Benadryl is an over-the-counter medicine that can be given to dogs. Diphenhydramine, the most common active ingredient, is an H1 antagonist, which means it helps to prevent the uptake of histamine (a type of substance responsible for allergic reactions) by receptors in the body. This relieves inflammation, watery eyes and many other allergy symptoms. Sleepiness is a common side effect which is why diphenhydramine is also the active ingredient in popular sleeping aids such as Sominex and Nytol.

Benadryl is not yet FDA-approved for use in animals, but is considered quite safe when used correctly and with approval from your vet.

Remember: Benadryl is the brand name and not the name of the drug which produces the effects. Make sure the formulation you’re using only contains active ingredients which are safe for dogs such as diphenhydramine or cetirizine. In some countries outside of the States, diphenhydramine is no longer used in Benadryl products. For example, in the UK most Benadryl allergy products contain cetirizine instead. To see which active ingredients a product is using you should read the packaging, the main ingredients are usually displayed clearly on both the front and back of the box.

Natural Remedies:

Many people stand by the ability of natural remedies to soothe their dog’s symptoms. Benadryl can be safe when used correctly, but it does have some risks, complications and adverse effects, while the following natural alternatives offer a much safer solution.

Anxietrex – A completely safe remedy for anxiety in dogs. Free from side effects and suitable for dogs of all ages.

Derma-Ionx – With zero side effects, Derma-Ionx treats skin irritation (including allergic conditions) and itching in dogs of any age.

Benadryl Dosage For Dogs

 
The usual dosage of Benadryl for dogs is 1 mg/lb every 8 to 12 hours (two to three times daily). This suggested dose is for formulations containing diphenhydramine as the only the active ingredient. In certain situations (e.g. following a snake bite) 2 mg/lb per dose may be given instead. When used for allergies, it is best if the medicine is given before exposure to the allergen.

Don’t give any amount to your dog without checking with your vet first, as the dosage can differ depending on several factors including your dog’s medical history. It’s also important to determine the cause of symptoms before administering the medicine. When treating a small dog it’s better to use the children’s formula which contains smaller amounts of active ingredient, making it easier to measure out an accurate dose.

Giving the medicine on an empty stomach is fine, but giving it with food can help to prevent drooling and vomiting.

The chart and calculator below will help you find the usual dosage for your dog.
 

Chart of the usual diphenhydramine dosage for a dog
Dog’s weight in pounds: Dosage in mg:


When used on a long-term basis (which is often the case when treating allergies), the effectiveness of diphenhydramine can diminish, so it’s best to rotate through different antihistamines in this case. Cetirizine, loratadine and chlorpheniramine are just a few examples of common antihistamines which work well for allergies.

How long does it take to start working?

Diphenhydramine takes about 30 minutes to start working. If you’re using it to treat anxiety in dogs or to prevent motion sickness, administer the medicine 30 minutes before the stressful event or journey is expected.

 

Dye-free formulaLiquid:

If you decide to use the liquid, use the children’s liquid formulation (preferably the dye-free version), which should not contain alcohol or xylitol – be sure to check the ingredients on the box to confirm this. At the standard concentration, every 5 mL of liquid contains 12.5 mg of diphenhydramine and can be given at a dosage of 0.4 mL/lb.

For reference, a standard US teaspoon measurement is 5 mL. You can use a syringe to increase the accuracy of the dose and to make things easier when delivering larger amounts.

Unfortunately most dogs dislike the taste of liquid Benadryl, so it is better to use tablets if possible.

Use the calculator below to find the typical dosage for your dog:
 

Dog’s weight in pounds: Dosage in mL:

 
Some formulations may use a concentration of 6.25 mg per 5 mL, which means you will have to use twice as much as normal.

 

Topical:

Benadryl is also available in the form of cream, gel, stick, or spray, usually containing 1% diphenhydramine (or 2% in the extra strength formula), which can be applied topically 2 – 3 times daily. The local anesthetic properties of the drug can help to reduce itching.

Many people forget that they are using medicines when applying topical products, but even though little is absorbed meaning side effects are rare, applying far too much can lead to overdose symptoms just as though you had used too many tablets or too much liquid. This danger can soon add up if you have also given your dog Benadryl tablets/liquid, or other antihistamine products.

There are several topical diphenhydramine products made specifically for animals including Atopicream® and Benasoothe®.

The gels and creams are often applied up to three times a day, while the shampoos and the conditioners are usually only used once a day or once a week. If you are using shampoo/conditioner you should leave it on your dog for at least 10 minutes before washing it off.

Keep in mind that using topicals can sometimes cause irritation or sensitivity at the application site(s), especially through prolonged use. Topicals should never be applied to blistered patches of skin.

Warning: Avoid the Benadryl “Itch Cooling Gel” which contains camphor, as this substance is poisonous to dogs.

 

Injectable:

Sometimes it will be necessary for a veterinary professional to give your dog diphenhydramine by injection, especially when the airway is blocked due to a severe allergic reaction, or when the effects are needed quickly. In this case, 0.25 – 1 mg/lb may be injected into muscle tissue, into the blood stream, or under the skin.
 

Example: A dog weighing 25 pounds would require 25 mg (one regular strength pill) of Benadryl with the active ingredient diphenhydramine up to three times daily.


Other Active Ingredients:
 
Some Benadryl products contain active ingredients other than diphenhydramine. These may also be safe for use in dogs, but won’t always treat the same conditions.

Cetirizine

Formulations containing cetirizine are indicated for use in the treatment of dermatitis. The dosage per day is typically as follows:
 

Weight of dog

Dosage of cetirizine

0 – 15 lbs 5 mg (½ tablet)
16 – 39 lbs 10 mg (1 tablet)
40 lbs + 15 mg (1½ tablets)

 
According to one study, a dosage of 0.45 mg/lb (1 mg/kg) once daily was sufficient to control itching in 18% of treated dogs.

Because cetirizine rarely causes sedation, it is not as effective for preventing anxiety during storms, fireworks or other stressful events.

Acrivastine

Formulations containing acrivastine also contain pseudoephedrine which can be dangerous in high doses. For this reason, products containing acrivastine should be avoided.

Pholcodine

“Benadryl Dry, Tickly Cough” is a popular cough mixture. Each mL of this medicine contains 1 mg of pholcodine. Pholcodine is sometimes dosed at around 0.05 – 0.09 mg per pound of body weight (0.05 – 0.09 mL of mixture per pound) to relieve symptoms of coughing, but is rarely used to treat dogs, and it’s best to double check with a vet before use. Robitussin-DM which contains dextromethorphan is more common choice for the treatment of coughs.
 

Can I Give My Dog Benadryl?

 
Several different forms of Benadryl are safe to give to a dog, however the most commonly used form of this medicine (and the one most people will be familiar with) contains diphenhydramine.

It’s important to avoid using liquid mixtures that contain ingredients unsuitable for dogs. As an example, xylitol is a common additive that can become toxic to dogs in large amounts, and it’s important to avoid formulations with a high alcohol content. The children’s Benadryl liquid mixture is free from both alcohol and xylitol.

Below are some of the dog-safe active ingredients you can find in Benadryl products. Be sure to stick to formulations containing these ingredients (remember, the active ingredients will be displayed clearly on the packaging).

Diphenhydramine

Diphenhydramine is most commonly used for treating allergies, anxiety, and motion sickness. Though it has not yet been approved by the FDA for use in animals, it is very commonly used in veterinary practice, and is often safe for treating dogs at the 1 mg/lb dosage recommended earlier.

Cetirizine

Cetirizine is sometimes prescribed by vets for the treatment of itching. Cetirizine doesn’t cross the blood-brain barrier in large amounts, meaning there are generally fewer side effects.

Pholcodine

In studies, pholcodine was given to 12 dogs at doses of up to 150 mg/kg without fatality. However, amounts of 300 mg/kg caused death in one of the two dogs who received it. At the very low doses recommended for use in dogs, it is likely to be safe.

Safety Guidelines

 
Always consult with your vet before giving medicine to your pet, and avoid using time-release capsules made for humans. Because of a dog’s anatomy these capsules are not usually digested fully when swallowed whole. To help the vet decide whether your pet is suitable for treatment, be sure to tell them:
 

 
Dogs with heart disease, angle-closure glaucoma, hyperthyroidism, and prostate enlargement could react badly to diphenhydramine. If you’re using the cetirizine formula, dogs with kidney or liver disease are at a higher risk of complications.

Avoid using with other anticholinergic drugs, as this could lead to symptoms of toxicity. Combining diphenhydramine with depressants is likely to cause stronger sedation. There are also a few other medicines that can react with diphenhydramine.

Pregnancy & Nursing Warning: Diphenhydramine is not recommended for use during pregnancy (especially when the animal is near term), though your vet may advise otherwise under specific circumstances. It is to be avoided or used with caution in nursing dogs, especially with newborn pups, as the drug is passed in milk.

What Is It Used For In Dogs?

 
There are several important uses of Benadryl for dogs, most commonly it is used to treat allergies and insect stings, but its possible uses also depends on the active ingredient. Below lists the uses of each different dog-safe active ingredient.

Diphenhydramine:
 

  • Allergies and reactions to vaccines
  •  

    Histamine is a type of substance that plays a role in allergic reactions. When the body detects an allergen, it releases histamine which is then picked up by receptors in the body, causing many dreaded allergy symptoms. By helping to prevent the receptors from picking up histamine, the symptoms of allergies can be avoided.

     

  • Insomnia
  •  

    Diphenhydramine doesn’t only block the uptake of histamine, it also helps to block another chemical known as acetylcholine. This is what causes the sleepiness. If the medicine is used very frequently, its effectiveness at promoting sleep can become reduced. Melatonin is more commonly used for this purpose.

     

  • Vomiting and motion sickness
  •  

    Diphenhydramine is very similar to dimenhydrinate, the active ingredient of Dramamine. It can help to prevent feelings of nausea and travel sickness.

     

  • Stings and bites
  •  

    Bites or stings from certain creatures such as bees can also release histamine. Using an antihistamine like diphenhydramine can help to reduce discomfort and swelling. Be careful, though, if a dog is very sensitive to the venom the airway may become constricted. Trying to give him medicines by mouth at this point can be dangerous.

    This post by Dr. Jason Nicholas contains more information about treating stings with Benadryl, as well as a few home remedies you can try.

     

  • Anxiety (during July fireworks for example)
  •  

    The sedative properties of the medicine can help a dog to stay calm through situations that would usually make him nervous, for example during fireworks or visits to the vet.

     

  • Itching (particularly with topicals)
  •  

    Diphenhydramine can be used to treat itching related to dermatitis, but cetirizine and glucocorticoids such as cortisone tend to be more effective. Topically, however, the drug has slight anesthetic properties which can help to reduce itching.

     

  • Mast cell tumors
  •  

    It is not used to cure the tumors, but can reduce the dangerous effects associated with the increased release of histamine in the body. This helps to control blood pressure and appetite loss.

 
If you aren’t sure whether this medicine is the right choice, there are other options your vet can discuss with you. Ask them about Claritin and chlorpheniramine, two other medicines which are commonly used for treating allergies. For motion sickness you could also try Dramamine with dimenhydrinate. Dimenhydrinate is almost the same exact substance as diphenhydramine, except it is bound to a mild stimulant to prevent drowsiness while still providing effective relief from nausea.

Cetirizine:
 

  • Allergic dermatitis
  • Atopic dermatitis

 
Cetirizine is most often used to treat allergies affecting the skin.
 
Pholcodine:

Pholcodine is sometimes used in dogs to help control coughing.
 

Side Effects

 

Sleepiness is very common when using diphenhydramine, but this can reduce over time with continued use.

Dogs who receive diphenhydramine could experience a number of adverse effects. It’s common for them to behave strangely or to seem a bit “spaced out”, but they can also experience:
 
Common
 

  • Sleepiness
  • Dry mouth
  • Urinary retention
  • Sluggish reactions

 
Less Common
 

  • Diarrhea
  • Vomiting
  • Loss of appetite
  • Allergic reaction

 
The drowsiness associated with diphenhydramine may reduce over time with continued use. However, the sedative properties may affect the performance of working dogs, making it an unsuitable choice.

Dogs who receive cetirizine may vomit or salivate excessively, but because it doesn’t cross the blood-brain barrier as readily, unwanted effects such as drowsiness should not occur.

If serious adverse effects begin to develop, for example an allergic reaction, seek immediate veterinary care. Look out for typical allergy symptoms such as itching, difficulty breathing, rashes, hives, rapid heartbeat, and sneezing. Severe cases should be treated as medical emergencies.


Overdose:

Though it’s often safe to use diphenhydramine for allergies, anxiety, and a variety of other conditions, an overdose could be dangerous. Despite the potential dangers, dogs have survived (with hospitalization) up to 16 times greater than the recommended dose, so if you act fast, recovery is likely. Overdose symptoms may include muscle tremors, a rapid or irregular heartbeat, breathing difficulties, extreme fatigue, confusion, and a high temperature. High blood pressure is also possible following an overdose, which could lead to circling, seizures, and disorientation among other signs.

If you suspect an overdose. seek immediate veterinary care or call the ASPCA poison control hotline on (888) 426-4435. Do not attempt to make your dog vomit unless you have been instructed to do so by a professional.

Diazepam and barbiturates are unsuitable for treating seizures caused by overdose, instead, an IV injection of phenytoin is recommended. Other treatments for overdose includes inducing vomiting (if the dog is stable), and following this, the use of activated charcoal.
 

More Information

 
We recommend watching this helpful video by Dr. Greg Martinez, it contains great information about giving Benadryl to dogs and how it can be used to treat allergies:
 

 
Sources

Dr. H. Peikes
Plumb’s Veterinary Drug Handbook (sixth edition)