Benadryl For Dogs: Dosage, Side Effects, And Alternatives

Medically reviewed by Nicole Wanner, DVM

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Most of us will find Benadryl in our medicine cabinet. It is a widely available drug used to treat symptoms of conditions such as seasonal allergies, motion sickness, and hay fever in humans.

So, if it works for us, what about Benadryl for dogs?

You know summer holidays are not your pet's favorite time, specifically the 4th of July. Their stress then turns into your stress as you try to control the uncontrollable environment, including screaming children, intoxicated adults, and a booming firework display.

Ask around, and you will find that many dog owners have also given their dogs Benadryl to treat various conditions such as allergy symptoms, motion sickness, and even firework anxiety. In some cases, people also provide Benadryl to cats.

This popular drug is one of the few over-the-counter medications that the vet often recommends for owners to administer to their dogs and cats at home.


  • Allergies: Benadryl is a brand name for a type of drug known as Diphenhydramine – an antihistamine used to relieve symptoms of allergies, such as rashes, itching, and dog eye allergies that can come from seasonal or environmental allergens.
  • Anxiety: Benadryl contains soothing properties, which can promote calmness in dogs during high-stress situations (i.e., fireworks, thunderstorms).
  • Insomnia: For dogs with trouble sleeping, Benadryl can make your dog feel drowsy and promote sleep.
  • Itching: Diphenhydramine can decrease itching and minimize the reaction of insect bites and bee stings.
  • Motion sickness: Since the active ingredient in Diphenhydramine is similar to the active ingredient found in Dramamine (a motion sickness drug), Benadryl can be useful to treat nausea and motion sickness when traveling.

While Benadryl is FDA approved for human use, it is not FDA approved for animal use, though some types of Benadryl are considered relatively safe for dogs and cats.


  • Liquid: Benadryl is available in liquid form, but it is toxic for dogs because it contains alcohol. Therefore, you should not give it to your dog.
  • Tablet: Each Benadryl tablet contains 25 mg of Diphenhydramine. Your dog will likely hate swallowing the pill, so you might need to hide it in a delicious treat each time. Never use the time-release tablets as they are hard to dose correctly in dogs; the reason for this is that tablets are absorbed differently in dogs than in humans.
  • Children's liquid formula: If you prefer to use a liquid Benadryl, the children's formula contains no alcohol. It is also less concentrated and has a lower dosage range, which might be more suitable for owners of small dogs since it will be easier to measure out.
  • Spray: Benadryl spray can be used in emergency cases where your dog can't breathe due to swelling from insect bites and allergic rashes. However, spraying Bendaryl on open or raw wounds can sting, causing significant discomfort to your dog.
  • Topical: Benadryl also comes in gel or cream form that you can apply directly to your dog's itchy skin. Keep in mind though that irritation can occur after prolonged use. If the skin becomes infected your vet may recommend an antibiotic like Cephalexin for dogs.
  • Injection: For severe allergic reactions, your veterinarian can administer an injection of Benadryl. The treatment can be given in the muscle, vein, or under the skin.


An allergic reaction causes a chemical release of histamine in the body. Once released, histamine binds to receptors on specific cells, causing itchiness and inflammation. These receptors are known as H-1 receptors.

Benadryl (or Diphenhydramine) is an antihistamine and works by blocking the H-1 receptors and decreasing the effects of histamine.

When you give your dog Benadryl for motion sickness, it works by blocking the impulses to the vomiting center in the brain of the dog.


It is possible for dogs to overdose on Benadryl, and the symptoms can be life-threatening. If you notice any of these symptoms, contact your vet or emergency veterinary hospital immediately.

Ironically, Benadryl can cause an allergic reaction in some dogs. Just as with all drugs, you should always watch your dog closely after their first use.


As an approximate guideline, the maximum dosage of Benadryl for dogs is 1mg for every 1 pound of the dog's body weight, given 2-3 times per day, about 8-12 hours apart. Make sure that you are aware of and are OK with benadryl's known side effects before giving it to your dog.

Many factors can change this general guideline, so you should always talk to your vet to determine the proper dosage for your dog.

In general, start with a lower dose and gradually increase it until the desired effect is reached. Some dogs are more sensitive to Benadryl than others, so starting small is best.

  • Liquid: As mentioned earlier, Benadryl in liquid form is toxic to dogs because it contains alcohol; therefore, you should not give it to your dog. Instead, the Children's liquid formula is a safer choice. See the chart below.
  • Tablet: Each Benadryl tablet contains 25 mg of Diphenhydramine (1 tablet for a 25 lbs. dog), but always check the dosage on the package and never assume that every product will have the same dosage. See the chart below.

    Make sure that the Benadryl you're giving your dog contains only Diphenhydramine and is not combined with other drugs such as Tylenol as it can cause harmful side effects.
  • Topical: When applying the topical to your dog's skin, test a small area first to make sure there are no allergic reactions. Never apply gel or cream to your dog's skin if it's blistering. Overdose can happen if you are also giving your dog Benadryl tablets to treat the symptoms.
  • Injection : The injectable Benadryl is available in 10 mg/ml and 50 mg/ml. Your vet will determine the correct dosage to administer based on the symptoms.


Max Dose (every 8-12 hours) Max Dose (every 8-12 hours)
Dog Weight Tablet (mg) Children's Liquid (ml)
1 lbs – 10 lbs 1 mg – 10 mg 0.4 ml – 4 ml
10 lbs – 20 lbs 10 mg – 20 mg 4 ml – 8 ml
20 lbs – 30 lbs 20 mg – 30 mg 8 ml – 12 ml
30 lbs – 40 lbs 30 mg – 40 mg 12 ml – 16 ml
40 lbs – 50 lbs 40 mg – 50 mg 16 ml – 20 ml
50 lbs – 60 lbs 50 mg – 60 mg 20 ml – 24 ml
60 lbs – 70 lbs 60 mg – 70 mg 24 ml – 28 ml
70 lbs – 80 lbs 70 mg – 80 mg 28 ml – 32 ml
80 lbs – 90 lbs 80 mg – 90 mg 32 ml – 36 ml
90 lb – 100 lbs 90 mg – 100 mg 32 ml – 36 ml
100 lbs – 110 lbs 100 mg – 110 mg 40 ml – 44 ml
110 lbs – 120 lbs 110 mg – 120 mg 44 ml – 48 ml
120 lbs – 130 lbs 120 mg – 130 mg 48 ml – 52 ml
130 lbs – 140 lbs 130 mg – 140 mg 52 ml – 56 ml
140 lbs – 150 lbs 140 mg – 150 mg 56 ml – 60 ml


It usually takes 24 hours for Benadryl to wear off and stop working. However, for dogs with liver or kidney disease, the effects can last longer. Always talk to your veterinarian before giving Benadryl, especially if your dog has chronic liver, kidney, or heart problems.


Benadryl side effects in dogs are similar to those in humans. Common side effects include dry mouth, sleepiness, and urine retention.

Some dogs may experience rare side effects, such as diarrhea, vomiting, rapid breathing, increased heart rate, and appetize changes. If these symptoms become severe, you should call your vet.

Dogs with the following conditions should not take Benadryl without first consulting with the vet:

  • Allergic lung disease
  • Bladder neck obstruction
  • Cardiac conditions (such as cardiovascular disease, heart failure)
  • Pregnant or nursing
  • Glaucoma
  • High blood pressure
  • Hypertension
  • Hyperthyroidism
  • Low blood pressure
  • Prostatic hypertrophy
  • Seizure disorders


Benadryl can reduce the effectiveness of prokinetic drugs (metoclopramide, cisapride) used for constipation and other GI problems.


If the side effect of Benadryl, like dry mouth, sleepiness, and urine retention, concern you, or if your dog suffers from the conditions mentioned above, there are natural alternatives to Benadryl available.

  • Allergies/Antihistamines - Allergy symptoms include sneezing, itching, and cold-like symptoms. Histamine is the part of the immune system that causes symptoms. Antihistamines work by stopping histamine activity. Some of the more popular natural antihistamines are Stinging Nettle, Quercetin, and some foods like fresh meats, fish, eggs, and non-citrus fruits. There is also some evidece that CBD might help with seasonal allergies and itching
  • Motion Sickness – Herbs like Ginger, Peppermint, Catnip, Fennel, and Dill have compounds that produce anti-nausea effects, which may improve reactions to motion sickness.

    Research has also shown CBD oil for dogs may be an effective anti-vomiting compound. A 2001 article from the American Gastroenterological Association said researchers found data consistent with the hypothesis that cannabinoids act centrally to inhibit the act of vomiting.
  • Anxiety – Natural solutions for anxiety are exercise, essential oils, grooming, music, pheromones, massage, and supplements. You can also use CBD oil to promote calming. In lab models, CBD has been shown to reduce nervous behaviors in humans, mice, and rats. These results are a good sign for dogs as the Endocannabinoid systems closely match in mammals.

A veterinary journal published a canine study that shows the effect of cannabidiol (CBD) on the canine inflammatory response. The results showed that CBD reduced the inflammatory response in proteins of immune system cells. While this is a small study, it is a good indication for those of us that want to avoid the side effects of Benadryl.

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