Heartworm Pills: Seriously Sick


Last Updated on October 23, 2023 by Will Falconer, DVM

Heartworm Pills: Seriously Sick

“Angel is very sick and has been in intensive care at a vet clinic here in Asheville.”

This landed in my inbox April 9. It was from Jan, a past client I hadn’t heard from in about a year and a half. When I dug back into Angel’s case with Jan’s help, something surfaced: she was bouncing in and out of horrible diarrhea and vomiting, even landing her in the ER.

The timing was such that her sickness returned several days to a week after she’d gotten her monthly heartworm pills.

Sentinel, if you’re keeping score on brands. I think they are likely to all be similar in risk, though.

Intensive Care. Oh oh.

Luckily, Jan and I were able to make a time together that same day, and I learned more about Angel’s serious disease, now presumed “inflammatory bowel disease” or IBD.

She was one sick dog. So sick, she’d been in intensive care just six days before we talked. The symptoms that landed her there?

“She had diarrhea that was pure blood. I thought she was going to die.”

Angel would start a typical round of this illness with loud, (wake-up!) gurgling in her intestines, in the middle of the night. This often progressed to vomiting, and then, 30 to 60 minutes later, pouring diarrhea.

Poor thing.

Released from the E.R. just five days earlier, with a finding of pancreatitis this time, Jan was calling now because Angel was sick again. She’d had one good day and bounced back into spit ups, then diarrhea that was just liquid. Of course, she was on every anti- drug that might apply:

  • Anti-nausea

  • Anti-diarrhea, anti-inflammatory, etc.

  • And, Dr. WhiteCoat’s favorite: Antibiotics (really? this was all caused by a bacteria, then?)

And, of course, she was put on i.v. fluids and allowed no food. She’s just a wee thing, without much reserves.

First Take Away: HW Pills are Immune Wreckers

So, in this disease of inflammatory bowel, or IBD, what’s going on inside, exactly? The definitive diagnosis comes from a biopsy, sampling a tiny piece of the lining of the lower intestinal wall, which is examined under a microscope.

And the culprit is: Angel’s Immune System!

Wait. You mean that finely tuned, amazingly intelligent system that was designed to protect her against all manner of threats, from nasty viruses to cancer?

Yep. That system. Now attacking her intestines.

But that’s crazy!

Agreed. And this is one more example of the damage that heartworm pills can wreak. I wrote of other, more deadly versions here.

Homeopathy: DIY?

Somehow, Jan had discovered a remedy that was “working” quite well for several of the past episodes of this GI illness: nux vomica, aka “the hangover remedy.” Angel got ill, Jan would give her a few doses of the nux, and she’d have a few good weeks.

Before taking her next heartworm pill. Then it would start all over again.

dog getting medicineSpin the drug-roulette wheel now. Whee!

Now for those who’ve learned a few remedies, it makes perfect sense that nux would help Angel. It’s a remedy for sick digestive systems. Liver problems. And, …wait for it…

…states of intoxication.

So, yet another point in favor of this being a drug-caused illness. Angel was given her monthly heartworm drug, became sick from the drug in a serious way, and she was remedied by a substance known to help with detoxification.

Don’t Try This at Home, Kids!

But, while that sounds useful on the surface, another take home point is this:

Angel had chronic disease. And repeated dosing of nux vomica was doing nothing to cure that chronic disease. It palliated it nicely. Which means, it made the symptoms go away without correcting the deeper disorder, (which we’d actually seen signs of from her early days).

And, without moving her in a curative direction, nux was allowing her chronic disease to grow.

“This last time, (the nux vomica) didn’t work. That’s why we ended up in the E.R.”

There’s a very valuable lesson here: unless you’re trained to manage chronic disease, it’s best to save your use of remedies for truly acute troubles only.

Acute, as in sudden injury (try arnica). Garbage gut (try arsenicum album). Bee sting (apis, STAT).

Chronic diseases reoccur, get slowly worse over time, and need professional help to cure.

So, I’ve got work to do now. We’ve got to not just get Angel out of this horrible dilemma of gut distress and diarrhea, but we’ve got to cure her, so she doesn’t keep repeating her trips to the E.R. It’ll take time, but we’ll get there, quite likely.

Angel: You are Not Alone

I recently rewrote my drug free heartworm prevention book, and called on my colleague Jean Dodds, DVM, famous for her work in blood diseases and immunology.

Years ago, Dr. Dodds presented at the AHVMA about the growing number of dogs getting seriously ill after heartworm pills and vaccinations. She kindly sent me her paper focused entirely on the former, published years ago in a vet journal.

The data were downright scary.

Dr. Dodds catalogued disease coming after the heartworm monthly pills (Ivermectin or Milbemycin) that ranged from

  • lethargy

  • staggering

  • vomiting and diarrhea

  • unable to rise

all the way to

  • sudden death “2 days after dose”

  • bone marrow failure

  • seizures

  • severe ITP (immune mediated thrombocytopenia, not able to clot blood)

  • liver failure

  • IMHA and death (immune mediated hemolytic anemia, dying from immune attack on the dog’s own red blood cells)

Hey Teacher, What’d You Learn?

You know how it’s often said that the teacher learns more than the students? Rewriting my drug free heartworm book (and making it into an audiobook and course!) has clearly been an eye opener for me. I had relegated heartworm preventatives to a mildly intoxicating “hit” on those who received them monthly. They were not a good thing, but the animal could recover, they’d get over it.

It’s crystal clear to me now that these drugs pack a much more insidious wallop than just toxins. They are immune disrupters. Serious risks to your animal’s health and very existence.

Think about your own experiences of monthly heartworm drugs. We’d all love to read any insights your animals spoke to you about around the first of every month. Angel’s is not an exceptional case. Not by a long shot.

I believe Vital Animals can change the world

One shiny, well-balanced individual at a time.


It all starts with you, the wise animal caregiver, and the health choices you make for the animals in your care.

And that's why this site is here. Care to join us? We're a Vital Animal Pack.

I'm in!