Diphenhydramine for Dogs and Cats Guide Antihistamine Medication That Offers Relief To Allergic Reactions, Nausea, and Vomiting

Gastritis (Vomiting) Asthma

Diphenhydramine 50mg

Allergy Relief
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Indications for Diphenhydramine Rx

Diphenhydramine belongs to the antihistamine, H1 antagonist class. The medication is chiefly indicated for the treatment of anaphylaxis, allergic reactions, urticaria, sedation, motion sickness, vertigo, nausea and vomiting. Diphenhydramine is effective to control muscle tremors caused by certain toxins and medications. The medication is contraindicated for hypersensitivity, acute asthma attack and lower respiratory tract disease. The active ingredient in the medication, diphenhydramine hydrochloride, works by blocking the influence of histamine at H1 receptor sites. This in turn results in the reduction of smooth muscle contraction.


It is not advised to mix or dissolve the slow release capsule in food. It is not recommended to use diphenhydramine available in combination products containing sinus or cold medicine. Do not use the medication in nursing or pregnant animals. It is advised not to use the medication in animals with prostate disease, urinary obstruction, glaucoma, and high blood pressure. Extreme caution is required when used with other central nervous system depressant drugs like tranquilizers or barbiturates and in pets with lower respiratory diseases like asthma. Make sure to inform the veterinarian or pharmacist about the medication the pet is taking. The medication should be stored at room temperature, away from excess heat, moisture and light.


The medication is available as a prescription strength capsule and injectable in addition to OTC tablet, capsule, elixir and shampoo. The standard dosage in dogs and cats is 0.5-2mg/lbs orally every 8-12 hours. The injectable diphenhydramine is found in the concentrations - 10 mg/ml and 50 mg/ml.

Side Effects

More commonly, side effects like lethargy, dry mouth, urinary retention, vomiting, diarrhea, and lack of appetite are observed. The sedative effects of the medication could increase over time. The use of oral diphenhydramine in cats is observed with profuse, yet brief, drooling.

Brand/Generic Equivalents

Benadryl, Histacalm

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