Prozac. What diseases does it treat?

Recommendation: Start fluoxetine (Prozac) at 20 mg once daily for adults with major depressive disorder and reassess clinical response after 2–4 weeks; if symptoms persist, increase to 40 mg, with specialist-managed escalation up to 80 mg/day for resistant cases.

Prescribing guidance by condition: for major depressive disorder typical dosing is 20–40 mg/day; obsessive–compulsive disorder commonly requires 20–60 mg/day; panic disorder can begin at 10 mg for one week then increase to 20 mg/day, titrating up to 60 mg/day if needed; bulimia nervosa is FDA-approved at 60 mg/day; premenstrual dysphoric disorder responds to 20 mg daily or 20 mg during the luteal phase. For adolescents and older adults start lower (e.g., 10–20 mg/day) and adjust based on tolerability.

Pharmacokinetics and interactions: fluoxetine has a long elimination profile–parent drug half-life around a few days and the active metabolite norfluoxetine persists for 4–16 days–which reduces abrupt withdrawal but prolongs drug interactions. Allow at least 5 weeks after stopping fluoxetine before initiating a monoamine oxidase inhibitor (MAOI); wait at least 14 days after stopping an MAOI before starting fluoxetine. Fluoxetine strongly inhibits CYP2D6; review co-medications (including tricyclics, some antipsychotics, beta-blockers and tamoxifen) and adjust or substitute as needed.

Safety and monitoring: watch for new or worsening suicidal thoughts in people under 25, especially during the first weeks and after dose changes. Common adverse effects include insomnia, nausea, headache and sexual dysfunction; report significant bleeding when combined with anticoagulants or NSAIDs. Use caution in pregnancy–discuss maternal benefit versus neonatal risks such as poor neonatal adaptation and a possible small increase in persistent pulmonary hypertension of the newborn–and consider obstetric consultation. Reduce dose in severe hepatic impairment and avoid concurrent use with pimozide or MAOIs. Plan follow-up at 2–4 weeks to assess response, side effects and need for dose adjustment.

Dosing and titration for adult major depressive disorder

Begin fluoxetine 20 mg once daily in the morning for most adults with major depressive disorder; reduce to 10 mg daily for frail, elderly, or highly sensitive patients and increase only after assessing tolerability.

Initial dosing and upward adjustment

Maintain 20 mg/day for at least 2–4 weeks to evaluate tolerability. If minimal improvement after 4 weeks, increase to 40 mg/day. Make dose changes in 10–20 mg increments and allow at least 1–2 weeks between adjustments to monitor side effects, keeping in mind fluoxetine’s long half-life delays steady state. Target doses commonly fall between 20–40 mg/day; reserve doses up to 80 mg/day for severe, treatment-resistant cases and use such higher dosing under close clinical supervision.

Give fluoxetine in the morning to reduce insomnia risk. Once-weekly 90 mg capsules may replace daily dosing for patients stabilized on 20–40 mg daily; initiate the 90 mg weekly dose seven days after the last daily dose to maintain steady exposure and support adherence.

Monitoring, discontinuation and special populations

Assess tolerability at 1–2 weeks and clinical response at 4–6 weeks. Monitor for increased agitation, anxiety, sleep disruption, gastrointestinal effects, and any emergence of suicidal ideation–pay particular attention to patients under 25 during the first month of treatment. When combining with other serotonergic drugs, watch for signs of serotonin syndrome.

Stop fluoxetine gradually after prolonged use to minimize discontinuation symptoms, although its long half-life reduces withdrawal risk compared with shorter-acting SSRIs. Allow a five-week washout before starting a monoamine oxidase inhibitor (MAOI) after fluoxetine; wait 14 days after stopping an MAOI before initiating fluoxetine.

Reduce the starting dose and slow titration in patients with significant hepatic impairment. Renal impairment generally does not require routine dose adjustment, but monitor clinical response. For pregnancy or breastfeeding, individualize dosing in consultation with current obstetric and lactation guidance.

Managing common side effects during the first month of Prozac therapy

If you experience mild nausea, take your dose with a light meal and sip ginger tea or chew ginger candies; split large meals into smaller portions throughout the day and keep hydrated with 500–1,000 ml extra fluids daily if tolerated.

Timing and sleep: take the dose in the morning if you feel energized or restless after dosing; take it in the evening only if you feel drowsy. Reduce late-afternoon caffeine, maintain a consistent bedtime routine, and limit screen use for 60 minutes before sleep to reduce insomnia risk.

Nervousness, jitteriness, or initial anxiety (occurs in roughly 5–15% of patients): use short sessions of paced breathing (4–6 breaths/min for 3–5 minutes), brisk 10–20 minute walks, and schedule a follow-up within 1–2 weeks to consider a temporary dose adjustment or a short-term anxiolytic if symptoms impair daily function.

Headache and dizziness (approx. 10–30%): check hydration and salt intake, avoid sudden standing, and take simple analgesics such as acetaminophen or ibuprofen per label instructions. If headaches exceed 48–72 hours or intensify, contact your clinician.

Gastrointestinal upset and diarrhea: use loperamide for brief, symptomatic relief only after checking with your prescriber; maintain bland foods (BRAT approach) and electrolyte solutions for persistent loose stools.

Sexual side effects (variable; reported in many SSRI trials): track onset and severity with a brief log; discuss alternatives or adjunctive strategies with your prescriber if problems continue beyond four weeks or affect relationships.

Appetite and weight changes: weigh yourself weekly during the first month; follow a structured meal plan and add two 10–20 minute moderate-intensity activity sessions per week to help stabilize appetite changes.

When side effects typically change: many mild adverse effects start within 3–7 days and decrease by weeks 2–4. Persistent or worsening symptoms after four weeks merit clinical review.

Red flags – contact your clinician immediately

new or worsening suicidal thoughts, sudden severe agitation or confusion, fever with muscle stiffness, fast heartbeat or fainting, severe allergic reaction (rash, swelling, trouble breathing), signs of serotonin syndrome (high fever, rigid muscles, rapid changes in consciousness), persistent vomiting/diarrhea with dehydration, or unexplained bruising/bleeding.

Practical tracking and communication

keep a daily symptom diary (time of dose, sleep hours, hunger, side-effect score 0–10); bring it to the 2–4 week follow-up. If side effects limit work, relationships, or self-care for more than two weeks, contact your prescriber before making any dose changes or stopping medication.

Prozac for obsessive-compulsive disorder: expected timelines and response markers

Initiate fluoxetine at 20 mg once daily for most adults with OCD; expect measurable symptom reduction by 4–6 weeks, clearer improvement by 8–12 weeks, and potential full response by roughly 3 months or longer.

Measure response objectively with the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) and clinician global impressions. Use these thresholds: a 25–35% drop in Y-BOCS generally denotes clinical response; ≥35%–50% indicates marked response; remission often corresponds to Y-BOCS ≤7–10. On the Clinical Global Impression–Improvement (CGI-I) scale, scores of 1–2 (very much or much improved) align with meaningful benefit.

Watch for early signal: a ≥15–20% Y-BOCS decrease by weeks 2–4 predicts higher likelihood of later response. If you see steady month-to-month improvement, continue the current regimen. If there is minimal change (<15–20%) by week 4, maintain treatment but reassess dose, adherence, comorbidities, and concurrent psychotherapy; avoid premature switching before completing an adequate trial.

Define an adequate trial as approximately 8–12 weeks at a therapeutic dose for OCD (many patients require 40–60 mg/day). If Y-BOCS reduction remains <25% after 12 weeks on a dose of at least 40 mg/day, consider one or more of the following: add exposure and response prevention (ERP) therapy if not already in place; consult psychiatry about antipsychotic augmentation (low-dose risperidone 0.5–2 mg/day or aripiprazole 2.5–10 mg/day are common options); evaluate switching to clomipramine or another SNRI/SSRI in specialist hands, with attention to interactions and side effects.

Use functional markers as well as scale scores: decreased time spent on obsessions/compulsions, improved occupational or social functioning, and reduced avoidance signal clinical benefit. Continue the medication that produced response for at least 12 months to lower relapse risk; if stopping, taper slowly under clinical supervision and monitor for symptom return. Refer to a psychiatrist promptly for treatment-resistant or severe cases, poor insight, suicidal ideation, or complex comorbidity.

Treating panic disorder and social anxiety with Prozac: dose adjustments and relapse prevention

Begin adults with fluoxetine 10 mg once daily for 7 days, then increase to 20 mg; target 20–40 mg/day for panic disorder and 20–60 mg/day for social anxiety, adjusting by 10–20 mg increments based on clinical response and tolerability.

Dose adjustment protocol

If symptoms persist with little change after 4 weeks at 20 mg, raise the dose by 10–20 mg and reassess after another 4–8 weeks. For clear partial response at 6–8 weeks, consider a further 10–20 mg increase. Expect meaningful symptom reduction by 8–12 weeks; if no response by 12 weeks at an adequate dose, reassess diagnosis, comorbidity, adherence and consider alternative treatments. Observe a maximum daily dose of 80 mg, while recognizing most patients with these anxiety disorders respond within 20–60 mg.

Use lower initial doses and slower upward titration for older adults, patients with hepatic impairment, or those taking strong CYP2D6 inhibitors. For severe, early-onset panic with high-frequency attacks, consider temporary adjunctive short-acting benzodiazepine for 2–4 weeks to control acute symptoms while fluoxetine takes effect; avoid long-term benzodiazepine reliance and reassess regularly.

Relapse prevention and discontinuation strategy

Maintain the effective dose for at least 12 months after remission for a first episode of panic disorder or social anxiety. For recurrent episodes, chronic symptoms, or incomplete psychosocial recovery, extend maintenance to 24 months or longer based on clinical judgment. Combine fluoxetine with cognitive-behavioral therapy to reduce relapse risk and improve coping skills.

When planning discontinuation, taper gradually. For treatment duration under 6 months, lower the dose by approximately 10–25% every 1–2 weeks. For treatment longer than 6 months, decrease by about 10–20% every 2–4 weeks; pause or slow the taper if withdrawal-like symptoms (increased anxiety, dizziness, irritability, insomnia) appear. If relapse occurs after stopping, reinstate the previous effective dose and continue maintenance as clinically indicated.

Condition	Starting dose	Typical target range	Titration steps	Maintenance length	Taper suggestion
Panic disorder (adult)	10 mg ×7 days → 20 mg	20–40 mg/day (up to 60 mg if needed)	Increase 10–20 mg every 2–4 weeks if inadequate response	At least 12 months after remission; 24+ months for recurrent cases	Reduce 10–25% every 1–2 weeks (<6 months); 10–20% every 2–4 weeks (>6 months)
Social anxiety disorder (adult)	10 mg ×7–14 days → 20 mg	20–60 mg/day (individualize by severity)	Increase 10–20 mg every 2–4 weeks; reassess at 8–12 weeks	At least 12 months after remission; consider longer for chronic course	Same taper principles; slower taper for long-term users

Switching antidepressants: practical tapering and cross-titration with Prozac

If you plan a switch to Prozac (fluoxetine), choose the strategy by the prior agent's half-life and discontinuation risk: short‑half‑life SSRIs/SNRIs can be cross‑tapered; drugs with high discontinuation risk or MAOIs require staged washouts.

• Key pharmacology to guide timing:

  • Fluoxetine parent half‑life ≈ 1–4 days; active metabolite norfluoxetine ≈ 7–15 days; full washout may take several weeks.
  • Interaction risk: fluoxetine is a strong CYP2D6 inhibitor (also inhibits CYP2C19) – anticipate higher levels of tricyclics, some antipsychotics, beta‑blockers and certain opioids.
  • Serotonergic overlap: overlapping two serotonergic agents raises serotonin syndrome risk – if overlap is necessary, use lowest practical dose and close monitoring.

• MAOI rules (nonnegotiable):

  • Starting fluoxetine after stopping an MAOI: wait 14 days.
  • Starting an MAOI after stopping fluoxetine: wait 5 weeks.

• Practical cross‑taper templates (examples only; adjust for clinical context):

  1. From sertraline, escitalopram, citalopram (moderate discontinuation risk) – cross‑taper over ~2 weeks:

     • Reduce original SSRI by ~25–50% during week 1; start fluoxetine 10 mg on day 1.
     • Week 2: reduce original SSRI to low dose or stop; increase fluoxetine to 20 mg if tolerated.
     • Monitor for agitation, autonomic signs, new headache, myoclonus.

  2. From paroxetine or venlafaxine (high discontinuation risk) – conservative plan, 3–6 weeks:

     • Taper paroxetine by 10 mg every 1–2 weeks; taper venlafaxine by 25–50% every 1–2 weeks until at low dose.
     • When dose is minimal, stop the prior drug and wait 2–7 days for venlafaxine (longer if severe symptoms) or 5–7 days for paroxetine before initiating fluoxetine 10 mg.
     • Increase fluoxetine to 20 mg after 7–14 days if tolerated; extend taper pace if withdrawal symptoms appear.

  3. From bupropion or mirtazapine – lower serotonin overlap risk:

     • Either cross‑taper over 1–2 weeks or stop the prior drug and start fluoxetine 10 mg next day; avoid high bupropion doses with seizure history.

  4. From tricyclic antidepressants (TCAs) – watch CYP2D6 interactions:

     • Taper TCA by ~25% every 1–2 weeks to limit anticholinergic withdrawal and orthostatic effects.
     • If starting fluoxetine while residual TCA remains, reduce TCA dose by ~30–50% and obtain plasma levels where available; monitor for anticholinergic toxicity and QTc prolongation.

• Monitoring checklist during the switch:

  • Assess for serotonin syndrome daily in first 2 weeks of overlap (restlessness, hyperreflexia, clonus, hyperthermia).
  • Check serum sodium at baseline and within 1–2 weeks for elderly or concurrent diuretic use (hyponatremia risk).
  • Review medication list for CYP2D6 substrates (reduce doses or obtain levels for TCAs, some antipsychotics, atomoxetine).
  • Instruct patient to report new severe agitation, fever, stiff muscles, or altered mental status immediately.

• Practical dosing notes:

  • Start fluoxetine at 10 mg/day for sensitive patients (elderly, anxious, polypharmacy); typical target 20 mg/day for adults with major depression.
  • When switching from a drug with short half‑life, do not escalate fluoxetine rapidly during overlap; wait 7–14 days to assess tolerability.
  • If reducing a CYP2D6‑metabolized TCA or certain antipsychotics, anticipate needing lower maintenance doses after fluoxetine initiation and check ECG if QT‑prolonging agents are present.

• Special populations:

  • Pregnancy/breastfeeding: discuss maternal relapse risk versus fetal/neonatal exposure; coordinate with obstetrics and lactation specialists before switching.
  • Elderly: use lower starting doses (10 mg) and slower taper of prior drug; monitor sodium and fall risk.
  • History of seizures: avoid high‑dose bupropion concurrently; use slow cross‑taper and consult neurology if unclear.

Document the chosen plan, expected timeline, and specific warning signs; recheck within 1 week of dose change and at 4 weeks, then monthly until stable.