Dog Zyrtec Dosage Calculator: How Much to Give & Charts

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

Whether your dog is dealing with seasonal allergies, itchy skin, or mild reactions to bug bites, Zyrtec (cetirizine) is a commonly used over-the-counter antihistamine that can offer fast relief when dosed correctly. But even safe meds can cause problems at the wrong dose—especially if you accidentally use products like Zyrtec-D (which contains a decongestant and is not safe for dogs). That’s why we created this Dog Zyrtec Dosage Calculator—to help you quickly determine how much Zyrtec to give based on your dog’s weight. In this guide, you’ll also find dosage charts, safety tips (including which dogs should avoid Zyrtec), and answers to frequently asked questions so you can treat your pup effectively and responsibly.

How Much Zyrtec Can I Give My Dog?

The standard Zyrtec dosage for dogs is 0.5 to 1 mg of cetirizine per kilogram of body weight (approximately 0.23 to 0.45 mg per pound), given once daily. Most veterinarians use this guideline when recommending over-the-counter dog antihistamines like Zyrtec for dogs dealing with allergies, itching, or skin irritations. Children’s Liquid Zyrtec (commonly 5 mg per 5 mL) is often recommended for dogs under 10 pounds, as it allows for more precise dosing than splitting adult tablets. However, if your dog dislikes liquid medication or you find measuring it inconvenient, standard 10 mg Zyrtec tablets are safe and effective for dogs of all sizes when dosed correctly.

Zyrtec product recommendations based on their type and strength:

Product Type	Common Strengths	Best For
Adult Zyrtec tablets	10 mg	Medium to large dogs (25+ lbs)
Children’s Liquid Zyrtec	5 mg per 5 mL (1 mg/mL)	Small dogs under 10 lbs
Smaller-dose tablets or scored tablets	5 mg	Small to medium dogs (10–20 lbs)

Zyrtec Table Dosage Chart for Dogs (By Weight)

Zyrtec Liquid Dosage Chart for Dogs

Dosing chart for dogs taking liquid Zyrtec.

Types of Zyrtec to Avoid Giving Your Dog  

⚠️ While cetirizine hydrochloride is the active ingredient in most Zyrtec products, not every “Zyrtec” item is safe for dogs. Some versions include decongestants (e.g., pseudoephedrine) or other additives that can be harmful.

🛑 If you’re outside the U.S., double-check the exact product name and ingredients. Only use products where cetirizine is the sole active ingredient and avoid any “D,” “Plus,” or “Duo” versions.

Zyrtec Forms to Avoid

When using Zyrtec (cetirizine) for dogs, avoid the following:

• Zyrtec-D / Zyrtec “Plus” / “Duo” combinations: Contain pseudoephedrine or other decongestants that are dangerous and potentially life-threatening to dogs.
• Liqui-gels / gel capsules: Hard to split for small-dog dosing and may deliver the full 10 mg when your dog needs less. Choose scored tablets or liquid instead.
• Adult liquid Zyrtec with problematic excipients: Some syrups (in certain markets) may contain alcohol or xylitol. Use Children’s Zyrtec 1 mg/mL and confirm the label is alcohol-free and xylitol-free.
• Extra-strength tablets (e.g., 20 mg): Can lead to accidental overdose, especially in small dogs. Standard 5 mg or 10 mg options are safer to dose accurately.
• Extended-release (ER/12-hr/24-hr) formulations: Dogs metabolize meds differently; ER coatings and combo products can result in uneven or unsafe absorption.

Bottom line: Use plain cetirizine only (no “D,” no decongestants), ideally Children’s liquid 1 mg/mL for small dogs or scored 5–10 mg tablets for accurate dosing. Always verify inactive ingredients and confirm dosing with your vet.

Safety Dosage Guidelines

Make sure to follow these important safety tips before giving Zyrtec (cetirizine) to your dog.

1. Use only plain Zyrtec with cetirizine as the active ingredient

• Avoid any products labeled Zyrtec-D, Zyrtec Plus, or anything containing decongestants such as pseudoephedrine — these can be toxic and potentially fatal to dogs.
• Steer clear of formulations that contain:
  • Pseudoephedrine or other decongestants (dangerous and potentially deadly)
  • Xylitol or alcohol in liquid form (both are highly toxic to dogs)
  • Other active antihistamines like loratadine or fexofenadine

2. Follow the proper dosage: Measure doses carefully, especially if using Children’s Liquid Zyrtec (1 mg/mL). Always start on the lower end of the dosage range (0.23 mg/lb) for small or sensitive breeds, and only increase under veterinary guidance.

3. Avoid if your dog has:

• Liver or kidney disease (these organs process cetirizine)
• Urinary retention or prostate issues
• Heart disease
• High blood pressure
• Seizure disorders
• Pregnancy or nursing period (unless prescribed by a vet)

4. Check with your veterinarian first if:

• Your dog is under 12 weeks old
• Your dog is pregnant or nursing
• Your dog is on other antihistamines, sedatives, or prescription medications

5. Watch for side effects: These include mild drowsiness, dry mouth, or digestive upset. Rare but serious symptoms include hyperactivity, rapid heartbeat, vomiting, diarrhea, or seizures.

What to Do If A Dog Reacts Badly to Zyrtec

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 seems fine, contact your veterinarian or an emergency pet poison hotline right away. This includes services like the ASPCA Animal Poison Control Center or Pet Poison Helpline at 1-855-764-7661. 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). 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 Zyrtec or packaging to help the vet assess the situation.

🧬 MDR1 Sensitivity and Zyrtec

Some dogs carry a genetic mutation in the MDR1 (Multi-Drug Resistance 1) gene, which affects how their body processes certain medications. This mutation is prevalent in herding breeds like Collies, Australian Shepherds, and Shelties.

While Zyrtec (diphenhydramine) is generally considered safe for most dogs, those with the MDR1 mutation may be more sensitive to its effects or to other medications that might be used alongside it—such as sedatives, anti-nausea drugs, or decontamination treatments in emergency scenarios. Knowing your dog’s MDR1 status is crucial if:

• You ever need to use Zyrtec alongside other medications.
• Your dog is receiving long-term allergy management.
• You want to avoid adverse drug reactions during emergency treatment.

The EasyDNA MDR1 test is a reliable way to determine if your dog has this mutation. It allows your vet to tailor medication choices safely, including when Zyrtec is considered.

Pro tip: If your dog is a herding breed or mixed with one, consider testing before using any medications, even over-the-counter ones like Zyrtec.

Calculate Zyrtec Dosage For Dogs Manually

Use these formulas to manually calculate your dog’s Zyrtec (cetirizine) dosage.

Tablet

Use this method if you’re giving your dog standard Zyrtec tablets (typically 5 mg or 10 mg per tablet):

1. Standard dose: 0.23–0.45 mg per pound of body weight (once daily)
2. Tablet strength: Most adult Zyrtec tablets contain 10 mg of cetirizine
3. Formula:
   Dog’s weight (in pounds) × 0.23–0.45 = total mg per day
   Then divide by tablet strength to find the number of tablets.

Example:
50 lb dog → 50 × 0.23–0.45 = 11.5–22.5 mg → 1 to 2 tablets of 10 mg each once daily

Liquid

Use this method if you’re using Children’s Liquid Zyrtec (commonly 1 mg per 1 mL):

1. Standard dose: 0.23–0.45 mg per pound of body weight (once daily)
2. Liquid concentration: 1 mg per 1 mL
3. Formula:
   Dog’s weight (in pounds) × 0.23–0.45 = total mg → equals mL to give

✏️ Example:
25 lb dog → 25 × 0.23–0.45 = 5.75–11.25 mg → give 5.75–11.25 mL once daily

Frequently Asked Questions

The Bottom Line & Alternatives

Zyrtec can be an effective, safe, and convenient way to relieve your dog’s allergy symptoms — from itchy skin and sneezing to watery eyes — when used correctly and at the proper dose. As with any over-the-counter medication, accuracy and caution are key. Always use plain Zyrtec (cetirizine) without added decongestants like pseudoephedrine, and start with the lowest effective dose for your dog’s size and condition. Before giving Zyrtec regularly or alongside other medications, talk to your veterinarian to confirm it’s the right fit for your dog’s health needs. With proper dosing and guidance, Zyrtec can help your pup find lasting relief from seasonal or environmental allergies — and get back to feeling their best.

If Zyrtec isn’t providing enough relief or you’re looking for gentler, longer-term alternatives, you might want to explore CBD oil for dogs—which some pet owners use to naturally manage both allergies and anxiety. You can also check out our guide to the best allergy medicine for dogs for prescription and non-prescription options beyond Zyrtec. Concerned your dog’s symptoms may be caused by an underlying allergy? Getting a dog allergy test can help identify food or environmental triggers so you can treat the root cause—not just the symptoms. For dogs dealing with stress, travel anxiety, or loud noises like fireworks, Zyrtec may not always be the ideal long-term solution. In that case, explore our calming strategies and products in how to calm dogs with anxiety.

With the charts, calculators, and tips in this guide, you now have everything you need to safely and confidently dose Zyrtec—and understand when it might be time to try something more targeted.

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Sources

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