The Effects of Benadryl on Dogs

Benadryl is an antihistamine that blocks the body's autoimmune response to allergens like bug bites, pollen and mold. Although not FDA approved for veterinary use, it is commonly prescribed to alleviate canine discomfort from bug bites, motion sickness and vaccinations. Dogs generally receive 0.5 to 2 milligrams of plain Benadryl in pill form for every one pound of weight no more than every eight hours. As with any medication, it's best to ask your veterinarian first.

  1. Drowsiness

    • All antihistamines are sedatives, and Benadryl is no different. Your dog's behavior should be monitored closely when administering the medicine because an overdose can result in coma or death. Drowsiness and disorientation are common side effects of proper dosage, as are slowed responses and a dulled effect or interest in usual activities. Signs of overdose include excessive sleep and significantly slowed and weak breathing. In short, Benadryl might slow your dog down a bit, but it shouldn't put it entirely under.

    Appetite

    • Another Benadryl side effect can be loss of appetite. It's less common than drowsiness, which is almost certain to occur, but it's far more serious. Any major loss in appetite should be reported immediately to your veterinarian because it can signify an unusual allergy to antihistamines. In the likely event that your dog simply loses interest in food because of mental impairment, appetite loss may be diminished or avoided by feeding your dog before administering Benadryl.

    Gastrointestinal

    • Upset stomach can also result from giving Benadryl to dogs. Although rare, a dog's stomach can become so upset from Benadryl that it vomits or experiences diarrhea. These symptoms should be reported to your veterinarian immediately and are indications that your dog may be allergic to antihistamines. Upset stomach may be diminished or avoided by administering Benadryl with food.

    When Not to Use

    • Do not administer Benadryl to dogs with a known allergy to antihistamines. It also should not be used in combination with glaucoma, prostate disease, urinary obstruction or high blood pressure. If your pet is pregnant or nursing, Benadryl should be avoided. Always tell your veterinarian all of the medications your pet is taking, especially barbiturates or sedatives, as drug interactions can be dangerous.