At a glance
Effects
- Allergic symptom relief: Blocks H1 receptors to reduce itching, sneezing, runny nose, and hives in allergic rhinitis, conjunctivitis, and chronic urticaria [1].
- Mast-cell stabilization: Prevents release of histamine and other inflammatory mediators from mast cells, offering ongoing protection beyond immediate symptom relief [1][3].
- Asthma prophylaxis (adjunct): Reduces frequency, severity, and duration of asthma attacks when used long-term alongside other antiasthma medications; not for acute attacks [6].
- Eosinophil suppression: Inhibits eosinophil infiltration and activation, dampening late-phase allergic responses including reactions to platelet-activating factor [4].
- Sedation (side-effect): Crosses the blood-brain barrier and causes drowsiness in ~10–20% of patients, especially early in treatment; typically diminishes within 1–2 weeks [7].
Non-competitive H1-antihistamine & mast cell stabilizer
~21–22 h (terminal elimination phase) [10]
Oral (tablet/syrup) or ophthalmic (eye drops) [2]
6–12 weeks (oral, anti-allergic max effect) [5]
~50% (oral; 50% first-pass hepatic metabolism) [11]
About Ketotifen
Every point here is drawn from public medical and harm-reduction sources. A bracketed number after a claim — like [1]— is a reference: tap it to open the exact source it's based on (numbered list at the bottom). It is not a rating or score. Educational information, not medical advice.
Product specifics
- Est. delivery
- 3–7 business days · EU tracked
Product details as stated by the vendor (claims, not independently verified). Delivery is our standard EU estimate.
What it is
How it works
Ketotifen works through a dual mechanism: it blocks H1 histamine receptors, preventing histamine from triggering itching, swelling, and inflammation, while simultaneously stabilizing mast cells to inhibit the release of inflammatory mediators in the first place [1][3]. It also inhibits infiltration and degranulation of eosinophils and attenuates responses to platelet-activating factor, giving it broader anti-allergic coverage than a simple antihistamine [4]. It crosses the blood-brain barrier more readily than newer antihistamines, which explains its sedative side effect [4]. Maximum anti-allergic effect from oral use requires at least 6–12 weeks of continuous administration [5].
Risks & side effects
Most important: The most clinically significant risk is reversible thrombocytopenia (dangerous drop in platelet count) when ketotifen is combined with oral antidiabetic agents such as metformin or glyburide; this combination should be avoided or platelet counts monitored closely [7][8].
Common
- Drowsiness / sedation — occurs in ~10–20% of patients, especially at higher doses; typically subsides within 1–2 weeks [7]
- Weight gain (reported average ~5 kg during long-term use) [5]
- Dry mouth [5]
- Dizziness, headache, nausea — reported in 1–2% of patients at treatment initiation [7]
- Fatigue, diarrhea [7]
Serious
- Reversible thrombocytopenia (low platelet count) when combined with oral antidiabetic agents [7][8]
- Enhanced CNS depression / respiratory depression when combined with sedatives, opioids, benzodiazepines, or alcohol [5]
- Abdominal pain, constipation, vomiting [5]
- Elevated liver enzymes (observed in chronic high-dose toxicity studies) [9]
Safety & harm reduction
- Known hypersensitivity to ketotifen or any formulation component [12]
- Concurrent oral antidiabetic agents (glyburide, metformin) unless platelet counts are closely monitored — risk of reversible thrombocytopenia [7][8]
- Acute asthma attacks or status asthmaticus — ketotifen has no bronchodilating effect and must not be used as a rescue therapy [6]
- Pregnancy and breastfeeding — not recommended; likely excreted in breast milk [13]
- Sedatives, hypnotics, opioids, benzodiazepines, alcohol — additive CNS and respiratory depression [5]
- Other antihistamines — additive sedative and anticholinergic effects [5]
- Oral antidiabetic agents (metformin, glyburide) — reversible thrombocytopenia; avoid or monitor platelet counts [7]
- Tricyclic antidepressants — potentiation of anticholinergic effects (dry mouth, urinary retention) [13]
- CYP3A4 / CYP2D6 substrates — oral ketotifen may alter metabolism of co-administered drugs via these pathways [14]
- Titrate oral dose slowly in the first week (start at half the target dose in the evening) to minimise initial sedation [11]
- Allow 6–12 weeks of continuous dosing before assessing maximum anti-allergic therapeutic benefit [5]
- Do not abruptly discontinue concurrent antiasthma medications (corticosteroids, bronchodilators) when starting ketotifen — taper under medical supervision [6]
- Remove soft contact lenses before instilling eye drops; wait ≥10 minutes before reinserting if solution contains benzalkonium chloride [12]
Dosage context
Commonly reported oral dose for adults and older children: 1 mg twice daily (with food); for young children (6 months–3 years) 0.5 mg twice daily [7]. To minimise early sedation, starting with half the target dose in the evening for the first 5 days before titrating to full dose is commonly recommended [11]. These are clinically observed ranges, not a prescription — individual medical guidance is required. Eye-drop formulation: 1 drop in affected eye(s) twice daily, 8–12 hours apart (OTC labelling) [12].
Sources
- 1.Medtigo — Ketotifen (systemic) pharmacology
- 2.Synapse/PatSnap — Ketotifen Fumarate mechanism & formulations
- 3.PMC — Ketotifen in chronic urticaria (PMC4309375)
- 4.ScienceDirect Topics — Ketotifen pharmacology overview
- 5.Wikipedia — Ketotifen
- 6.Mayo Clinic — Ketotifen oral route
- 7.ScienceDirect — Ketotifen in chronic urticaria (full article)
- 8.Harbor Compounding — Ketotifen Capsules prescriber guide
- 9.Canadian Product Monograph — Ketotifen Ophthalmic Solution
- 10.MedicinesFAQ — Ketotifen half-life & pharmacokinetics
- 11.Harbor Compounding — Ketotifen Capsules (bioavailability / titration)
- 12.RxList / Zaditen — Ketotifen ophthalmic monograph
- 13.Biomedicus — Ketotifen Fumarate side effects & interactions
- 14.Synapse/PatSnap — Ketotifen CYP interactions
- 15.PMC — Efficacy/safety ketotifen eye drops (PMC1920791)
This information is provided for educational and harm-reduction purposes only. It is not medical advice. These substances can carry serious health risks; effects and safe use vary by individual. Consult a qualified healthcare professional before use. Legal status varies by country — it is your responsibility to know your local law. We do not encourage misuse.