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Dogs can develop allergic reactions to food, medications, insect bites, and environmental allergens such as pollen and dust mites. If your dog is scratching more than usual, you might be tempted to reach for something in your medicine cabinet to try to ease their discomfort. Benadryl, or diphenhydramine for dogs, is an over-the-counter human medication that veterinarians commonly use to treat allergies, travel anxiety, and motion sickness.
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Depending on your dog’s age, health, and the type of allergen, Benadryl may not be the best choice for treating your dog. Some human medications are safe for dogs, so long as they’re used appropriately and under a veterinarian’s guidance. However, humans and dogs react differently to medications, which is why veterinarians caution against making independent decisions about medicating your pet.
Before giving your dog any human medication, consult with your veterinarian and read the ingredients list to check for xylitol. Your vet can advise how much Benadryl to give your dog or suggest other treatment options for managing allergies or anxiety. Here is what to know about the uses, side effects, and dosages of diphenhydramine or Benadryl for dogs.
What Is Benadryl, and How Does it Work?
“Benadryl is an antihistamine, used to treat histamine-type allergic reactions and other conditions, ‘off-label’ or ‘extra label’ in humans, dogs, cats, ferrets, small mammals, birds, horses, and cattle when directed by a veterinarian,” says Dr. Jerry Klein, DVM, Chief Veterinarian for the American Kennel Club. Off-label refers to using a drug for health conditions that haven’t been approved by the U.S. Food and Drug Administration (FDA). It can also mean using a different dosage or form than what was originally approved, such as when children are given a smaller dose of a medication approved for adults.
Benadryl is the brand name for the active ingredient diphenhydramine HCl. Diphenhydramine is a first-generation antihistamine, classified as an ethanolamine derivative, which means that it can cross the blood-brain barrier. This aspect of the drug makes it very effective but also increases the risk of adverse side effects. Although Benadryl isn’t FDA-approved for veterinary use, it’s considered safe for dogs and is commonly used in veterinary practices across the U.S.
Diphenhydramine works by blocking the receptors that receive histamines in the body. As a result, this medication relieves many of the symptoms associated with allergies, such as itching, sneezing, and hives. The body still produces histamines, but the receptor antagonist blocks the receptors from registering histamines.
As with any medication, always observe your dog closely after administration to ensure they don’t have any adverse reactions. If you have additional questions about diphenhydramine or Benadryl for dogs, contact your veterinarian for more information. Like with any medicine, human or canine, also remember to keep it out of your dog’s reach.
When Should You Use Benadryl for Dogs?
Benadryl has several important uses and effects in dogs, Dr. Klein says. For example, it’s used to treat acute inflammatory and allergic conditions in dogs, such as bee stings, insect bites, seasonal allergies, and allergic reactions. However, as he noted, Benadryl isn’t used to treat food sensitivities or food allergies.
If your dog has an allergic or inflammatory condition, you may notice one or more of the following allergy symptoms:
“Benadryl has commonly been used to treat itchy skin caused by seasonal allergies, though recent findings have not found it to be as helpful as once thought, except in the case of hives (urticaria),” he says. In a 2020 study of Beagles, with a randomized, double-blinded crossover design, researchers found that oral diphenhydramine failed to show an inhibitory effect. Another drug, oral cetirizine, was effective at reducing histamine and preventing allergic reactions. Neither drug had any adverse effect on dogs during the study.
“Since Benadryl can cause drowsiness, it may reduce the amount of scratching due to its sedative effects,” he says. Accordingly, Benadryl can be used as a mild tranquilizer to help calm anxious dogs or relieve symptoms of mild-to-moderate travel anxiety in pets. Still, it’s best to talk to your veterinarian or an animal behaviorist to determine and treat what’s causing the anxiety.
Aside from its sedative properties, “diphenhydramine has a strong anti-nausea effect that makes it helpful in treating dogs suffering from motion sickness,” he says. “Though it is not helpful in cats for this condition.”
In some cases, veterinarians prescribe diphenhydramine during heartworm treatment to help reduce the risk of an allergic reaction to heartworm treatment therapy. Another use of Benadryl is treating dogs with mast cell tumors, which release histamine, he says. Benadryl helps mitigate the effects of this massive histamine release caused by mast cell degranulation.
When Should You Avoid Using Benadryl?
“It is always recommended to consult with a veterinarian before using diphenhydramine or Benadryl on your dog or pet,” Dr. Klein says. “Benadryl should not be used in pediatric or neonatal pets or pets that are allergic to this drug or similar antihistamines.” You should also consider your dog’s age and allergy history, as young puppies can be quite sensitive to medications.
You should be cautious about using Benadryl if your dog is pregnant, lactating, geriatric, a working dog, or has any of the following conditions:
- Glaucoma
- Enlarged prostate
- Intestinal or urinary obstruction
- Elevated thyroid levels
- Heart disease
- Hypertension
- Chronic obstructive pulmonary disease (COPD)
- Seizure disorders
In addition, make sure to give your veterinarian a complete list of all the medications and supplements your dog is taking, since these can interact with Benadryl. One example is using Benadryl in combination with anticholinergic drugs, tricyclic antidepressants, and other sedatives or pain medications, he says. Anticholinergic drugs block a neurotransmitter called acetylcholine, which is key to the functioning of the parasympathetic nervous system. Unwanted effects of anticholinergic drugs include blurred vision, confusion, and loss of balance.
Another caution about using Benadryl concerns the possibility of a delayed diagnosis and subsequent treatment. For instance, allergy symptoms like redness and itchiness may be signs of a more serious condition, in which case giving your dog Benadryl wouldn’t address the underlying issue. Red, goopy eyes could be a symptom of allergies. It could also be a sign of glaucoma or dry eye, which require timely treatment to avoid scarring and vision loss.
What Are the Side Effects of Benadryl?
Most side effects occur within the first hour of exposure, so monitor your dog carefully during this time. Common side effects associated with using Benadryl for dogs include:
- Lethargy
- Drowsiness
- Dry mouth
- Urinary retention
- Hypersalivation
- Increased heart rate
- Rapid breathing
Rare side effects include:
- Diarrhea
- Vomiting
- Decreased appetite
- Increased appetite
How Much Benadryl Can You Give Your Dog?
The best way to determine the correct Benadryl dosage for dogs is to consult your veterinarian. The Merck Veterinary Manual recommends administering 2 to 4 milligrams of Benadryl per kilogram of body weight, two to three times a day. However, this dosage can vary depending on your dog’s age, weight, and accompanying health conditions.
It’s never a good idea to use time-release capsules for dogs, as capsules are absorbed differently in dogs compared to humans and may affect your dog’s dosage. Capsules may also break open when chewed and deliver too much medication at one time, putting your dog at risk of an overdose. Your veterinarian can prescribe diphenhydramine tablets for dogs.
Avoid using liquid Benadryl if it contains sodium, which can cause other side effects. Only use diphenhydramine products with your veterinarian’s guidance, as some human products may contain ingredients toxic to dogs, such as xylitol, alcohol, or acetaminophen. Be sure to read a product’s full ingredients list, not just the active ingredients.
Children’s Benadryl pills or tablets can be used safely if you ask your veterinarian for the appropriate dosage. If your dog refuses to take pills, your vet can also prescribe diphenhydramine liquid or flavored chews for dogs.
Is It Possible for Dogs to Have an Overdose?
Dogs can overdose on Benadryl. Signs of an overdose include hyper-excitability of the central nervous system, which can be fatal. Other warning signs to watch for are:
- Rapid heartbeat
- Dilated pupils
- Agitation
- Constipation
- Seizures
If you suspect your dog has overdosed on Benadryl, contact your veterinarian or an emergency veterinary hospital immediately. Some dogs can develop an allergic reaction to Benadryl. Seek veterinary care immediately if your dog starts having symptoms of an allergic reaction.
What Are Some Alternative Treatment Options?
Benadryl is a safe and effective medication for dogs when used as directed by a veterinarian. No natural remedies are considered to be as effective as Benadryl for reducing systemic reactions, Dr. Klein says. However, natural remedies, such as oatmeal baths, can be a useful adjunct or provide symptom relief for other kinds of allergic conditions.
For example, if your dog has a bee sting, you can make a paste of water and baking soda. “Sometimes, it can reduce the bee venom and inflammation and may extract the stinger,” he says. Here’s how to make the paste:
- Mix one teaspoon of baking soda with enough water to make a toothpaste-like paste
- Apply to the affected area
- Allow the paste to dry for about 10–15 minutes
- Lightly brush off the paste and rinse with water
Compared to Benadryl, there are stronger and more effective medications for treating your dog’s seasonal allergies, Dr. Klein says. These include prescription medications and antiseptic or medicated shampoos like those containing chlorhexidine. Similarly, there are stronger anti-nausea medications for treating motion sickness, as well as tranquilizers that can relieve your dog’s anxiety during travel and vet visits. It’s best to discuss all your options with a vet and find one that suits your dog.
Key Takeaways
- Benadryl is commonly used in dogs to treat allergic reactions, mild anxiety, and motion sickness, but should only be given under the guidance of a veterinarian.
- Certain dogs, including puppies, pregnant dogs, and those with heart disease, glaucoma, or seizure disorders, should avoid Benadryl due to the risk of serious complications.
- Always check the ingredients list before giving your dog any Benadryl product, as some formulations contain xylitol, alcohol, or acetaminophen, which are toxic to dogs.
This article is intended solely as general guidance, and does not constitute health or other professional advice. Individual situations and applicable laws vary by jurisdiction, and you are encouraged to obtain appropriate advice from qualified professionals in the applicable jurisdictions. We make no representations or warranties concerning any course of action taken by any person following or otherwise using the information offered or provided in this article, including any such information associated with and provided in connection with third-party products, and we will not be liable for any direct, indirect, consequential, special, exemplary or other damages that may result, including but not limited to economic loss, injury, illness or death.