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SSRI (Selective Serotonin Reuptake Inhibitor)

Fluoxetine

Brand names: Prozac

Used in: Depression & Anxiety

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) used for depression, obsessive-compulsive disorder and bulimia. It has a long half-life.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Indication Adult Pediatric MDD ( 2.1 ) 20 mg/day in am (initial dose) 10 to 20 mg/day (initial dose) OCD ( 2.2 ) 20 mg/day in am (initial dose) 10 mg/day (initial dose) Bulimia Nervosa ( 2.3 ) 60 mg/day in am Panic Disorder ( 2.4 ) 10 mg/day (initial dose) Depressive Episodes Associated with Bipolar I Disorder ( 2.5 ) Oral in combination with olanzapine: 5 mg of oral olanzapine and 20 mg of fluoxetine once daily (initial dose) Oral in combination with olanzapine: 2.5 mg of oral olanzapine and 20 mg of fluoxetine once daily (initial dose) A lower or less frequent dosage should be used in patients with hepatic impairment, the elderly, and for patients with concurrent disease or on multiple …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2019-02-01. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

It selectively inhibits serotonin reuptake, increasing synaptic serotonin over several weeks.

Prescribing in practice

  • The long half-life means slow onset and offset, fewer discontinuation symptoms, but prolonged potential for interactions.
  • Initiation can transiently worsen anxiety; be alert to serotonin syndrome with other serotonergic drugs and to increased bleeding risk with NSAIDs/antithrombotics.
  • It is the SSRI with the best evidence in children and young people, where indicated.

Monitoring

Review mood, anxiety and suicidal ideation early after starting and at dose changes, particularly in younger patients.

Counselling the patient

  • It can take a few weeks to work, and anxiety may briefly increase at first.
  • Report worsening mood or thoughts of self-harm.
  • Discontinuation effects are usually mild because it is long-acting.

Evidence & guidelines

A first-line SSRI for depression (NICE NG222) and the preferred antidepressant in young people where drug treatment is indicated.

Reference: NICE CG90; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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