Using Diphenhydramine Hcl for Pets - A Benadryl Generic

How This Antihistamine Helps Your Pet With Allergies, Stings, Nausea, and More

By Sam Bourne.

  • Grass Allergy
  • Pollen Allergy
  • General Allergies

indications for Diphenhydramine HcL

Diphenhydramine HcL is an ethanolamine derivative H1 receptor antihistamine, with secondary sedative, anticholinergic, antitussive, and antiemetic effects. In other words, this drug blocks the part of the brain that responds to allergens (histamine), relaxes them, keeps them from coughing, and prevents nausea. Most offten used in pets that suffer from seasonal allergies, this medication is helpful when dealing with rashes, like pruritus or insect bites, or when dealing with motion sickness. Available in multiple strengths (prescription and OTC) and as a tablet or an injectable, there are a number of different ways to optimize the way your pet receives their treatment depending on their condition.


Diphenhydramine HcL should be used with caution in pets suffering from angle closure glaucoma, prostatic hypertrophy, bladder neck or pyloroduodenal obstruction, COPD, hyperthyroidism, cardiovascular disease, or hypertension. Should only be used in pregnant patients when the benefits outweigh the risks.

Taking diphenhydramine with CNS depressants might cause excessive depression of the central nervous system. MAOI inhibitors might intensify the anticholinergic effects of diphenhydramine. Diphenhydramine might overly enhance the effects of epinephrine, and counteract the anticoagulant effects of heparin or warfarin.


For dogs, anywhere between 1 - 4 mg/kg orally or IM every 8 hours
For cats, anywhere between 0.5 - 4 mg/kg orally or IM every 8 hours

Brand/Generic equivalents

Benadryl, Vetadryl

Side Effects

Possible side effects of diphenhydramine HcL are CNS depression, dry mouth, urine retention, vomiting, diarrhea, and loss of appetite. The sedative effects of diphenhydramine might lessen over repeated uses. In some cats, a paradoxical CNS excitation might occur.

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Diphenhydramine HcL at a glance

  • 1For dogs and cats
  • 2An antihistamine
  • 3Taken orally or IM
  • 4Treats allergies, motion sickness, and more

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