Last updated Apr 5, 2026
Kirsten McCarthy / Cats.com
Fenbendazole is a broad-spectrum dewormer commonly used in veterinary medicine to treat pets for a variety of nematode (worm) and protozoal parasites. Common brands include Panacur and Safe-Guard.
In this article, you’ll learn what fenbendazole is, how it works, and the types of parasites in cats it may be used for, as well as some frequently asked questions.
Fenbendazole for Cats Overview
About Fenbendazole for Cats
Fenbendazole is classified as a benzimidazole antiparasitic agent and has a very wide range of effect against a variety of internal parasites.
Microtubules are structures within cells that assist in transport of materials within the cells. Fenbendazole acts to disrupt this transport system in affected parasites. At higher doses, it may also disrupt metabolic enzymes and pathways of affected parasites.
What Does Fenbendazole Do for Cats?
Fenbendazole can have efficacy against a variety of internal parasites commonly found in cats, including roundworms, hookworms, whipworms, lungworms, the protozoal parasite Giardia, and several others.
While it is helpful to know what fenbendazole does treat, it is also important to be aware of what it does not treat.
While it can be used to treat tapeworms, this is only for tapeworms of the Taenia species. Dipylidium caninum, which is more commonly seen in cats when they ingest a flea, requires a different dewormer for treatment.
Fenbendazole also does not have efficacy against coccidian parasites like Cystoisospora (Isospora) species, which may sometimes be seen in a cat’s stool sample and/or cause gastrointestinal disease.
It is not effective against Toxoplasma gondii, which causes toxoplasmosis, the disease human physicians often counsel pregnant women about in regards to avoiding contact with a litter box or cat feces during pregnancy.
Heartworms, which are not intestinal worms, but are transmitted by mosquitoes and dwell in the major vessels near the heart as well as the heart chambers themselves, are not affected by fenbendazole. While not covered here, there is no approved treatment for heartworms in cats.
Side Effects of Fenbendazole for Cats
Some cats may experience temporary diarrhea while taking fenbendazole. Kirsten McCarthy / Cats.com
At appropriate dosages, fenbendazole does not typically cause any adverse reactions on its own. Infrequently, drooling, vomiting, or diarrhea may occur.
It is important to remember that the job of any dewormer is to kill internal parasites. This means that sometimes, a reaction may occur to components released by a dying parasite, especially in cases where a very high parasite load is present.
In these cases, drooling, vomiting, diarrhea, or GI discomfort may be more likely to be seen. Typically, these signs are temporary, but if concerning, should be reported to an attending veterinarian in case some supportive care is needed.
If you are ever concerned that your kitty may have developed side effects while using fenbendazole, or if an overdose is suspected, make sure to immediately contact one or more of the following for advice:
- Your veterinarian
- ASPCA Animal Poison Control Center (1-888-426-4435)
- Pet Poison Helpline (1-855-764-7661)
Fenbendazole for Cats Dosage
Your veterinarian will tell you the proper dosing for fenbendazole, which is determined by weight. Melina Grin / Cats.com
While it is FDA approved for use in dogs, fenbendazole is not labeled for use in cats and all dosing is considered extra-label in kitties.
For this reason, any products labeled only for dogs, including over the counter products like Safe-Guard, should be reviewed first with your vet to determine what dose will work best for your cat.
Dosing depends on body weight. Duration of treatment with fenbendazole depends on the type of parasite, where it may be used for anywhere from three to up to 10 or more consecutive days.
Remember that not all digestive disturbances are caused by intestinal parasites and fenbendazole does not treat for all potential parasites. Any use of a dewormer should be based on results of a fecal/stool sample or otherwise as directed by a veterinarian.
Fenbendazole only comes in powder or liquid suspension forms that are appropriate for use in small animals. The powder can be tricky to properly portion out and dose for some smaller cats and kittens, another reason to refer to your vet for proper instructions.
The liquid oral suspension requires a prescription, but comes in a 1 liter bottle size, making it impractical as a choice for a single treatment course. Veterinary practices typically dispense individual doses or smaller dosage volumes to use for treating a cat or kitten for susceptible parasites.
The syringe paste intended for use in horses is also impractical to use in cats, as they typically require doses much smaller than the increments on the syringe.
Interest in Fenbendazole for Cancer Therapy
In the last couple of years, there has been increased interest in benzimidazoles, more specifically, fenbendazole, for properties that may help to kill cancer cells. The same mechanism of action that makes fenbendazole potent against parasites has been shown in some laboratory studies to have similar effects on cancer cells.
Microtubules are structures very important for several cell functions, including dividing and multiplying. Fenbendazole acts as a microtubule destabilizing agent and has action against several other cellular pathways.
While fenbendazole shows some promise and potential in future anti-cancer therapies, experts are still in the earliest stages of understanding its benefits for certain cancers in people as well as safety parameters for its use. To date, there have been no clinical trials in humans or pets, only observations on cell cultures in a lab setting. There is a very big difference between how a medication may behave towards cells in a lab and the effects it may have on cells in the body.
Interest in fenbendazole’s potential use for cancer treatment has caught the attention of many, especially on social media, which has led people to self-medicate with the deworming product labeled only for use in some animals.
Much of this stemmed from a man with small-cell lung cancer who claimed in 2016 that taking fenbendazole directly contributed to his cancer going into remission. What often goes unmentioned is that the man was on conventional cancer treatment under the care of an oncologist at the same time.
This story still led to a craze of people buying fenbendazole to self-medicate. The effects have not been consistently positive.
In 2019, Korean oncologists documented one particular case of an 80-year-old woman who developed severe liver toxicity after taking fenbendazole for several months. And a Korean celebrity who initially touted fenbendazole’s benefits for cancer reneged on these claims several months later, saying it was ineffective.
While the safety of fenbendazole has been far better established in animals, including pets, its use for cancer is just as unfounded and there is no established dose for cancer treatment.
It is used safely for up to one month for some deworming protocols. But there are no studies on the effects of using fenbendazole every day for extended periods of months or years or that these protocols work for cancer.
Oncologists also point out that the mechanism of microtubule destabilization is not unique to febendazole. There are other existing chemotherapy medications that work by this same method.
As Sheila Singh, director of McMaster University’s Centre for Discovery in Cancer Research, says, “Seeing promising data in a dish of cancer cells is the beginning, but to say that something could cure cancer is unscientific because there’s no data that backs that claim up whatsoever.”
Preliminary research is promising, to be sure. But there is still no concrete evidence that fenbendazole is an effective anti-cancer treatment and should never be used in lieu of accepted and conventional cancer therapy approaches.
Vets who will not consent to prescribing fenbendazole for this purpose are not trying to deny access to a miracle cancer cure. They are trying to focus efforts on evidence-based approaches that have documented benefits.
Some vets may suggest the use of fenbendazole in terminal patients because of the perception that it won’t hurt. This may be true. Just remember that its use for that purpose is very off-label, with little evidence to support that use at this time.
But hopefully, the future holds great promise with further research.
Conclusion
Kirsten McCarthy / Cats.com
Fenbendazole is a very effective and safe broad-spectrum dewormer used commonly to treat cats and kittens for a variety of internal parasites. It is important to remember however that it does not treat all parasites, and not all digestive disturbances are caused by parasites. That’s why it’s important to work with your veterinarian to determine if using fenbendazole is appropriate.
Drug Dosing Disclaimer: We are only able to provide doses for medications that are FDA approved for use in cats and only as the label guidelines dictate. For medications that are used off-label we can only provide guidelines and safety information for use. Safe and appropriate dosing for off-label medications can only be determined by a primary care veterinarian.
We encourage you to work with your veterinarian to determine if a particular medication is appropriate for your cat. Changing or adjusting a dose for your cat on your own without consulting with a veterinarian can carry risk. We do not encourage use of medications prescribed for human use in pets without first consulting with a primary care veterinarian.
Frequently Asked Questions
How much fenbendazole can I give my cat?
The dosage amount will depend on your cat’s weight and the form of fenbendazole available. To ensure proper dosing, as well as to confirm whether or not fenbendazole is appropriate to give your cat, it’s best to talk to your veterinarian.
Is fenbendazole safe for cats?
Yes, fenbendazole is generally deemed very safe for cats. On occasion, some mild digestive upset may occur. Digestive upset may be more common when fenbendazole is used to treat cats with high parasite loads and the dying parasites cause disturbance in the body.
Can cats be dewormed with fenbendazole?
Yes, although it depends on what worms a cat is infected with. Use of a dewormer should always be based on a stool/fecal sample or similar testing for the presence of parasites. In cats, fenbendazole is most effective against roundworms, hookworms, lungworms, and the protzoal parasite Giardia.
How do you give fenbendazole to a cat?
This depends on the form being used. If you have been provided with the powder form, it’s often easiest to give to a cat mixed with wet or soft food, both to hide the taste, but also because it may be more effective when given with food.
If you have the liquid suspension form, it may also be mixed with wet or soft food if your kitty will take it that way. However, it may need to be administered directly by mouth with a syringe that your veterinarian should provide you. This is especially the case with small cats and kittens.
If you have difficulty administering fenbendazole to your cat, make sure to touch base with your vet to discuss additional ideas, see if a different dewormer may be effective, or to set up an appointment for veterinary staff to administer the dewormer for you.
Not helpful!
Hi Fred, sorry to hear that. Let us know if there’s anything we can do to help.
My cat, only 4 years old and 10 lbs, has been diagnosed with cancer in the neck of his bladder; inoperable! He’s already taking Metacam. I have ordered CBD oil from Penelope’s Bloom and would like to start him on Fenben, as well. What is the recommended dosage? Also curcumin! Do you have any recommendations? My vet was ready to euthanize him, right after diagnosis; he’s playful and happy to be alive! We love this beautiful boy so much, but will NOT allow him to suffer. As long as he has quality of life, we want to keep him happy and alive! Thanks so much, it’s not easy to type while crying!
Hi Terry,
I’m very sorry to hear about your kitty. If this is truly a bladder neck tumor like transitional cell carcinoma, surgery in that area is often not a great benefit compared to the complications and risks of trying to do it. On top of the risk of scar tissue occluding the urethra and/or urinary incontinence that may result, the tumor may recur if margins aren’t possible.
If you feel your cat’s quality of life is still very good, I don’t feel it’s wrong to value the time you have together until something changes.
Be very vigilant with the metacam. NSAID medications can help slow down bladder tumors and are reasonable to consider but carry risks in cats as well.
I can’t advise a specific curcumin supplement, but it is important to look for a supplement that is actually curcumin and not just turmeric. Some turmeric supplements may have very little actual curcumin in them.
I’m a little puzzled by your interest in starting your cat on fenbendazole in relation to this disease as it does not have any anti cancer or anti-inflammatory properties that I’m aware of. It is simply a dewormer. Was there a specific reason for your desire to use it? Or perhaps you’re thinking of a different medication?
The vet is treating my 18 yo BFF the same because of a fast growing mouth ulcer that the vet thinks might be cancer. I bought the goat formula of fenbendazole. It is liquid and easy to dose by weight. My boy is only 14lbs so the dose is 3ml once a day. Just started 6 days ago.
Look up DR.Jones on utube and cancer. Aman deemed to go home n die after being told cancer stage 4.Began fenbensadole.He is 75 yrs old and cancer free. Veterinary secrets look it up on utube
. I have a ragdall cat who has been having upper respiratory issues ie runny nose sneezing etc for many months now. I have spoken to a vet gotten antibiotics and I also give him lysine 2x a day. I find that even missing one dose makes him all stuffed up. Is there no cure? Would fenbedazole help him? Is so how much
We have two cats both the same age. Our one 10yo 11 lb cat was just diagnosed with GI lymphoma via ultrasound. The vet was ready to euthanize him right a way too. After doing research we also came across fenben for treatment too as we are hearing so many good stories. We purchased the goat dewormer 100mg/ml. But now we are seeing our other cat with the same exact symptoms (vomiting blood, decreased appetite) and wondering is this really cancer?! Our cat was diagnosed one week ago with cancer, it is 3/8/25. And today our other cat started vomiting blood with decreased appetite for the past week which is how this all started with our other cat. I find it crazy both our cats could have cancer at the exact same time, unless this is contagious? But what i read its not. Any help would be so appreciated. We love our boys.
Hi Jeanna,
There are far better and more effective established treatments for GI lymphoma than fenbendazole. Despite what is available to read out there, fenbendazole is not a confirmed panacea for all kinds of cancers. There are only some limited case reports supporting further research may be promising. There are still no established dosing protocols or provided guidance on using it for this purpose. My concern is that given its low cost and the ease to acquire it, too many pet owners are going to use it as a sole treatment approach, losing valuable time that could be used to pursue more established and medically confirmed therapies. Really, you should speak to an oncologist at least about all the options available. Treatment approaches depend on whether it’s small cell or large cell lymphoma. Small cell has a better prognosis but large cell can unfortunately spread rather quickly. I wasn’t clear if you had any confirmatory testing.
For your other cat, you shouldn’t make any kinds of assumptions, as vomiting, even with blood, can have multiple causes. No, lymphoma is not contagious. But it’s very important to get a proper diagnosis. I mean if you have two older cats, it’s always possible they could both have GI lymphoma (I hope not), but it could just as easily be a bad flare up of inflammatory bowel, dietary indiscretion, or something else. An abdominal ultrasound could be really helpful.
You try so hard to explain and do so with patience. Thank you for your efforts.
Thank you, Ann, I do appreciate that. Kind regards.