Can Heartworm Medicine Make Your Dog Sick? The Truth About Prevention Risks

Let’s face it – as dog parents, we’re constantly worried about keeping our furry friends safe from nasty parasites like heartworms. But what if the very medicine meant to protect them could actually make them sick? It’s a scary thought, but one we need to address.

After researching this topic extensively, I’ve discovered some concerning information about heartworm medications that your vet might not be telling you. Let’s dive into the real risks and side effects these drugs can have on your beloved pup.

The Truth About “Preventative” Heartworm Medication

First things first – that “preventative” label on heartworm medicine? It’s a bit misleading Here’s why

• These medications don’t actually prevent heartworms from entering your dog’s body
• Instead, they kill heartworm larvae that may already be present after a mosquito bite
• They’re actually treatment drugs, not preventative drugs
• They treat a condition your dog may not even have!

As the folks at Dogs Naturally Magazine point out, heartworm drugs are essentially pesticides that work by paralyzing the worm’s nervous system. That doesn’t sound so great for your dog’s own nervous system, does it?

Common Side Effects of Heartworm Medications

Yes, heartworm medicine absolutely can make your dog sick. The FDA has received thousands of Adverse Drug Experience (ADE) reports for popular heartworm medications. Here are some of the most common side effects reported:

Digestive Issues

• Vomiting (sometimes with blood)
• Diarrhea (sometimes with blood)
• Loss of appetite
• Hypersalivation

Neurological Problems

• Seizures
• Ataxia (loss of coordination)
• Trembling
• Weakness
• Depression/lethargy

Skin Reactions

• Itching
• Hair loss (especially at application sites for topical treatments)
• Urticaria (hives)

Severe Reactions

• Anaphylaxis
• Collapse
• In some extreme cases, death

And get this – many veterinarians don’t even report these side effects to the FDA, either because they don’t recognize them as being related to the heartworm medication or because they’re too busy to file a report. So these adverse reactions are likely much more common than the official numbers suggest!

Major Heartworm Medications and Their Specific Risks

Let’s break down some of the most popular heartworm drugs and their reported side effects

Heartgard Plus, Iverhart Plus, and TriHeart Plus

These medications all contain ivermectin and pyrantel pamoate. According to ADE reports, top issues include:

• Ineffectiveness against parasites (yes, sometimes they don’t even work!)
• Vomiting
• Diarrhea
• Depression/lethargy
• Seizures
• In some cases, death

Sentinel and Interceptor

These meds contain milbemycin oxime (Sentinel also includes lufenuron). Common problems reported:

• Ineffectiveness against parasites
• Vomiting
• Depression/lethargy
• Diarrhea
• Itching
• Trembling
• Seizures

Trifexis

This controversial drug combines milbemycin oxime with spinosad. It’s gotten so much negative attention that there’s even a Facebook page called “Does Trifexis Kill Dogs?” Reported issues include:

• Vomiting
• Depression/lethargy
• Lack of effectiveness against fleas
• Loss of appetite
• Seizures
• Trembling

Revolution and Advantage Multi

These topical options aren’t necessarily safer. Revolution (selamectin) reports include:

• Ineffectiveness
• Vomiting
• Depression/lethargy
• Skin issues

Advantage Multi (imidacloprid and moxidectin) has been linked to

• Depression/lethargy
• Vomiting
• Loss of appetite
• Skin problems
• Behavioral changes

ProHeart 6 and ProHeart 12

These injectable medications deserve special attention. ProHeart 6 was actually recalled in 2004 after over 5,500 adverse events were reported, including approximately 500 deaths! It’s back on the market now, along with a longer-lasting version, but the manufacturer’s own prescribing information lists a shocking array of potential side effects, including:

• Immune system reactions (anaphylaxis, shock)
• Gastrointestinal problems
• Neurological issues (seizures, trembling)
• Liver problems
• And much more

The worst part? Since these are injectable medications that last 6-12 months, if your dog has a bad reaction, you can’t just stop giving the medicine. It’s already in their system for the duration.

Why the Risks May Outweigh the Benefits

So why do vets still recommend these medications? Well, heartworm disease is certainly serious and can be fatal if left untreated. But there are some important facts to consider:

1. The medications don’t always work – ineffectiveness is one of the most commonly reported issues
2. Your dog may be exposed to toxic chemicals monthly for a disease they might never get
3. Long-term use puts strain on your dog’s liver and kidneys as they work to remove these toxins
4. The weakened immune system after taking these pills may make your dog more susceptible to other diseases

Natural Alternatives to Consider

The good news is that you don’t have to choose between heartworm disease and potentially harmful medications. There are natural approaches to consider:

Strengthen Your Dog’s Immune System

• Feed a nutrient-rich diet
• Ensure regular exercise
• Reduce exposure to environmental toxins

Prevent Mosquito Bites

• Use natural mosquito repellents (diluted essential oils like lemongrass or eucalyptus)
• Keep your yard free of standing water
• Limit outdoor time during peak mosquito hours

Consider Herbal Options

• Some holistic vets recommend herbs like black walnut, wormwood, and small amounts of garlic

Test More Frequently

• Rather than giving preventative medicine year-round, consider more frequent testing (every 3-6 months)
• This allows for early detection while avoiding unnecessary medication

Special Considerations for Sensitive Dogs

Some dogs are more prone to medication sensitivities than others. According to VetInfo, certain breeds like shelties and dobermans seem to show increased sensitivity to heartworm medications. If your dog has:

• A history of seizures
• Previous reactions to medications
• Liver or kidney issues
• Breed-specific sensitivities

…you should definitely consult with your vet before giving any heartworm medications, and perhaps look into alternative approaches.

My Personal Take

I’ll be honest – I’ve struggled with this decision for my own dogs. After seeing one of my pups have a scary reaction to a heartworm pill (vomiting and lethargy that lasted for days), I started researching alternatives.

What I’ve learned is that there’s no one-size-fits-all approach. The right choice depends on:

• Where you live (heartworm risk varies by region)
• Your dog’s individual health status
• Your comfort level with different approaches

For me, I’ve moved to a more natural approach with more frequent testing, and I feel good about that decision. But whatever you choose, make sure it’s an informed choice!

Final Thoughts

Yes, heartworm medicine can definitely make your dog sick. While heartworm disease is serious, the medications used to prevent it come with their own set of risks that shouldn’t be ignored.

The most important thing is to be aware of these potential side effects so you can make an informed decision and keep a close eye on your dog after administering any medication. And remember – there are alternatives that might be worth exploring with your holistic vet.

Your dog depends on you to make the best healthcare decisions for them. By educating yourself about both the benefits AND risks of heartworm medications, you’re being the advocate your furry friend deserves.

Have you experienced side effects from heartworm medications with your dog? I’d love to hear your experiences in the comments below!

Yes, heartworm medicine can make some dogs sick, though side effects are usually mild and transient, such as vomiting, diarrhea, and lethargy. More severe reactions, like seizures or paralysis, are rare and may indicate a sensitivity to certain medications (especially ivermectin in Collies), a high dosage, or the presence of a severe heartworm infestation.

Heartworm treatment can cause side effects like injection site soreness, fever, lethargy, coughing, appetite loss, vomiting, and difficulty breathing, which often stem from the body’s reaction to the dying worms. Serious, but less common, complications include pulmonary emboli, anaphylaxis, abscesses at the injection site, and even sudden death.

Yes, heartworms can cause diarrhea in dogs and cats, though it is not one of their most common symptoms. Diarrhea can be a sign of digestive upset due to the immune response to the heartworm infection, or in some cases, can be a sign of abdominal issues caused by the parasites themselves.