraindications

Serious adverse effects

Common adverse effects

PregnancyFDA C

Frequently asked

Mechanism of action

Indications

Practical notes

Timing and administration

Special situations

Drug–drug interactions

Check interaction with another drug

Official sources

Safety

Contraindications

Serious adverse effects

Common adverse effects

PregnancyFDA C

Frequently asked