Dogs are susceptible to most of the health problems that affect humans, and allergies are no exception. Dog owners want to help their beloved pets, so they often wonder, "Can I give my dog antihistamines?"

Antihistamines relieve allergy symptoms by blocking histamine receptors in smooth muscle and blood vessels. Veterinarians frequently recommend antihistamines for dogs. Owners can give their dogs antihistamines at home because the medications have a wide margin of safety, and dogs usually tolerate them well.

What Kind of Antihistamines Are Safe?

Most pharmacies and grocery stores carry antihistamines in several formulations. Read the active ingredients on the label to make sure it is just an antihistamine medication instead of a combination of drugs. Avoid liquid for dogs because liquid formulas have high alcohol content. The 25-milligram tablets are a good choice because they contain an antihistamine without any other active ingredients.

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What are Antihistamines For?

Antihistamine tablets start to relieve allergy symptoms within 30 minutes. It helps dogs with itchy or irritated skin, insect and flea bites, bee stings, and vaccine reactions. It also relieves hay fever symptoms such as sneezing, coughing, or a runny nose. Sometimes antihistamines help dogs with asthma, insomnia, car sickness, nausea, and anxiety.

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How Much of an Antihistamine Does a Dog Need?

The general guidelines for antihistamine dosage are 10-mg for dogs that weigh 30-pounds or less, 25-mg for 30-50 pound dogs, and 50-mg for dogs over 50-pounds. Calculate an exact dose with the simple formula of 1-milligram of medication per pound of body weight. Give the dog an antihistamine two or three times a day with at least 8 hours between doses.

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Side Effects of Antihistamines

The most common side effects of antihistamines are drowsiness and disorientation. Less common side effects include dry mouth, diarrhea, vomiting, lack of appetite, constipation, dilated pupils, excessive drooling, panting, or agitation. Contact a veterinarian immediately if a dog experiences serious adverse effects such as urinary retention, rapid heartbeat, seizures, or difficulty breathing. Serious adverse effects are very rare. Most dogs do not experience any side effects except drowsiness.

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Antihistamines may not be safe for puppies. Contact a veterinarian before giving antihistamines to a puppy under 12 weeks old. Antihistamines should not be given to dogs with prostatic disease, glaucoma, hyperthyroidism, or cardiovascular disease. Take the dog to a veterinarian if allergy symptoms include facial swelling or difficulty breathing. Over-the-counter antihistamines are not meant to treat severe or life-threatening allergic reactions.

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Administering Antihistamines

Dogs do not always cooperate when medication is necessary, but there are several ways to make medication more palatable. Fold a piece of meat around an antihistamine tablet or push the tablet into a bite-sized soft treat, so the dog does not realize the tablet is there. Crushed tablets can be mixed into gravy on canned dog food. Capsules contain powder or granules. Open the capsule and mix the contents into wet or moist food.

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Medication Interactions

Antihistamines are safe medications to help dogs with anxiety or motion sickness, but they may not be safe if the dog is taking other medications for anxiety. Antihistamines can interact negatively with central nervous system depressants. They can also interfere with muscle relaxants, narcotics, anti-seizure medications, sedatives, and blood thinners.

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Topical Antihistamines

Antihistamines come in topical forms such as lotions, creams, and ointments. Some topical products are safe for dogs, but antihistamines should be the only listed active ingredient. Avoid topical products with numbing agents. Some ointments containing antihistamines have antibiotic ingredients too. The antibiotic ointments should be safe, but use a small amount of the product first in case the dog is allergic to any ingredients.

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When Not to Use Antihistamines

Antihistamines are not helpful for skin conditions that are not caused by allergies or inflammation. Dogs with ringworm lose their fur around the site of infection, and the skin may look red and inflamed, but ringworm is a fungus. Mites and fleas sometimes cause moist red sores on a dog's skin. Antihistamines may help relieve itching around the sores temporarily, but the sores will not heal until the mites and fleas are treated. A veterinarian should examine any skin condition that looks unfamiliar or does not heal within 2-3 days.

skin condition, fleas, mites, ringworm mikedabell / Getty Images


Treating Illness

Many antihistamines are over-the-counter drugs, but sometimes they are used to treat serious illness. Veterinarians give antihistamines for mast cell tumors. Mast cells tumors are made up of cells that normally fight inflammation and infection. Veterinarians use antihistamines to counteract the flood of histamines released by mast cell tumors. Antihistamines are used in conjunction with heartworm treatment. Heartworms die inside a dog's heart and lungs after treatment. Antihistamines help control symptoms as the dog's body reabsorbs the dead heartworms.

heartworm, mast tumor, symptoms, illness gilaxia / Getty Images


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