It is a well-established fact that human medications should never be used on pets as the strength of human-grade formulations are several times higher than those designed for pets. The inherent anatomical and physiological differences between species also prevent the inter-specie use of products such that medications intended for humans should never be used on pets and vice versa. However, over the years, some human medications have been safely used in the management of health conditions in pets, especially dogs. One of these is Benadryl.

Can I Give My Dog Benadryl?

The short answer to this question is ‘Yes, you can’. However, it should only be given with the expressed recommendation of your veterinarian. Because many folks have used Benadryl to calm dog doesn’t necessarily mean that you should also do the same. Benadryl is an over-the-counter medication when bought for human therapeutic purposes. This frees it from a thorough review by the FDA for proper classification. The agency only reviews the specific active ingredients as well as the labeling of these products. In the case of Benadryl, the FDA only reviews and evaluates the therapeutic effectiveness and safety profile of Diphenhydramine, a first generation H1 antihistamine.

That being said, it should be safe to say that Benadryl is not the only drug that can be used on dogs to manage their allergic manifestations. Examples of Diphendramine-only drugs include Aler-Dryl, Diphenhist, Nytol, Syladryl, Unisom, and Sominex. Of course, there are also drugs that contain Diphenhydramine in combination with another drug such as phenylephrine, ibuprofen, naproxen, and acetaminophen, to name a few. The point is that, if Benadryl is considered to be effective in the treatment of canine allergies and to help calm dogs down because of its sedative effect, then how come only Benadryl is being used when there are other drugs in the market that contains exactly the same ingredient as Benadryl, which is Diphenhydramine?

Additionally, a review of existing literature about Benadryl confirms that all of its listed indications such as allergies, insomnia, tremors, nausea, and common cold symptoms are all geared for human health conditions. What this simply means is that Benadryl, if ever it is given for dogs, is strictly an off-the-label indication. This is why it is imperative that Benadryl be given only with the recommendation and the explicit instructions of a veterinarian. There are, however, diphenhydramine brands that are formulated for dogs and these are often labeled as “generic Benadryl”.

Again, to be blunt about it, Benadryl is just a brand name of a drug that is available in different brand names. So, if Benadryl works for dogs, then other drugs that contain Diphenhydramine should work, too.

Is it Safe?

Before we can talk about the safety of Benadryl to calm dog, it is important to understand how it works.

Diphenhydramine is one of the very first types of antihistamines that specifically targets H1 receptors in the body. Technically, it is not an antihistamine per se but rather an H1 receptor inverse agonist. What this really means is that it does not block the action of histamine on the body as what many claim it to be. Instead, it reverses the effects of histamine; that is why it is called a reverse agonist and not an antagonist nor even a blocker. Because its action on histamine H1 receptors is to reverse its effects, Benadryl can reduce the intensity of the symptoms associated with histamine-mediated allergic responses especially those that are related to the capillaries. Diphenhydramine also cross the blood-brain barrier where it also reverses the effects of H1 receptors in the brain. This is what produces its classic side effect of drowsiness or sleepiness.

Benadryl does have an antagonistic effect especially on muscarinic acetylcholine receptors, however. Now, these receptors are not histamine receptors so you cannot really call Benadryl to be an antihistamine but rather an antimuscarinic. What it does is that it competes with muscarinic acetylcholine receptors to balance acetylcholine and dopamine levels in the brain. This results in an increase in dopaminergic activity, leading to better motor control. It does have other effects, too, including the control of emesis, making it great as for motion sickness. However, it does have anticholinergic effects. These effects include:

  • Dry mouth
  • Blurred vision
  • Overheating
  • Dementia-like symptoms
  • Pupil dilation
  • Constipation
  • Urinary retention

Aside from being a reverse agonist of histamine H1 receptors and as a competitive antagonist of muscarinic acetylcholine receptors, Diphenhydramine is also a potent sodium channel blocker. Sodium channels are located in cell membranes where they facilitate the polarization of the membrane. This leads to the generation and propagation of nerve impulses. When sodium channels are blocked, sodium ions won’t be able to move into the cell and change the polarity of the membrane. This results in the cessation of nerve impulse transmission. That is why Diphenhydramine is also used as a local anesthetic. In other words, this is what calms patients – even dogs – down if they are anxious.

We mentioned above that there are actually formulations of Diphenhydramine that are combined with other drugs, mostly analgesics. This is related to the fourth action of Diphenhydramine. It is able to prevent the reuptake of serotonin into the post-synaptic neurons. This helps it to potentiate the analgesic effects of other pain relievers.

Let us try to summarize what we know so far. Diphenhydramine or Benadryl works by …

  • Reversing the effects of histamine to reduce allergy symptoms but make your dog drowsy;
  • Competing with muscarinic acetylcholine receptors to bring about muscle relaxation but with anticholinergic side effects;
  • Blocking sodium channels to minimize nerve impulse transmission and calm your dog down; and
  • Inhibiting serotonin reuptake to potentiate the effects of analgesic agents.

So, is Benadryl safe?

If the correct canine Benadryl dosage is adhered to, then the side effects can be mild to moderate, which typically include the following.

  • Urinary retention
  • Rapid breathing
  • Sleepiness or sedation
  • Hypersalivation
  • Dry mouth
  • Increased heart rate

However, Benadryl should never be given to any dog that has any of the following without first consulting a veterinarian.

  • Severe heart failure
  • Pregnancy
  • Seizure disorders
  • Acute-angle glaucoma
  • Allergic lung disease
  • Bladder neck obstruction
  • Hypertension
  • Prostatic hypertrophy

Benadryl for Dogs’ Anxiety

The use of Benadryl to calm dog is not necessarily tied strictly to its reverse histamine receptor agonistic activity. If you can remember what we explained above about the 4 different actions of Diphenhydramine, you will note that each of these can actually contribute to a more relaxed, calmer, and more peaceful dog – things that you would want to see in an anxious pooch. Let us go through them again.

  • Reverse H1 histamine agonist effect 

Diphenhydramine targets the H1 histamine receptors in the brain after passing through the blood brain barrier. This results in drowsiness or sleepiness which is a good thing if your dog is anxious. Instead of wasting its energy, it will fall asleep. This helps your pooch feel more relaxed afterwards.

  • Muscarinic acetylcholine competitive antagonistic effect 

The anticholinergic effects of Diphenhydramine can also aid in the management of canine anxiety. One of the clinical manifestations of anxiety is nausea which can actually be worsened when traveling. As dogs tend to be not really comfortable during travels with most being anxious, giving Benadryl or Diphenhydramine can help prevent nausea and bring relief to your anxious dog. Moreover, anxiety causes muscle tension. Benadryl’s anticholinergic effects can also help by providing greater control over these muscles, helping pooches relax.

  • Sodium channel blocking effect 

Because sodium ions are unable to move inside the cell to help change the polarity of the cell membrane, this effectively slows down the transmission of electrical nerve impulses. In other words, it slows down nerve impulse transmission, making your dog feel more relaxed and definitely calmer.

  • Serotonin reuptake inhibiting effect 

Serotonin is a substance that is often equated with happiness. While it is not clear whether it will have the same effects on dogs, studies show that canine well-being is also marked by increased levels of serotonin. Diphenhydramine prevents the re-entry of serotonin into the nerve endings, increasing its levels in the circulation. This helps in canine anxiety by providing affecting your dog’s mood.

Dog Benadryl Dosage Chart

The safety of Benadryl to calm dog is inherently tied to the correct canine Benadryl dosage. While the FDA does not recognize Benadryl for veterinary use, many years of trial and error have put the recommended canine Benadryl dosage to be at 1 milligram per pound of canine weight to be given every 8 to 12 hours or roughly 2 to 3 times per day.

So, if you have a pooch that weighs 30 pounds, then you can expect to give 30 milligrams of Benadryl every 8 to 12 hours. In case of severe anxiety or allergies, the dose can actually be doubled to 2 milligrams per canine body weight in pounds. Instead of giving 30 milligrams, you’ll need to give 60 milligrams 2 to 3 times per day for a 30-pound pooch.

Here’s a dog Benadryl dosage chart you can use for your pooch.

Benadryl for Puppies

Given that Benadryl is not really designed for use in dogs, there really is no way of telling whether you should give it to puppies. And even if it were possible, there is no way of telling the minimum age of puppies you can start giving Benadryl.

However, if we examine closely Benadryl in human applications, children below the age of 6 years are not advised to take Benadryl unless a pediatrician gives the go-signal to push through with the Diphenhydramine therapy. The anticholinergic effects of Diphenhydramine have been observed to cause paradoxical reactions in young children. There have also been reported cases of young children and infants losing their lives because of the misuse of Diphenhydramine.

Based on these, we can only say that it would be wiser not to give Benadryl to puppies. There are other anti-allergy medications that are specifically formulated for dogs and have been thoroughly tested to be safe. We really wouldn’t want you to risk the life of your young pooch if there are clearly other treatment options available, and better ones at that.

Where to Buy Benadryl for Dogs

You really cannot expect Benadryl to be sold in pet shops and stores since the drug is specifically made for use in human health conditions. Since it is an OTC drug, you can buy it from your local pharmacy, neighborhood convenience store, and grocery store. You don’t even need a prescription either since it’s an OTC.

The major issue we have here is that the OTC classification is based on the premise that Benadryl is going to be used for the treatment of a human health condition. It was not classified as an OTC drug to be used for dogs. In fact, even the FDA does not have a veterinary indication for Benadryl. What this simply means is that the “Benadryl to calm dog” you frequently hear about is strictly an off-the-label use. People use it for such a disease even though it is not indicated in the label.

Will Benadryl Make My Dog Sleepy?

If you have been taking down notes so far, then yes, Benadryl will make your dog sleepy. In fact, it is one of those effects of Benadryl that is often sought after by a lot of individuals whether it is going to be for themselves or for their dogs. The point is that there are at least 3 mechanisms that will make you or your dog sleep whenever you take Benadryl – the reverse agonistic activity on brain H1 histamine receptors, the anticholinergic activity on muscarinic receptors, and the nerve impulse transmission-blocking effects on sodium channels. With at least three mechanisms making sure your dog will feel more relaxed and calmer, there really is no questioning whether Benadryl will make your dog sleepy or not.

Benadryl is a drug that has antihistaminic, anticholinergic, serotonin reuptake inhibiting, and sodium channel blocking effects. Unfortunately, it is not really approved by the FDA for use in animals and as such, its use on pet dogs is more of an off-label nature. While it may be effective, there are clearly other drugs that are specific for dogs and are duly approved by the FDA for use in dogs. If you still need to give Benadryl to your dog, make sure to seek your veterinarian’s advice first.

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Olivia Williams
Olivia is our head of content for MyPetNeedsThat.com, mum of one and a true animal lover. With 12 different types of animal in her family, it's never a dull moment. When she isn't walking the dogs, feeding the cats or playing with her pet Parrot Charlie, you will find her product researching and keeping the site freshly updated with the latest products for your pets!

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