The temptation to reach into our medicine cabinets to treat our pets can be very dangerous. Humans and dogs react very differently to medications, which is why veterinarians caution dog owners against making independent decisions about how to medicate their animals. However, some human medications are safe for use with dogs, as long as they are used appropriately.
Veterinarians use diphenhydramine, commonly known by the brand name Benadryl, for dogs on a regular basis to treat allergies, travel anxiety, and motion sickness. While you should always consult with your veterinarian before giving your dog a human medication, here is what you need to know about using Benadryl for dogs.
What Is Benadryl?
Benadryl is the brand name for the active ingredient diphenhydramine HCL. Diphenhydramine is a first-generation ethanolamine-derivative antihistamine, which is the scientific way of classifying antihistamines that can cross the blood-brain barrier from those that cannot. The ability to cross the blood-brain barrier makes them very effective, but also increases the risk of adverse effects when compared to less effective second-generation antihistamines. While Benadryl is not yet FDA-approved for veterinary use, it is considered safe for use in dogs and cats and is commonly used in veterinary practices across the U.S.
How Does Benadryl Work?
Diphenhydramine is a receptor antagonist, which means that the drug works by blocking the receptors that receive histamines in the body. This relieves many of the symptoms associated with allergies, like itching, sneezing, and hives. The body still produces histamines, but the receptor antagonist blocks the receptors from registering the histamines. It is a bit like the mail-person trying to deliver mail to an already full mailbox. The letter arrives, but there is no room for it.
What Does Benadryl Treat in Dogs?
Benadryl is a great medication for use in dogs with mild-to-moderate allergies. Seasonal allergies, food allergies, environmental allergies, and allergic reactions to snake and insect bites all respond to Benadryl in most cases. Benadryl is commonly used to treat itchiness in dogs caused by skin allergies, and it also reduces many of the other symptoms of allergies, including:
- Swelling and inflammation
- Runny nose and eyes
- Anaphylactic reaction
One of the side effects of Benadryl is drowsiness, which helps to calm anxious dogs. The Merck Veterinary Manual states that diphenhydramine may relieve symptoms of mild-to-moderate anxiety in pets associated with travel. It also may help relieve motion sickness during car rides and plane rides.
Veterinarians prescribe Benadryl for dogs with mast cell tumors to help mitigate the effects of the massive histamine release caused by mast cell degranulation. Benadryl is also used as adjunct therapy for other conditions. Veterinarians sometimes prescribe diphenhydramine during heartworm treatment, as it helps prevent allergic reactions associated with heartworm treatment therapy.
Benadryl makes an excellent addition to your pet emergency kit. If you don’t already have a pet emergency kit or pet travel kit, consider putting one together today.
When to Ask Your Vet About Benadryl for Dogs
Before you reach for the Benadryl, consult your veterinarian about your dog’s symptoms. Allergy symptoms like itching and red eyes are also signs of more serious conditions. In some cases, like glaucoma, giving your dog Benadryl can actually worsen your dog’s condition. Red, goopy eyes could be a symptom of allergies, or it could also be a sign of an eye disease like glaucoma or dry eye, which Benadryl will not help treat. Similarly, itching is frequently associated with both allergies and other skin conditions. As Benadryl is ineffective for treating certain skin diseases, it is always a good idea to consult with your veterinarian to make sure you are doing the best thing for your dog’s health.
Your vet may recommend you bring your dog in for a checkup. If you choose not to bring your dog in against your veterinarian’s advice, or if you administer Benadryl without first consulting your veterinarian, be sure to keep a close eye on your dog and call your vet if your pet’s condition worsens.
Side Effects of Benadryl
There are side effects associated with using Benadryl for dogs that all dog owners should be aware of. Just like people check with their doctors before taking a new medication, you should always check with your veterinarian before introducing Benadryl to see if it has any potential drug interactions with your dog’s other medications, or if it could worsen a preexisting condition.
If your dog has any of the following conditions, only use Benadryl after consulting your veterinarian:
- Angle closure glaucoma
- Severe heart failure
- Prostatic hypertrophy
- Bladder neck obstruction
- Seizure disorders
- Allergic lung disease
Common side effects associated with using Benadryl for dogs include:
- Dry mouth
- Urinary retention
- Increased heart rate
- Rapid breathing
Rare side effects:
Most side effects occur within the first hour of exposure, so monitor your dog carefully during this time.
It is possible to overdose on Benadryl. Signs of an overdose include hyper-excitability of the central nervous system (CNS) and can be fatal. Other warning signs to watch for are:
- Rapid heartbeat
- Dilated pupils
If you suspect your dog has overdosed on Benadryl, contact your veterinarian or emergency veterinary hospital immediately.
Some dogs develop an allergic reaction to Benadryl. If your dog starts having symptoms of an allergic reaction, seek veterinary care immediately. As Benadryl for dogs is often used to treat allergies, keep an eye on your dog after giving Benadryl for the first time to make sure that the allergy symptoms don’t worsen.
Dosage of Benadryl for Dogs
The best way to determine the correct Benadryl dosage for dogs is to consult your veterinarian. The Merck Veterinary Manual recommends administering 2-4mg of Benadryl per kilogram of body weight, two to three times a day. However, this dosage can vary depending on your dog’s existing medical conditions.
Never use time-release capsules for dogs, as capsules are absorbed differently in dogs than in humans and may affect your dog’s dosage. They may also break open when chewed and deliver too much medication at one time, putting your dog at risk of an overdose. If you choose to use a liquid Benadryl, it is safer to use a children’s liquid formula, as most do not contain alcohol (although they do contain sodium). Children’s Benadryl pills or tablets can also be used to dose very small dogs. Dosage for liquid Benadryl is different than the dosage for Benadryl pills. Consult your veterinarian for the appropriate dosage, and use a syringe to increase measurement accuracy and ease of administration.
Benadryl typically takes 30 minutes to start working, so plan accordingly if you plan on using it to treat anxiety or mild motion sickness. For dogs with chronic allergies or conditions that require daily doses, consult your veterinarian about the appropriate dosage, as it may change over time.
Always consult your veterinarian before giving Benadryl to pregnant or nursing dogs, since the drug is not recommended for use in these animals.
Is Benadryl Safe for Your Dog?
Benadryl is a relatively safe and effective medication for dogs when used according to the instructions of a veterinarian. As with any new medication, always observe your dog closely after administration to make sure your dog does not suffer any adverse reactions. If you have any further questions about Benadryl for dogs, contact your veterinarian for more information.