How to Use Benadryl for Dogs Safely

Published November 16, 2021
Woman hand holding pills and close-up dog

If you've been instructed to give your dog Benadryl, you want to ensure that you do so safely. Understanding how Benadryl works, when to avoid giving it to your dog, and the potential side effects, is a great start. Feel confident with this comprehensive guide to Benadryl for dogs.

Uses of Benadryl in Dogs

Diphenhydramine, most commonly known by the brand name Benadryl, is an antihistamine medication that works to block the effects of histamine. There are several reasons a dog may be advised to take it.


Just like in humans, Benadryl can be effective at reducing the symptoms associated with allergies. It can provide pets with relief from itchy or red skin, sneezing, and watery eyes, among other signs. Some dogs must take an antihistamine seasonally or continuously for their allergies.

Mild Allergic Reactions

Mild allergic reactions like those from bug bites can often be managed with a dose of an antihistamine medication. Benadryl is also commonly used to pre-treat dogs who experience mild vaccine reactions. However, in the case of a severe anaphylactic reaction, dogs require urgent veterinary care.

Motion Sickness

Dog looking out of car window at coastline

Benadryl can be helpful in preventing motion sickness when given at least 30 minutes prior to a car ride. Keep in mind, this drug might not be ideal for long road trips as the effects only last about 3 to 6 hours and Benadryl can't be re-dosed any sooner than every 8 hours.

Cancer Management

Mast cell tumors (MCT), a type of cancerous skin growth, release histamines when agitated. An antihistamine medication such as Benadryl can help combat this. Many veterinary oncologists recommend Benadryl prior to surgical removal of MCTs or may put these patients on it as part of long-term management.


Some dog owners choose to use Benadryl to calm their pet's anxiety. Although this medication can cause drowsiness as a side effect, studies suggest that it is not an effective sedative. In fact, higher doses can elicit the opposite result by causing excitement in some dogs. Speak to your veterinarian before using Benadryl for anxiety; there are likely more effective solutions available that are still safe for your dog.

How to Safely Administer Benadryl

Always check with your veterinarian before offering your dog any type of medication, whether it's an over-the-counter drug, old prescription, or was prescribed to another pet. Be sure to use the correct dose based on your dog's current weight. Know that it takes approximately 30 to 60 minutes to take effect.

Benadryl is most commonly found as 25 or 50 mg tablets, although your veterinarian may carry a pet-specific product with a lower concentration, such as 10 mg. This can be especially helpful when medicating smaller dogs or dogs who require irregular dosages. Many of these medications are also flavored for easy administration.

If you do elect to get your dog's Benadryl at your pharmacy instead, keep in mind that human forms of this medication often contain ingredients that are toxic to dogs. Purchase products with the only active ingredient listed as "diphenhydramine HCl." Avoid any decongestant or pain relief-type formulas containing drugs like acetaminophen or phenylephrine. Liquid formulas are also made up of alcohol, which is toxic to dogs. However, children's liquid varieties that contain no alcohol may be safe if they are also free of xylitol.

Pharmacist hand taking medication from drawer

Potential Side Effects to be Aware of

As with any drug, Benadryl can have possible side effects in dogs. Most will appear within one hour after administration.

  • Drowsiness
  • Excessive drooling
  • Panting
  • Increased heart rate
  • Urinary retention
  • Vomiting
  • Diarrhea
  • Changes in appetite

When to Avoid Giving Your Dog Benadryl

Although Benadryl is tolerated well by most pets, dogs with the following conditions should use extreme caution before taking Benadryl.

  • Hypothyroidism
  • Epilepsy
  • Glaucoma
  • High blood pressure
  • Heart disease
  • Prostate issues
  • Pregnant dogs
  • Young puppies
  • Dogs on other medications, including Amitriptyline, Atropine, or any sedation/pain medications.

Signs of Benadryl Overdose

Vet and Labrador retriever

Even though its use is relatively safe, it is possible for a dog to experience life-threatening symptoms in response to higher concentrations of Benadryl. Dogs with existing diseases are at higher risk of overdose.

  • Excitability or agitation
  • Aggression
  • Extreme lethargy
  • Dilated pupils
  • Racing heartbeat
  • Difficulty breathing
  • Muscle tremors
  • Seizures

If your dog ingests a high volume of Benadryl or exhibits any concerning symptoms of overdose, contact your veterinarian or an animal poison service right away. Likewise, if the medication contains any toxic ingredients like acetaminophen, phenylephrine, xylitol, or alcohol, seek urgent care.

Can I Give my Dog Benadryl?

Benadryl is considered a safe and useful medication that many pet owners give their dogs. Always speak with your vet before administering Benadryl. If your dog becomes slightly drowsy on this medication, there's likely no need to be alarmed, but be mindful to monitor for any concerning side effects and seek help as needed.

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How to Use Benadryl for Dogs Safely