Written By Mel Lee-Smith
Published: 09/14/2020Updated: 08/30/2021
Interceptor for Dogs | Wag!

Interceptor is an antiparasitic medication and heartworm preventative available by prescription for dogs and cats. The active ingredient in Interceptor is milbemycin oxime, which kills heartworm larvae and mature hookworms, roundworms, and whipworms in canine body tissue. 

Interceptor belongs to a group of antiparasitics called anthelmintics, which selectively target the neurological function of invertebrate nematodes without harming the infected animal. 


Interceptor for dogs comes in 4 dosages:

  • ¬†2.3 mg for dogs under 10 lbs

  • ¬†5.75 mg for dogs between 11 and 26 lbs

  • 11.5 mg for dogs between 26 and 50 lbs

  • 23 mg for dogs between 51 and 100 lbs

Interceptor can be given for dogs as young as 6 weeks old, as long as they weigh at least 2 lbs. Most vets recommend pet parents start this medication as soon as its safely possible. Typically Interceptor for dogs is given as a single tablet once every 30 days. Try to give this medication at the same time every month. Some people find it helpful to schedule a recurring reminder on their phone to let them know when their pets' meds are due.


The cost of Interceptor for dogs varies depending on the dosage strength. Expect to pay anywhere between $35 and $55 for a box of 6 treatments.


A double-blind study of 40 dogs infected with heartworms found the active ingredient in Interceptor to be 52% effective (compared to the controls) at killing heartworm larvae compared to the 100% efficacy of imidacloprid/moxidectin. This study also determined the active ingredient of the Interceptor was nearly twice as deadly to heartworms as ivermectin, pyrantel pamoate, and selamectin. 

A separate study on the antiparasitic properties of milbemycin oxime and praziquantel (the main ingredients in Interceptor Plus) found the combination destroyed 100% of the nonvertebral parasites in the canine study group. 

Side effects

Side effects from Interceptor are rare, but they do happen. Here are the most common:

  • Mood changes

  • Poor appetite

  • Excessive salivation

  • Muscle weakness

  • Seizures

  • Loose stools

  • Tremors

  • Disorientation

  • Depression

  • Lethargy


Some types of intestinal worms like hookworms and roundworms are transferable from animals to humans. Wash your hands with soap and water for at least 30 seconds after petting, feeding, or picking up your dog's waste.

If your dog is switching from another heartworm preventative medication, wait until the next dose to begin Interceptor. Do not start Interceptor if your dog hasn't been tested for heartworms or is heartworm-positive. Giving Interceptor to a dog with heartworms can cause serious injury and even death. If your pet misses more than 6 consecutive doses of Interceptor for dogs, they should be tested upon resuming treatment. 

Since milbemycin oxime, the active ingredient in Interceptor, binds to GABA receptors, it can sometimes lead to depression in canines. Talk to your vet if your dog exhibits changes in eating and sleeping patterns, abnormal behavior, or becomes less active. 

Drug interactions

Interceptor has been used safely in combination with a wide variety of medications, and scientists have found very few contraindications with this drug. Interceptor should not be used in conjunction with other heartworm preventatives or oral antiparasitics since these can cause overdose toxicity and death. 

Avoid giving Interceptor with any of the following:

  • Trifexis

  • Heartgard¬†

  • Tri-heart plus

  • Revolution

  • Sentinel¬†

  • Sentinel Plus¬†

  • Sentinel Spectrum

  • Advantage Multi

  • Interceptor Plus

  • Iverheart Max

  • Selarid (Selamectin)

  • Coraxis

  • Centraguard

  • MilbeGuard

  • Simparica TRIO

  • Ivermectin

Allergic reactions and sensitivity

Ask your vet before giving Interceptor for dogs that are sensitive to ivermectin, milbemycin, or similar antiparasitics. Signs of a drug reaction to heartworm preventatives include:

  • Excessive scratching

  • Swelling of the muzzle, tongue, or throat¬†

  • Whining

  • Labored breathing

  • Difficulty breathing¬†

  • Hives

  • Unsteady gait

Frequently asked questions

I just found out my dog is pregnant. Should I stop giving them Interceptor? 

No. Interceptor is perfectly safe for pregnant and nursing dogs.

Does my dog need Interceptor year-round?

Most vets recommend dogs take a heartworm preventative monthly, particularly in hot climates where mosquitos breed year-round. 

How do dogs get heartworms?

Dogs contract heartworms by being bitten by a mosquito infected with the parasite. 

How are hookworms transmitted?

Both humans and canines can contract hookworms by walking in contaminated dirt. Dogs may also pick up hookworms by ingesting food or fecal matter containing hookworm eggs or larvae. 

Does Interceptor kill whipworms and roundworms in dogs with an active parasitic infection?

Yes! Interceptor rids canines of whipworms and roundworms and prevents them from contracting these parasites in the future. 

Does Interceptor treat whipworms and tapeworms? 

Interceptor prevents three types of parasites: hookworms, roundworms, and heartworms. Interceptor Plus prevents those same parasites but also offers protection against whipworms and tapeworms. 

Is Interceptor flavored?

Yes! Interceptor is a chewable beef-flavored tablet. 

Will Interceptor treat heartworms in a heartworm positive dog?

No. Melarsomine is the only FDA-approved treatment for heartworms. Never give Interceptor to a heartworm positive dog, severe, and even deadly side effects can arise. 

Does Interceptor prevent fleas and ticks? 

No, your dog will still need preventative meds for fleas and ticks while on Interceptor. 

What are the symptoms of an Interceptor overdose?

  • Loss of eyesight

  • Uncoordinated movements

  • Uncontrolled drooling

  • Shakiness

  • Loss of consciousness

Can my dog still get heartworms on Interceptor for dogs?

Unfortunately, yes. No heartworm preventative is 100% effective all the time. Dispensing errors, vomiting after taking their meds, improper dosage, and improper storage of medications can all be to blame for why some dogs still get heartworms on medication.

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