Can I Give My Dog Benadryl? Vet Advice, Benefits & Dangers

This content was reviewed and fact-checked by veterinarian Dr. Aukse Caraite, DVM.

Yes, dogs can take Benadryl in moderation, and this common over-the-counter medication can offer some health benefits—particularly for allergies, itching, and even motion sickness. However, before giving your dog Benadryl, several important factors must be considered. While plain Benadryl (diphenhydramine) without added ingredients is generally safe, some formulations—like those containing alcohol, decongestants, or artificial sweeteners such as xylitol—can harm dogs. Plus, what about dosage based on your dog’s weight and size? Can too much Benadryl cause side effects like drowsiness or dry mouth? This guide will explore the benefits, potential risks, proper dosage, and the safest way to give Benadryl to your dog.

What Is Benadryl?

Benadryl is the brand name for diphenhydramine, an over-the-counter antihistamine commonly used to relieve allergy symptoms in humans—and, under veterinary guidance, it can also be safely used for dogs. Its active ingredient, diphenhydramine, is a first-generation H₁-antihistamine that works by blocking the effects of histamine, a substance in the body that causes allergic symptoms.

Component Analysis

Here is a breakdown of all the ingredients in Benadryl tablets and their safety for dogs.

What Is Benadryl Used For In Dogs

While it is not FDA-approved for veterinary use, it is widely considered safe and effective when administered under veterinary guidance.

What The Science Says

Here is what research says about the claimed benefits and uses of Benadryl for dogs

• Antihistamine (anti-allergic) properties of Benadryl: A study published in The Journal of Pharmacology and Experimental Therapeutics found that Benadryl significantly reduced histamine-induced muscle spasms and blood pressure drops, even at highly diluted doses. Although results were mixed, it also showed potential to reduce gastric acid secretion triggered by histamine. Importantly, Benadryl does not interfere with emergency medications like epinephrine and may actually enhance their effects, reinforcing its safety and reliability for managing mild allergic reactions in dogs. ^[1]
• Reduces allergic shock: Dogs that were given Benadryl intravenously (10 mg/kg) prior to allergen exposure experienced significantly fewer fatal reactions—showing zero deaths in 22 treated dogs compared to 9 deaths in 26 untreated controls.^[2] These findings support that Benadryl can effectively reduce the severity of anaphylaxis shock, a severe, life-threatening allergic reaction.
• ​Reduces vomiting: ​Researchers discovered that administering Benadryl before giving apomorphine—a drug known to induce vomiting—significantly reduced the likelihood of vomiting.^[3] This suggests that Benadryl can be effective in preventing nausea and vomiting in dogs, particularly in situations like motion sickness or after ingesting substances that might cause vomiting.
• More beneficial than other antihistamines: A study compared Benadryl to two other antihistamines—Pyribenzamine and Neoantergan—in dogs. It was found that all three drugs worked equally well in blocking the blood pressure-lowering effects of histamine. However, only Benadryl reduced the effects of another chemical called acetylcholine, showing it may have broader actions. Benadryl helped relax the intestines in dogs, while the other two drugs affected other organs like the uterus and small intestine differently. Additionally, all three antihistamines made the body respond more strongly to epinephrine (adrenaline), which could help treat allergic reactions.^[4]

Safety Guidelines & Rules

Benadryl (diphenhydramine) is generally safe for dogs when used correctly, but there are important safety rules to follow.

1. Consult Your Veterinarian

Before administering Benadryl, please seek professional advice to determine whether it’s appropriate for your dog’s health needs. If you can’t reach your vet, you can chat live with a registered online veterinary professional via our online vet chat or video chat support (24 hours a day, 7 days a week).

2. Use Dog-Friendly Benadryl

Ensure the product contains only diphenhydramine without additional active ingredients like decongestants or alcohol, which can be harmful to dogs. For example, Benadryl Allergy Ultratabs (must say ONLY active ingredient: Diphenhydramine HCl).

These are the three types of Benadryl that are safe for dogs:

• Benadryl tablets (View on Amazon)
• Children’s Benadryl liquid (View on Amazon)
• Benadryl capsules (View on Amazon)

3. Benadryl Types to Avoid

• Time-release capsules (risk of overdose due to uneven absorption).
• Liquid Benadryl with alcohol or sodium (toxic to dogs).
• Benadryl containing xylitol (artificial sweetener toxic to dogs).
• Combination products (e.g., those with decongestants, acetaminophen, or other active ingredients).
• Topical Benadryl products (creams, sprays, or gels with additional ingredients unsafe for dogs).

4. Health Conditions Requiring Caution or Avoidance

Dogs taking certain medications (e.g., monoamine oxidase inhibitors, tricyclic antidepressants, some antifungals, potassium supplements, and specific diuretics) may be at increased risk for adverse effects or drug interactions. Benadryl should be used with caution or avoided in dogs with:

5. Special Considerations

• For small dogs, children’s Benadryl may allow for more accurate dosing.
• Liquid Benadryl is absorbed differently; consult your vet for proper dosing.
• Monitor your dog closely after administration, especially during the first hour, for any adverse reactions

Benadryl Toxicity In Dogs

Benadryl (diphenhydramine) is generally safe for dogs when used correctly.

In a study published in the Journal of the American Veterinary Medical Association, researchers reviewed 621 cases of diphenhydramine (Benadryl) exposure in dogs. They found that only 23.5% of the dogs developed any clinical symptoms—and when they did, the effects were typically mild, such as lethargy, agitation, tremors, or elevated heart rate. Serious outcomes were rare, with just three fatalities reported across all cases.^[5]

In another serious and rare case published in The Canadian Veterinary Journal, a 10-year-old poodle-cross was found deceased with evidence of diphenhydramine (Benadryl) overdose. The dog had pre-existing health conditions and was suspected to have also ingested ethanol alongside diphenhydramine—both factors that likely contributed to the fatal outcome.^[6]

Moreover, a third study found that Benadryl was well-tolerated by dogs when used within recommended dosing limits.

• At therapeutic levels, dogs experienced no organ damage, sedation, or cumulative toxicity.
• Mild stimulant effects, such as increased heart rate and respiration, were observed at low doses.
• Extremely high doses led to symptoms like sound sensitivity, nervous excitement, and—in rare cases—convulsions or respiratory depression.

Most dogs recovered quickly from non-lethal overdoses, and no signs of allergic reactions or long-term complications were observed over six months of use.^[7]

The findings from these three studies suggest Benadryl is generally safe for dogs. They also underscore the importance of proper dosing, as toxicity is dose-dependent, becomes more likely at higher levels of ingestion, and can be life-threatening.

Top reasons Benadryl can cause toxicity in dogs:

👉 Given the importance of dosage, we’ve created the most comprehensive Benadryl Dosage For Dogs Guide & Calculator to ensure you provide your dog with the right amount and avoid overdosing.

Are Dogs Allergic to Benadryl?

Yes, but it’s rare. Most dogs tolerate Benadryl (diphenhydramine) well, but allergic reactions can happen like any medication. Here are some reasons that could cause dogs to have an allergic reaction to Benadryl:

1. Diphenhydramine sensitivity – Rare, but some dogs react poorly to the drug itself.
2. Inactive ingredients – Fillers, dyes, or coatings in the pill might trigger allergies.
3. Overdose – Giving too much can mimic allergic reactions.

Drug Interactions

Benadryl can interact with various medications, potentially leading to adverse effects. Notable interactions include:

• Monoamine oxidase inhibitors (MAOIs) like amitraz or selegiline.
• Tricyclic antidepressants such as amitriptyline or clomipramine.
• Anti-nausea drugs like metoclopramide or cisapride.
• Anticholinergic drugs like atropine or glycopyrrolate.
• Potassium supplements and specific diuretics (e.g., hydrochlorothiazide).
• Sedatives and anesthetics (e.g., acepromazine, butorphanol).

MDR1 Gene Mutation & Benadryl Safety

Dogs with the MDR1 (ABCB1) mutation lack functional P-glycoprotein, a protein responsible for drug elimination and protecting the brain from toxins. Without this protein, drugs like Benadryl may cross the blood-brain barrier more easily, leading to heightened central nervous system effects, including severe sedation, tremors, seizures, or even coma. Herding breeds such as Collies, Australian Shepherds, and Shetland Sheepdogs are at higher risk for MDR1 sensitivity. Dogs with MDR1 mutations may require lower doses of Benadryl or alternative medications to avoid adverse reactions.

Veterinary consultation is essential to adjust dosages or select safer alternatives for MDR1-affected dogs. We highly recommend The EasyDNA MDR1 test to determine if your dog has this mutation. It allows your vet to tailor medication choices safely, including when Benadryl is considered.

Side Effects

The following symptoms may indicate a bad reaction to Benadryl.

• Drowsiness or sedation
• Dry mouth
• Urinary retention
• Vomiting or diarrhea
• Loss of appetite
• Agitation or hyperactivity
• Increased heart rate
• Confusion or disorientation

Serious side effects (contact your vet immediately):

• Seizures
• Difficulty breathing
• Collapse or fainting
• Loss of coordination or inability to walk properly

What to Do If A Dog Reacts Badly to Benadryl

Dogs showing worsening symptoms, such as blood in their vomit or stool, difficulty breathing, weakness, or collapse, should be taken to the veterinarian immediately.

1. Contact a veterinarian immediately: Even if your dog appears healthy, contact your veterinarian. In an emergency, if you cannot reach your veterinarian, immediately contact your local animal emergency clinic or a pet poison hotline. This includes services such as the ASPCA Animal Poison Control Center at 1-888-426-4435 or the Pet Poison Helpline at 1-855-764-7661. Alternatively, you can chat live with a registered online veterinary professional via our online vet chat or video chat support (24 hours a day, 7 days a week). You can also schedule an at-home veterinary appointment with The Vets, a mobile veterinary service that provides at-home vet care nationwide for just about everything.

2. Gather important information: When speaking to a vet, provide the quantity consumed (estimate if unsure), the time of ingestion, and the dog’s weight and breed (to assess potential risk).

3. Follow veterinary instructions: The vet may suggest monitoring at home or emergency treatment at the clinic.

• Keep your dog calm and prevent them from eating anything else.
• Be prepared to transport your dog to the vet quickly if advised.
• Bring any remaining Benadryl or packaging to help the vet assess the situation.

Ways to Feed Benadryl to Dogs

If your vet has approved Benadryl for your dog, here are some safe and easy ways to give it:

💊 Pill pocket or treat: Hide the Benadryl tablet inside a soft treat or a store-bought pill pocket. This is often the easiest and most stress-free method.

🥜 Peanut butter or canned food: Wrap the pill in a small spoonful of dog-safe peanut butter (make sure it doesn’t contain xylitol) or mix it with a bit of wet dog food.

🍽️ Crushed and mixed in: If your dog refuses pills, ask your vet if it’s okay to crush the tablet and mix it into their food. Some dogs may still notice the taste and avoid eating it.

🧴 Liquid form (vet-approved only): In some cases, a vet-approved liquid version of Benadryl can be used. Never use children’s liquid Benadryl unless your vet confirms it’s free of xylitol, alcohol, or other harmful ingredients.

🦴 Chewable tablets: Some Benadryl products or veterinary-prescribed versions come in flavored chewables that are easier for dogs.

🩺 With a pill dispenser: If your dog doesn’t take the pill any other way, a pill popper (pill gun) can be used to gently place it at the back of their throat, followed by water or a treat.

Can Puppies Use Benadryl?

Yes, puppies can take Benadryl, but only under the guidance of a veterinarian. While diphenhydramine—the active ingredient in Benadryl—is generally safe for adult dogs, puppies are more sensitive due to their developing bodies and smaller size. Getting an accurate dosage from your vet is crucial, as even a small amount of too much can lead to side effects like drowsiness, restlessness, or digestive issues. You should also avoid Benadryl products that contain additional ingredients like xylitol, alcohol, or decongestants, as these can be toxic to dogs—especially to young puppies. Liquid versions made for children should also be avoided unless your vet has confirmed they are safe and free from harmful additives. In short, while Benadryl can be used for puppies in certain cases, such as insect bites or mild allergic reactions, it should never be given without professional approval.

Can I Give Benadryl to My Dog For Anxiety?

Benadryl may have mild sedative effects, which can help calm some dogs during stressful events like thunderstorms or fireworks. However, it is not a reliable or recommended treatment for chronic anxiety. There are better options for anxiety management, including prescription medications and behavioral therapies. Always talk to your vet before using Benadryl for this purpose.

Alternatives

Here’s a list of alternatives to Benadryl that are just as safe and effective.

Frequently Asked Questions

The Bottom Line

While Benadryl can be a helpful tool for managing allergy-related symptoms like itching, swelling, and mild anxiety in dogs, it’s not a cure-all. It’s not effective for treating most types of coughing, and it shouldn’t be used as a substitute for proper veterinary care. Like any medication, Benadryl must be given at the right dose and for the right reason—and always with your vet’s approval. When used responsibly, Benadryl can offer safe, short-term relief and comfort for your dog. But when in doubt, the best course of action is to ask your veterinarian first.

Unexpected allergic reactions, emergency vet visits, and long-term medication can add up quickly. That’s why many pet parents choose the best pet insurance to help cover the cost of care and gain peace of mind. If you haven’t explored pet insurance yet, now might be a great time to consider protecting your dog’s health—and your wallet.

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Sources

Canine Bible uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process and product review methodology to learn more about how we fact-check, test products, and keep our content accurate, reliable, and trustworthy.

1. The anti-histamine properties of benadryl, beta-di-methylaminoethyl benzhydryl ether hydrochloride.
2. Modification of Anaphylaxis by Benadryl.
3. THE INFLUENCE OF DIPHENHYDRAMINE·HC1 (BENADRYL) ON APOMORPHINE-INDUCED EMESIS IN DOGS
4. Pharmacological Properties of Antihistamine Drugs, Benadryl, Pyribenzamine and Neoantergan
5. Diphenhydramine exposure in dogs: 621 cases (2008-2013)
6. Fatal diphenhydramine poisoning in a dog
7. A toxicologic study of two histamine antagonists of the benzhydryl alkamine ether group