Fluoxetine. What diseases does it treat?

Start dosing adults at 20 mg once daily; clinical improvement commonly appears within 2–4 weeks with additional gains through 6–12 weeks. For panic disorder and OCD, titrate slowly–many patients require 40–60 mg/day. Bulimia trials used 60 mg/day. In specialist care, some cases reach a maximum of 80 mg/day with close monitoring.

Watch for side effects such as nausea, insomnia, headache, sweating, tremor and sexual dysfunction. Fluoxetine and its primary metabolite have prolonged half-lives (fluoxetine ~2–4 days; norfluoxetine ~7–15 days), which reduces abrupt withdrawal symptoms but does not eliminate them. Expect variable weight effects: initial loss in some patients and possible weight gain with long-term use.

Do not combine fluoxetine with monoamine oxidase inhibitors (MAOIs). Wait at least 14 days after stopping an MAOI before starting fluoxetine, and wait at least 5 weeks after stopping fluoxetine before initiating an MAOI. Avoid concurrent use with other strong serotonergic agents without close supervision because of the risk of serotonin syndrome. Use caution with anticoagulants and NSAIDs due to increased bleeding risk and with drugs metabolized by CYP2D6 since fluoxetine is a potent inhibitor.

Screen before prescribing: assess for past or family history of bipolar disorder (antidepressants can trigger mania), check sodium in elderly or frail patients for hyponatremia, and consider baseline ECG if multiple QT-prolonging medications are present. For children and adolescents, fluoxetine is FDA-approved for major depressive disorder (ages 8+) and for obsessive-compulsive disorder (ages 7+); start at lower doses (for example, 10 mg) and titrate with frequent follow-up. Monitor all patients–especially those under 25–for new or increased suicidal thoughts or unusual behavioral changes during the first weeks and after dose adjustments.

Discuss pregnancy and breastfeeding openly: fluoxetine crosses the placenta and transfers into breast milk. Balance maternal mental-health needs against potential neonatal adaptation symptoms and consult obstetrics and pediatrics when making treatment decisions. Coordinate dose changes, review interacting medications, and schedule follow-ups within the first 1–3 months and after any dose modification.

Fluoxetine for Major Depressive Disorder: dosing, expected time to response, and switching considerations

Start adults at 20 mg orally once daily. Reassess after 4–6 weeks; if response is inadequate, increase to 40 mg daily. Further increases can be made to 60–80 mg/day for partial responders under close monitoring for side effects and drug interactions.

Pediatrics: For children and adolescents with MDD, begin at 10 mg once daily for one week, then increase to 20 mg daily. Dose escalation beyond 20 mg should involve specialist input and careful benefit–risk assessment.

Older adults and hepatic impairment: Begin at 10 mg daily and titrate slowly. Expect slower clearance; monitor sodium, bleeding risk, sedation, and gait. Consider lower target doses when multiple comorbidities or interacting medications exist.

Time course for clinical effects: Improvements in sleep, appetite, or energy may appear within 1–2 weeks. Look for meaningful reduction in core depressive symptoms by 4–6 weeks. If no meaningful change after 6–8 weeks at an adequate dose, treat as nonresponse. Allow 2–4 weeks after any upward titration before judging effect.

Pharmacokinetics that affect switching: Fluoxetine parent drug has an elimination half-life of roughly 1–4 days; its active metabolite norfluoxetine persists approximately 7–15 days. Expect steady state and prolonged washout (several weeks), which reduces withdrawal but increases interaction risk with newly started agents.

MAOI and washout rules: Do not start an MAOI until at least 5 weeks after stopping fluoxetine. If stopping an MAOI, wait 14 days before initiating fluoxetine.

Practical switching strategies: For most SSRIs/SNRIs, a direct switch (stop fluoxetine and start the new agent the next day) is often used because residual fluoxetine reduces discontinuation symptoms; nevertheless, monitor for additive serotonergic effects. When switching to drugs primarily metabolized by CYP2D6 (tricyclics, certain antipsychotics), begin the new agent at a reduced dose because fluoxetine inhibits CYP2D6 and can raise plasma concentrations. Avoid high combined doses with bupropion or other seizure‑risk agents.

When to change approach: If side effects are intolerable early, reduce dose or switch to an antidepressant with a shorter half-life and fewer CYP interactions. If nonresponse persists after ≥6–8 weeks at therapeutic dose, switch to a different class (SNRI, bupropion, mirtazapine) or add an evidence‑based augmentation (bupropion, atypical antipsychotic, lithium) while accounting for pharmacokinetic interactions and patient comorbidity; involve psychiatry for treatment‑resistant cases.

Fluoxetine in Obsessive-Compulsive Disorder: symptom targets and recommended treatment length

Begin fluoxetine at 20 mg once daily for adults with OCD; if symptoms remain after 4–6 weeks, increase to 40–60 mg/day (split dosing permitted). Continue an adequate dose for at least 12 weeks before labeling treatment nonresponsive.

Symptom targets and measurement

Use the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) to track progress. Define response as a ≥25–35% reduction in Y-BOCS score; aim for remission when Y-BOCS falls to ≤8. Track concrete functional changes: time spent on rituals (minutes per day), interference with work/school, and ability to resist compulsions. Reassess every 4–6 weeks during dose adjustments and every 8–12 weeks once stable.

Dosing strategy, expected time course and recommended duration

Expect partial improvement by 4–6 weeks and clearer benefit by 10–12 weeks; maximal response may require the full 12-week acute trial at an adequate dose. After response, continue the effective dose for a minimum of 6–12 months to reduce relapse risk. For patients with severe, recurrent, or early-onset OCD, plan maintenance for 1–3 years or longer based on relapse history and functional status. When stopping, taper gradually; fluoxetine’s long active metabolite lowers abrupt-withdrawal risk, but allow several weeks of dose reduction in most patients.

If minimal or no response after 12 weeks at ≥40 mg/day, consider one of the following: raise to 60 mg/day if tolerated, add evidence-based augmentation (low-dose antipsychotic such as risperidone or aripiprazole), switch to clomipramine or another SSRI, or prioritize/augment with structured exposure and response prevention (ERP). Monitor for emergent anxiety, activation, sleep disruption, and suicidal ideation, especially in adolescents and young adults; adjust strategy promptly if adverse effects or treatment-emergent worsening occur.

Fluoxetine for Bulimia Nervosa: dosing, monitoring binge-purge behaviors, and relapse prevention

Dosing and titration

Start fluoxetine for bulimia nervosa at 20 mg once daily for 7–14 days to assess tolerability, then increase to 60 mg once daily, which is the target dose used in clinical trials for reducing binge–purge frequency.

• Typical schedule: 20 mg daily ×1–2 weeks → 60 mg daily thereafter.
• Maintain 60 mg for a minimum of 8–12 weeks to judge response unless adverse effects force earlier change.
• If adverse effects limit tolerability, consider a slower titration (e.g., 20 mg increments every 1–2 weeks) or temporary dose reduction with subsequent rechallenge.
• Adolescents and those with low body weight or hepatic impairment: consult a specialist and use lower starting doses and closer follow-up.

Monitoring binge–purge behaviors and safety

Track binge and purge frequency with daily logs and structured assessments; quantify baseline episodes, then compare at 2, 4, 8, and 12 weeks.

• Behavioral targets: aim for ≥50% reduction in binge/purge episodes by 4 weeks and continued decline through 12 weeks; lack of meaningful reduction by 12 weeks warrants reassessment.
• Use validated tools when available (for example, the Eating Disorder Examination questionnaire or weekly episode counts) to document change and guide decisions.
• Monitor vitals and weight at baseline, weekly for the first month, then monthly for 3 months, then every 3 months while stable.
• Check serum electrolytes (sodium, potassium, bicarbonate) at baseline and whenever purging is active or dehydration suspected; repeat at intervals guided by clinical status.
• Order ECG if patient has cardiac disease, uses QT‑prolonging agents, or has severe electrolyte disturbances.
• Assess for new or increased suicidal ideation at each visit, especially in adolescents and young adults.
• Screen for SSRI adverse effects: insomnia, activation/agitation, gastrointestinal symptoms, sexual dysfunction, and hyponatremia (older adults at higher risk).

Document adherence at each contact and address barriers (side effects, schedule conflicts, cost). If adherence is confirmed but response is inadequate by 12 weeks on 60 mg, discuss adding evidence-based psychotherapy or specialist referral rather than automatic dose escalation.

• Combine with structured psychological treatment (cognitive-behavioral therapy designed for bulimia) for greater symptom control and skill-building.
• Consider consultation with an eating-disorders team if medical instability, severe comorbidity, or poor response.

Plan for relapse prevention using measurable triggers and a medication strategy.

• Continue fluoxetine at the effective dose for at least 6 months after remission of binge–purge behavior; extend treatment for recurrent illness or persistent risk factors.
• Define relapse markers (for example, return to baseline episode frequency for two consecutive weeks or a sustained 25–30% increase from nadir) and set a rapid-response plan: contact clinician, increase therapy contacts, and reassess electrolytes and safety.
• Offer periodic booster psychotherapy sessions (monthly to quarterly) for 6–12 months and reinforce meal regularity, coping skills, and trigger management.
• When stopping fluoxetine, plan a gradual discontinuation over several weeks when feasible; because fluoxetine has a long half-life, abrupt cessation carries less risk than shorter‑half‑life SSRIs but monitor for symptom return or discontinuation effects.

Fluoxetine for Premenstrual Dysphoric Disorder: dosing schedules and tracking symptom improvement

Start fluoxetine 20 mg daily; choose continuous daily dosing or luteal-phase dosing (20 mg daily beginning 14 days before expected menses and stopping on the first day of bleeding) based on cycle regularity and patient preference.

Continuous schedule: begin 20 mg once daily, reassess after 2–4 weeks for early symptom change and after 8–12 weeks for full effect. For partial response, increase to 40 mg daily; some clinicians use up to 60 mg/day under close follow-up. If side effects emerge, lower dose or switch strategy rather than rapid discontinuation.

Luteal-phase schedule: instruct the patient to start 20 mg daily either 14 days before expected menses or the day after a positive ovulation test, and stop on the first day of menstrual bleeding. Use luteal dosing when cycles are regular and symptoms are tightly linked to the premenstrual interval. If cycles are irregular, prefer continuous dosing for predictable coverage.

Symptom-onset (intermittent) dosing: for patients who prefer the briefest exposure, allow starting at the first clear premenstrual symptoms and continuing through menses; expect less consistent results than scheduled luteal dosing and monitor closely during the first three cycles.

Tracking protocol: record daily symptom ratings for at least two baseline cycles before initiating treatment using a validated tool such as the Daily Record of Severity of Problems (DRSP). Continue daily ratings throughout treatment. Log dose, cycle day, sleep, appetite, and adverse effects in the same diary to link changes to dosing and cycle phase.

Response criteria and timing: consider a clinical response as a ≥50% reduction in premenstrual symptom scores compared with baseline. Some patients report improvement in mood and irritability within days of starting luteal or continuous dosing; expect clearer, sustained improvement across 1–3 menstrual cycles. If no meaningful change after three cycles on a given schedule, switch strategy (luteal ↔ continuous), optimize dose, or consider alternate treatments.

Monitoring and practical notes: review adherence and accurate cycle timing before judging lack of efficacy. Check for common side effects (insomnia, nausea, sexual symptoms) at 2–4 weeks. Fluoxetine’s long half-life reduces abrupt withdrawal risks, but taper slowly after extended continuous use. Use ovulation predictor kits for precise luteal timing when cycle length varies by less than five days.

Communicate measurable goals with the patient (target percent reduction, specific symptoms to reduce such as anger or sleep disruption), use the daily diary to guide adjustments, and schedule formal reassessment after three treated cycles unless early escalation is needed for severe symptoms.

Starting Fluoxetine in Adolescents and Adults: managing common adverse effects and when to seek medical review

Begin with the lowest effective dose and arrange an early safety check: adolescents commonly start at 10 mg daily for 7 days then increase to 20 mg, while most adults start at 20 mg once daily; schedule a clinical review or phone check within 7–14 days to assess mood changes, activation, sleep, and suicidal thoughts.

Expect early-onset effects within days: nausea, headache, sweating, and sleep disturbance. Expect activation (restlessness, increased anxiety, akathisia) most often in the first 1–3 weeks; sexual dysfunction and weight change usually emerge after several weeks. Track symptom onset and severity using symptom checklists or a brief diary during the first month.

To reduce nausea, take the tablet with food and a full glass of water; if nausea persists beyond 7–10 days, consider dosing at bedtime or temporary dose reduction after clinician review. For insomnia, move the dose to morning; for daytime drowsiness, try evening dosing. If mild activation occurs, evaluate caffeine intake, sleep hygiene and anxiety symptoms before adjusting dose.

Handle marked agitation or akathisia proactively: arrange same‑day clinical review. Options include stopping dose escalation, reducing dose, or adding a short course of a benzodiazepine or propranolol under supervision. Do not ignore new or worsening restlessness–this can increase risk of suicidal behaviour in younger patients.

Address sexual side effects by asking direct, nonjudgmental questions at follow-up. If sexual dysfunction affects adherence, discuss switching to an alternative antidepressant (for example, bupropion in adults where appropriate) or adding treatments targeted to specific symptoms (e.g., phosphodiesterase inhibitors for erectile dysfunction) only after specialist advice.

Watch for interaction-related problems: avoid combining fluoxetine with MAOIs, linezolid, or other strong serotonergic agents without the recommended washout period (fluoxetine requires longer washout than most SSRIs). Check concomitant medications that increase bleeding risk (anticoagulants, antiplatelets, NSAIDs) and monitor for new bruising or prolonged bleeding.

Recognize emergency warning signs requiring immediate medical review or emergency care: sudden onset or worsening suicidal ideation or behaviour; severe agitation, uncontrollable anxiety, or akathisia; signs of serotonin syndrome (high fever, muscle rigidity, rapid heart rate, confusion, myoclonus, hyperreflexia); anaphylaxis (swelling of face or throat, breathing difficulty); seizures; chest pain; fainting or persistent severe hyponatraemia symptoms (confusion, weakness, vomiting).

Advise practical safety measures: keep a simple crisis plan and emergency contacts visible at home, avoid driving or operating heavy machinery until you know how the drug affects you, limit alcohol while adjusting dose, and ensure a responsible adult checks mood and behaviour closely during the first month for adolescents and young adults.

Follow-up framework: contact or face-to-face review at 1–2 weeks, clinical assessment at 4 weeks to judge early response and tolerability, and a fuller response review at 6–8 weeks. For adolescents, maintain weekly contact (phone or in-person) for the first month and regular parental/carer involvement with consent. Document side effects, adherence, sleep, appetite, suicidality, and any drug interactions at each visit.

If adverse effects persist despite simple measures (timing with food, dose timing changes, short-term supportive meds), arrange medication review to consider dose adjustment, switching agent, or specialist referral. Any uncertainty about risk or rare reactions should prompt immediate consultation with the prescriber or emergency services.