Dogster is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Can You Buy Heartworm Medicine Over the Counter for Dogs? Vet-Reviewed Facts & FAQ

Written by: Nicole Cosgrove

Last Updated on April 18, 2024 by Dogster Team

person feeding poodle pet dog with preventive heart worms chewable

Can You Buy Heartworm Medicine Over the Counter for Dogs? Vet-Reviewed Facts & FAQ


Dr. Chyrle Bonk Photo


Dr. Chyrle Bonk

DVM (Veterinarian)

The information is current and up-to-date in accordance with the latest veterinarian research.

Learn more »

As important as it is for regulators to control prescriptions, many owners find it odd that heartworm medicine isn’t available over the counter. After all, heartworm preventives aren’t like medications provided on a case-by-case basis. Since every dog needs them, why wouldn’t they be as easy to obtain as possible?

It may seem needlessly complicated, but regulators have several reasons for making these preventives a prescription. Let’s discuss how we obtain heartworm medicine and why sticking to the process is the surest and safest way to protect our dogs.

dogster face divider

Can You Buy Heartworm Medicine Over the Counter For Dogs?

Heartworm medicine is available by prescription only. Sites like Chewy or PetMeds offer 30-day topical products or chewable tablets, but they still require a prescription to place an order. Alternatively, vets can provide an injection that lasts six or 12 months.

Nice dog before injection at vet office

What Are Heartworms in Dogs?

Heartworm prevention is a serious matter for vets, particularly regarding dogs. Canines are the definitive host for heartworms. Heartworms are passed when a mosquito ingests microfilaria from an infected dog. Once inside the mosquito, the microfilariae become infective larvae and can be transferred to another dog with the mosquito bites them. The larvae can take up to 6 months to mature into adults, so dogs won’t typically show physical issues for quite a while.

Most dogs will only experience mild signs in the early stages of heartworm disease. The first sign to show up is often a persistent cough. The longer the infection goes without the treatment, the worse the signs can get.

Chronic and severe infections can lead to clinical signs including:
  • Exercise intolerance
  • Rapid or labored breathing
  • Decreased appetite and weight loss
  • Fainting

In worst-case scenarios, heartworms can cause heart failure and caval syndrome which is when large numbers of worms block the blood supply to parts of the heart. The prognosis for dogs with caval syndrome is often death.

Dogster_Website dividers_v1_Jan 18 2024-01-TEST

Why Is Heartworm Medicine Prescription Only?

The effects of heartworm infections can be dire, and the treatment is arduous and stressful. An infected dog needs several weeks of medicine to kill the adult and larval heartworms, all while staying relaxed and relatively sedentary. Vigorous activity can result in blood clots, stroke, or even death.

Due to the risks inherent in dogs having heartworms and the treatments to remove them, we can’t overstate the importance of proper prevention. Heartworm medicine is prescription-only to ensure it’s effective, safe, and properly administered.

labrador retriever dog lying on the floor looking sad or sick
Image Credit: Jaromir Chalabala, Shutterstock

Specific Dosing

Dogs come in all sizes and body types. As with most medications, providing the correct heartworm medicine depends on the dog’s weight and specific tolerances. Giving the wrong product or amount can expose dogs to infection or adverse reactions.

For example, some Collies and similar dog breeds have an MDR1 gene mutation that makes them uniquely sensitive to the medication ivermectin. Although toxicity is unlikely at the low doses in 30-day tablets, products like Heartgard are less viable for these dogs because they’re more likely to cause issues like lethargy, ataxia, tremors, and possibly death.

Since heartworm medicines aren’t OTC, vets control the process to provide suitable medicine in the proper dosage.

Well-Timed Administration

Letting time lapse between 30-day, bi-annual, or annual heartworm medications creates a window of opportunity for parasites to infect your pet. Many 30-day treatments have a minor buffer past their 30-day range, but it’s easy for owners to skip the doses entirely.

By making heartworm medicines available only through your dog’s doctor, timing the administration can involve a reminder from your vet. Owners will be much less likely to miss a dose when they have that support, ensuring their dogs are always protected.

dogster face divider

The Importance of Heartworm Testing

Heartworm prevention coincides with heartworm testing, which is an annual requirement. Veterinarians perform blood tests to look for heartworm antigens or microfilariae in the dog’s system. Once they confirm a dog is parasite-free, they can prescribe another 12 months of treatment.

Testing may seem redundant if you’ve given your dog heartworm medicine responsibly. If there have been no lapses between doses, why would you need to check for worms before prescribing more? Vets insist on it to verify the medicine’s effectiveness and account for medication-resistant heartworms.

blood samples of a dog for lab testing
Image Credit: hedgehog94, Shutterstock

Medication-Resistant Heartworms

Heartworms resistant to macrocyclic lactones (MLs), the active ingredients in heartworm preventives, are an isolated but growing issue. Since 2005, experts have recognized the loss of efficacy of every ML against certain strains, prompting the FDA to look for new solutions.

Resistant parasites are a particular concern in Southeast regions like the Mississippi Delta.

Even if dogs receive timely treatments, a slight chance of infection remains that only blood tests will reveal. Without screening, dogs could harbor resistant strains for years. Alongside the harm to their body, this could allow the resistant parasites to attack other dogs in the area. Annual exams let practitioners track, study, and react to heartworm cases, helping to prevent their spread.

Preventing Adverse Effects

Without testing, you could give your dog prevention medicine while they secretly have an infection. Not only would this be a waste of time and money and risk the spread of heartworms, but it could also cause adverse reactions that can be harmful to your dog’s health.

When an infected dog takes a standard heartworm preventive, the medicine may cause young heartworm larvae to die rapidly which can trigger a shock-like reaction. Although this is rare, a heartworm test is a simple way to prevent a potentially fatal situation.

Dogster_Website dividers_v1_Jan 18 2024-03

Which Home Remedies Can I Give for Heartworms?

Although numerous brands sell herbal heartworm medicines that don’t need a prescription, no studies have evaluated their effectiveness. Many manufacturers acknowledge the products shouldn’t replace preventatives. Natural remedies may help boost immunity and manage the side effects of treatments, but they aren’t proven to prevent or treat heartworms in dogs.

However, natural remedies can protect dogs when used as mosquito repellents. Though they don’t remove the need for heartworm preventatives, natural mosquito repellents offer another way to reduce the risk of transmission.

Products like Vet’s Best mosquito repellent and natural herbs may help your dog stay bite-free. Since many essential oils, herbs, and human products (like DEET) can be toxic to dogs, discuss safe at-home solutions with your vet before using them on your dog.

Anti mosquitoe and anti-insect for active dog outdoors
Image Credit: Aleksey Boyko, Shutterstock

Is There Any Way to Get Heartworm Medicine for Dogs Over the Counter?

A common way some owners try to sidestep getting a heartworm prescription is to use ivermectin intended for larger animals. Ivermectin for horses is available OTC at feed stores. Many people think scaling down the dose can prevent heartworms at a fraction of the cost of medicine for dogs.

However, heartworm preventives for livestock are exceptionally potent and highly dangerous to dogs. Dogs can suffer ivermectin poisoning simply by getting into manure from animals that have been treated with ivermectin. When administering a paste, scaling down to a safe yet effective amount is extremely challenging.

It’s easy to give too much and cause a veterinary emergency, and it’s almost impossible to tell whether you administered enough to make it effective. The only person who can advise on using these non-canine medicines is your vet.

It doesn’t make sense for people who can get safe and effective heartworm medicine for dogs just as easily. Play it safe, and stick to testing and prescriptions through your vet.

dogster face divider

Final Thoughts

With the risks surrounding heartworm disease and its treatment, owners owe it to their dogs to take the issue seriously. It only takes one missed test or the wrong dose to set a pet up for potentially lifelong complications. Though avenues exist for owners to try to sidestep prescriptions and get OTC heartworm medicines, working with a vet is the only responsible route to prevent a potentially fatal infection.

Featured Image Credit: ThamKC, Shutterstock

Get Dogster in your inbox!

Stay informed! Get tips and exclusive deals.
Dogster Editors Choice Badge
Shopping Cart


© Pangolia Pte. Ltd. All rights reserved.