I am concerned about the safety of heartworm medication. Should I still give it to my dog even though he’s tested for heartworm every year?

Hi Sandra

Thanks for your question.

The first thing I will address is the heartworm risk issue that you have. From what you’re telling me, your dog did not have protection from contracting the heartworm parasite last year for a large percentage of the season. What this means is that your dog could have contracted heartworm and this increases the need to have a heartworm test performed at the start of this season. It takes about 5 1/2 months for the parasite to develop to a point where the test will yield a positive result. So now is the time to perform the test.

I feel the need to also mention the risk of heartworm in general. It is known to be quite low if you live in the area that I do, which is South Central Ontario. The risk of contracting heartworm is approximately 1 in 1000 to 1 in 10,000 so you’ll likely agree that the risk is very, very small. You’ll want to confirm this with your veterinarian and get their impression of the risk in your particular area if you don’t share the same one that I do. Understanding this risk is really important as we answer your next question regarding the usefulness and safety of the medication.

If your dog has received this treatment in the past, which your question suggests he has, then you likely know that he hasn’t had any reactions to it. But I believe your question is more about the cumulative effect of these medications over time. The fact that you feed a raw food makes me think that you’re more of a pet owner who opts for a natural approach to medical and dietary health for your dog. Quite frankly and honestly, I don’t have a really good answer for the cumulative effect of these drugs over many years. I have personally seen dogs take these drugs every year for their lives and live out very long happy lives. Research studies show that these drugs are safe when given unless your dog has a particular allergy or sensitivity which would show up when you administer them. My best advice is to call the companies that produce these medications and speak to them about the studies and pose the question to them. You’ll want to ask for the results of long-term studies to confirm in your mind that they are safe. At the same time, any drug that we take has side effects. It only takes a minute to look at the exhaustive list of side effects of something simple like aspirin to understand this and yet billions of people have taken aspirin every day since it was first developed. Again, that doesn’t mean it’s safe because just like my wife, someone can have an allergy to aspirin.

Ultimately, the only person who can truly answer your question is yourself. You have to collect this objective information, determine if it’s valid to you and then make a decision on whether to administer these medications based on the risk versus benefit of them. The risk of contracting heartworm, as we discussed, is very low. The problem is that if heartworm is contracted it is a terrible disease. The medication will reduce or totally eliminate that risk as it is known to be extremely effective. I would also recommend that you reach out to veterinarians that have received extra training in naturopathic medicine or alternative medicine where they may have access to natural products meant to reduce the chance of contracting heartworm. I’m not going to advise you on this because I don’t have that training and more importantly, I have not had personal experience using those kinds of medical products to treat this disease. I would encourage you to look locally for a veterinarian with this type of training because it sounds to me like this is the direction you would always consider going forward with. I think developing a relationship with a veterinarian with that discipline of training may be a better fit for the philosophy of care you would like to see your dog receive.

There are some pet owners who don’t give any heartworm medication but they still perform the heartworm test to make sure that they are monitoring whether their dog has contracted it or not. So I still recommend that you perform the test because it has no side effects other than a needle poke and it will yield very valuable information for you and your dog.

I hope this helps. Good luck!

Dr. Greenway