Interceptor Plus is a monthly chewable tablet that protects dogs against five types of intestinal parasites and prevents heartworm disease. Made by Elanco, it contains two active ingredients: milbemycin oxime, which targets heartworms, roundworms, hookworms, and whipworms, and praziquantel, which handles tapeworms. It’s FDA-approved for dogs and puppies weighing at least two pounds and at least six weeks old.
What Interceptor Plus Protects Against
Interceptor Plus covers a broader range of parasites than most monthly preventives. It prevents heartworm disease, which is transmitted by mosquitoes and can be fatal if left untreated. It also treats and controls five categories of intestinal worms: roundworms, hookworms, whipworms, and four species of tapeworm, including the type dogs pick up from swallowing fleas.
That tapeworm coverage is the main reason the “Plus” exists. The original Interceptor (milbemycin oxime alone) already handled heartworms, roundworms, hookworms, and whipworms. Adding praziquantel gave the Plus version the ability to kill tapeworms, making it one of the few monthly preventives that covers all five major worm types in a single tablet.
How It’s Given
Interceptor Plus comes as a flavored chewable tablet given once a month, year-round in most cases. The tablet size is based on your dog’s weight, with formulations covering dogs from 2 to 10 pounds, 11 to 25 pounds, 26 to 50 pounds, and 51 to 100 pounds. Dogs over 100 pounds get a combination of tablets to reach the correct dose.
Before your dog starts Interceptor Plus for the first time, or if you’ve missed doses and are restarting, your vet will need to run a heartworm test. Giving a heartworm preventive to a dog that’s already infected can cause serious complications, so that blood test is a necessary first step.
Common Side Effects
Most dogs tolerate Interceptor Plus well. The side effects that do show up tend to be mild and digestive in nature: vomiting, diarrhea, decreased appetite, or lethargy. These typically resolve on their own within a day or two. Serious reactions are uncommon at the standard preventive dose.
Safety Concerns for Certain Breeds
One of Interceptor Plus’s active ingredients, milbemycin oxime, deserves extra attention if you own a herding breed. Dogs with a genetic mutation called MDR1 (also known as the ABCB1 mutation) have trouble keeping certain drugs out of their nervous system. At the standard heartworm preventive dose, milbemycin oxime is considered safe for these dogs. The risk comes from higher-than-labeled doses or from combining the medication with certain other drugs that can amplify its effects in the brain.
Breeds most commonly carrying the MDR1 mutation include Collies, Shetland Sheepdogs, Australian Shepherds, Old English Sheepdogs, and Long-Haired Whippets, though it can appear in other herding breeds too. If your dog is one of these breeds and you haven’t had them genetically tested, it’s worth doing before adding any new medications on top of their monthly preventive. Signs of a toxic reaction in an MDR1 dog include dilated pupils, drooling, loss of coordination, seizures, and in severe cases, coma.
Some medications that can interact dangerously with milbemycin oxime in MDR1 dogs include certain antifungal drugs, the immunosuppressant cyclosporine, and the antibiotic erythromycin. If your dog takes any of these, make sure your vet knows they’re also on Interceptor Plus.
Who Interceptor Plus Is Not For
Interceptor Plus is a dog-only product. It should not be given to puppies under six weeks of age or dogs weighing less than two pounds. There is no cat formulation. If you need parasite prevention for a cat, you’ll need a different product entirely.
How It Compares to Other Preventives
The monthly heartworm preventive market has several popular options, and the differences mostly come down to which parasites each product covers beyond heartworm. Many competitors protect against heartworms, roundworms, and hookworms but skip whipworms or tapeworms. Interceptor Plus stands out by covering all five worm types in one chewable. The tradeoff is that it does not protect against fleas or ticks, so dogs on Interceptor Plus typically need a separate flea and tick product.
If tapeworms aren’t a concern for your dog and you’d prefer a single product that also handles fleas or ticks, a combination preventive might make more sense. But if your dog has had tapeworms before, lives in an area with heavy flea exposure, or you simply want the broadest deworming coverage available in one monthly dose, Interceptor Plus fills that role effectively.