ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
SSRI (Selective Serotonin Reuptake Inhibitor) Pregnancy: Avoid — associated with cardiac septal defects (first trimester) and persistent pulmonary hypertension of the newborn (third trimester). Switch to sertraline if antidepressant needed in pregnancy.

Paroxetine

Brand names: Seroxat

Adult dose

Dose: Depression: 20mg OD; increase by 10mg every 2–3 weeks if needed; maximum 50mg OD. OCD: 40mg OD (max 60mg). Panic disorder: 10mg OD initially, increase to 40mg OD (max 60mg). Social anxiety disorder: 20mg OD (max 50mg). PTSD: 20mg OD (max 50mg). GAD: 20mg OD (max 50mg).
Route: Oral
Frequency: Once daily (morning, with food)
Max: 60mg OD (OCD/panic); 50mg OD (depression, social anxiety, PTSD)
Paroxetine is the most potent inhibitor of CYP2D6 among SSRIs — significant drug interaction burden. Has notable anticholinergic and sedating properties. Worst discontinuation syndrome of all SSRIs — taper very slowly (over months if long-term use). Most serotonin-selective SSRI but also inhibits noradrenaline reuptake at higher doses.

Paediatric dose

Route: Oral
Frequency: Once daily
Max: Not applicable
Not licensed under 18 years in UK. MHRA black-box warning in paediatrics — increased suicidality and behavioural activation. Do not use in under-18s. Seek specialist child and adolescent psychiatry opinion.

Dose adjustments

Renal

eGFR <30: start at 10mg OD; max 20mg OD — reduced clearance.

Hepatic

Severe hepatic impairment: start at 10mg OD; maximum 20mg OD.

Clinical pearls

  • Tamoxifen interaction is clinically critical — paroxetine substantially reduces tamoxifen metabolism to active endoxifen; reduced anticancer efficacy. Switch to sertraline or venlafaxine (minimal CYP2D6 effect) in breast cancer patients on tamoxifen
  • Worst SSRI for discontinuation syndrome — never stop abruptly; taper over months for long-term users. Consider switching to fluoxetine (long half-life) before tapering if discontinuation is very difficult
  • Antidote: cyproheptadine 8mg oral for mild serotonin syndrome
  • Anticholinergic burden: avoid in elderly, BPH, narrow-angle glaucoma

Contraindications

  • MAOIs (within 14 days)
  • Thioridazine, pimozide (QT/CYP2D6)
  • Hypersensitivity to paroxetine

Side effects

  • Nausea (common)
  • Weight gain (more than other SSRIs)
  • Sedation / fatigue
  • Sexual dysfunction (common — dose-dependent)
  • Dry mouth, constipation (anticholinergic effects)
  • Sweating
  • Hyponatraemia (SIADH)
  • Severe discontinuation syndrome (dizziness, 'brain zaps', paraesthesia, flu-like symptoms)
  • Increased suicidality (under-25s)

Interactions

  • CYP2D6 inhibitor — most potent among SSRIs: significantly increases levels of codeine (risk of reduced analgesic effect as conversion to morphine inhibited), TCAs, antipsychotics, tamoxifen (reduces efficacy — switch antidepressant in breast cancer patients on tamoxifen)
  • MAOIs — contraindicated (serotonin syndrome)
  • Warfarin — increased bleeding risk; monitor INR

Monitoring

  • Mood and suicidality (first 4 weeks)
  • Weight (long-term)
  • Sodium in elderly
  • Discontinuation symptoms on dose reduction

Reference: BNFc; BNF 90; NICE CG90 (Depression); MHRA SSRIs in Paediatrics Safety Update. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Drugs
Pathways