• The following is a list of options for antihistamines that are known to be effective in cats. The name of the active ingredient is listed, with the name of a well known brand in parentheses. Also listed are approximate doses and any precautions.

    CAUTION: Do not purchase antihistamines that are combination products (multi-symptom, cold/flu medicines, decongestants, etc.), especially products that contain decongestants (often labeled with a D, as in “Zyrtec-D”). These products often contain a high level of stimulants that are toxic, even life-threatening, to animals. In addition, products containing acetaminophen (active ingredient in Tylenol) are deadly for cats.


    1) Clemastine (“Tavist”) – Probably one of the most effective antihistamines in cats.

    Available in: 1.34mg tablets and 0.67mg/5ml liquid


    CATS: ¼ to ½ tablet once daily (1.34mg tablets).

    Precautions: Safe in pregnancy, but crosses into milk during lactation.

    May cause: sedation, hyperactivity, dry mouth, or diarrhea.

    Do not use if: Urinary or GI obstruction, or severe heart disease

    NOTE: Do not confuse this product with a similar product called “Tavist N.D,”

    which is a different type of antihistamine, and is not recommended.

    2) Chlorpheniramine (“Chlor Trimeton”)

    Available in: 2mg ,4mg ,and 8mg tablets, and 2mg/5ml liquid


    CATS: 1-4 mg per cat once or twice daily. Very effective in cats.

    Precautions: Safe in pregnancy.

    May cause: sedation, hyperactivity, or dry mouth,

    Do not use if: high blood pressure, GI or urinary obstruction, hyperthyroidism, heart disease.

    NOTE: Do not use products that contain any other active ingredients (like acetaminophen). These other products are potentially toxic to your pet (acetaminophen is deadly in cats!).

    3) Cetirazine (Zyrtec)

    This may be the best antihistamine for eosinophils (one of the primary cell types associated with allergies). It is a formerly prescription only medication that is now available over the counter.

    Available in: 5mg and 10mg tablets


    CATS: 5mg ½ to 1 tablet 1 or 2 times daily.

    NOTE: Twice daily dosing is often needed.


    1) Hydroxyzine (Atarax)

    We can provide a written prescription for you, if you want to try this antihistamine.

    Available in: 10mg, 25mg, and 50mg tablets


    CATS: ½ to 1 10mg tablet 2-3 times daily.

    Precautions: NOT safe in pregnancy.

    May cause: Sedation most likely. Cats may get increased thirst, depression or behavioral changes.

    Do not use if: Urinary or GI obstruction, or severe heart disease.

    NOTE: Also has anti-nausea effect, and can be used for motion sickness.

    2) Cyproheptadine (Periactin)

    This is one of the more effective antihistamines for cats. We carry this medication in stock at our hospital.

    Available in: 2mg and 4mg tablets (we only keep 4mg tablets in stock)


    CATS: 4 mg tablet ¼ to 1 tablet 2 times daily.

    Precautions: Testing has shown no effects on pregnancy, but absolute safety in pregnancy has not been proven. Use cautiously.

    May cause: sedation, dry mouth, hyperexcitability

    Do not use if: Urinary or GI obstruction, or heart disease.

    NOTE: Also has an appetite-stimulating effect in cats. Be cautious of excessive weight gain.