Even though Benadryl is designed for use in humans, veterinarians often prescribe this medication to dogs for seasonal allergies, motion sickness, and long-term management of mast cell tumors, among other things. It's helpful to understand the correct dosage of Benadryl for dogs, the potential side effects, and the many uses of this drug to keep your pet safe when giving it.
Is Benadryl Safe for Dogs?
Yes, Benadryl is safe for most dogs and is actually prescribed by veterinarians for a wide range of conditions. You might see it listed as diphenhydramine, which is the generic name for the drug, as opposed to the brand name Benadryl. But don't worry; it's the same thing.
Benadryl Dosage Chart for Dogs
The recommended veterinary dosage of Benadryl (diphenhydramine) is 2 to 4 milligrams for every kilogram of body weight, which can be given every 8 to 12 hours, or twice to three times daily. An easy way to calculate this at home is to give 1 milligram for every 1 pound of body weight, or use the guidelines below for low and high dose ranges.
This chart is not intended to replace veterinary guidance. Consult with your veterinarian to confirm that Benadryl is suitable for your pet prior to administration.
| Weight (pounds) | Amount of Benadryl (milligrams) |
| 10 lbs | 10 to 20 mg |
| 20 lbs | 18 to 36 mg |
| 30 lbs | 27 to 54 mg |
| 40 lbs | 36 to 72 mg |
| 50 lbs | 45 to 90 mg |
| 60 lbs | 54 to 109 mg |
| 70 lbs | 63 to 127 mg |
| 80 lbs | 72 to 145 mg |
| 90 lbs | 81 to 163 mg |
| 100 lbs + | 90 to 180 mg |
How to Dose Benadryl
Benadryl typically comes in 25 mg and 50 mg tablets. If your dog is between doses or should receive a half or quarter tablet, use a pill cutter or blade to split the medication. For example, a 10-pound dog should receive 10 to 20 mg, which means ½ of a 25 mg tablet (equivalent to 12.5 mg) would be an appropriate dose for them.
Benadryl takes about 30 to 60 minutes to start working in dogs.
Precautions Before Giving Benadryl to Dogs
Not so fast! Even with the correct dosing information, you'll want to take these precautions before giving your dog Benadryl.
- Contact your veterinarian. Always speak with your vet before giving your dog any medication. They know your dog's medical history and can give you the most accurate dose. Benadryl is not safe for dogs with certain conditions and can interact with other medications.
- Confirm the ingredients. Purchase Benadryl directly from your veterinary hospital or select a product containing only diphenhydramine, since common additives and flavorings can be toxic to dogs. Avoid liquid products containing alcohol or xylitol as well as decongestant formulas with ingredients like phenylephrine or acetaminophen.
- Asses your dog's condition. If your dog is suffering from an allergic reaction, particularly if they are having trouble breathing, experiencing vomiting, facial swelling, or pale gums, seek urgent veterinary care. Oral Benadryl doesn't take effect until about 30 minutes or longer after ingestion, which could be too late in these cases.
- Know your dog's weight. While an adult human can take a standard dose of Benadryl, dogs come in a vast range of sizes. The right dose depends on their weight. If you do not have a recent weight for your dog or suspect that they may have gained or lost some weight since you weighed them last, hop them up on the scale.
Potential Side Effects
As with any drug, Benadryl can have possible side effects in dogs. Most will appear within an hour of them taking it.
- Drowsiness
- Excessive drooling
- Panting
- Increased heart rate
- Urinary retention
- Vomiting
- Diarrhea
- Changes in appetite
Benadryl can cause drowsiness in dogs, which is why people sometimes give it before fireworks or a thunderstorm. Just remember, Benadryl doesn't reduce anxiety, so take other steps to calm your dog's nerves.
Can Dogs Overdose on Benadryl?
Even though Benadryl is a fairly safe drug for dogs, it is possible for them to get too much. Dogs with existing diseases are at a greater risk of overdosing, but any dog can experience life-threatening symptoms in response to high concentrations of the medication. Signs of Benadryl overdose include:
- Excitability or agitation
- Aggression
- Extreme lethargy
- Dilated pupils
- Racing heartbeat
- Difficulty breathing
- Muscle tremors
- Seizures
If your dog takes a high dose of Benadryl or shows any of the signs 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.
The American Society for the Prevention of Cruelty to Animals offers an animal poison control service by calling 888-426-4435. The Pet Poison Helpline is also available at 855-764-7661. Fees may apply.
When Is it a Good Idea to Give Your Dog Benadryl?
Benadryl is kind of a wonder drug in that it can be used for several different things. Of course, its main use is as an antihistamine, but it has many other properties (like anti-nausea abilities; who knew?!) that can help dogs in other situations.
1. Allergies
Just like in humans, Benadryl can reduce the symptoms associated with allergies. If your dog experiences itchy or red skin, sneezing, or watery eyes because of allergies, Benadryl might help. Some dogs take year-round or just seasonally for their allergies.
2. Car Sickness
Does your dog get car sick? Benadryl can be helpful in preventing motion sickness when given at least 30 minutes prior to a car ride. Just keep in mind, it might not be ideal for long road trips because the effects only last about 3 to 6 hours, and Benadryl can't be re-dosed any sooner than every 8 hours.
3. 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 used to pre-treat dogs who experience mild vaccine reactions. However, in the case of a severe anaphylactic reaction, dogs require urgent veterinary care.
4. Cancer Management
Mast cell tumors (MCT), a type of cancerous skin growth, release histamines when agitated, so an antihistamine medication like Benadryl can help combat this. Most veterinary oncologists recommend Benadryl before surgery or as part of a long-term management plan.
The Benadryl dosage for mast cell tumors in dogs is generally the same 2 to 4 milligrams per kilogram of body weight, but it can vary depending on what other medications your dog is on. Ask your oncologist for guidance if you're unsure.
When Not to Give Your Dog Benadryl
Even though most dogs do very well with Benadryl, it can be dangerous for some. 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, like amitriptyline, atropine, or any sedation or pain medications.
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 and if your dog becomes slightly drowsy on this medication, don't be alarmed. Just make sure to monitor for any concerning side effects and avoid formulas that contain ingredients other than diphenhydramine.
