Cat Deworming Shot vs Injection: What to Know
By Dr. Zubair Khalid, DVM, MS, PhD ·
A cat deworming shot is an injectable deworming medication that a veterinarian gives under the skin or into the muscle. It is not the right choice for every parasite, and it is not the same as the dewormers you buy at a pet store. This article explains which dewormers come as injections, when a shot makes more sense than a pill or a topical product, and what to watch for afterward.
This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- Injectable dewormers exist, but they only treat certain parasites. Most cat deworming shots target roundworms and hookworms, not tapeworms or coccidia.
- A shot is usually chosen when a cat will not take a pill, when a cat vomits oral medicine, or when a veterinarian wants to be sure the full dose was absorbed.
- The veterinarian calculates the dose from your cat's weight and health, so the amount given is specific to your cat.
- Side effects are usually mild and short lived, such as soreness at the injection site, sleepiness, or a brief upset stomach.
- A shot does not replace testing. Fecal testing helps confirm which parasite is present, and a follow-up sample may be needed after treatment [1].
What Is a Cat Deworming Shot?
A cat deworming shot is a liquid deworming drug delivered by injection instead of by mouth or on the skin. In the United States, the most common injectable dewormers for cats are used to kill roundworms and hookworms. These are the worms most often found in kittens and in cats that go outdoors or hunt.
Not every dewormer comes in injectable form. Praziquantel, which treats tapeworms, is typically given as a pill or an injection, and some products combine drugs to cover more than one parasite. Your veterinarian decides which drug and which form fit your cat.
The reason this matters is that owners often ask for "the deworming shot" as if one injection covers everything. It does not. A shot that clears roundworms will not clear tapeworms, and it will not treat coccidia, which is a single-celled parasite instead of a worm. If your cat has more than one parasite, the treatment plan may include more than one product.
Deworming also matters beyond the worms themselves. Kittens with intestinal parasites may respond differently to vaccination, and current guidance supports deworming before vaccines are given [2]. If you want the bigger picture on products and timing, see Deworming Medicine For Cats.
How Does an Injectable Dewormer Work?
Most injectable dewormers for cats work by interfering with the parasite's nervous system or energy metabolism. The worm loses the ability to move, feed, or stay attached to the intestinal wall, and it is passed out in the stool. The drug acts on the parasite, not on your cat's nerves, which is why the side effects in cats are usually mild.
The injection is typically given under the skin (subcutaneously) or into a muscle. Absorption is fast, and the drug reaches the parasites in the gut within hours. That speed is one reason a shot can be useful in a cat that is vomiting or refusing food, since there is no pill to keep down.
Injectable dewormers treat adult worms living in the intestine at the time of treatment. They do not kill parasite eggs in the environment, and they do not prevent reinfection. If your cat hunts rodents or lives with fleas, reinfection is possible, and repeat treatment or a monthly preventive may be recommended.
Which Cats Get a Deworming Injection Instead of a Pill?
Veterinarians reach for an injectable dewormer in a few common situations.
Cats that will not take oral medicine. This is the most frequent reason. Some cats are experts at spitting out pills, and a shot removes the daily struggle.
Cats that vomit pills or liquid dewormers. If oral medicine comes back up, the dose is lost. An injection avoids that problem.
Kittens and young cats. Young cats are more likely to carry roundworms, and a veterinarian may prefer an injection to be certain the full dose is delivered.
Cats with heavy or mixed infections. When a fecal test shows more than one parasite, the plan may combine an injection with an oral or topical product.
Cats in shelters or group settings. Deworming is common in shelter populations because intestinal parasites spread easily where many cats share space [1].
Ease of administration is a real factor in how veterinarians choose parasite products, and client preference influences the decision in many cases [3]. If you know your cat is impossible to pill, say so. Your veterinarian can factor that into the plan.
Dosing Basics for Injectable Dewormers
Who decides the dose
Your veterinarian does. The dose depends on your cat's body weight, the specific drug, and your cat's overall health. Never use a dose meant for a dog, and never split a dose based on a guess about your cat's weight. A kitten and an adult cat can differ by several pounds, and that difference changes the correct amount.
How the injection is given
The injection is given in the clinic, usually under the skin over the shoulders or into a muscle in the hind leg. Most cats tolerate it well. Some clinics use a small needle, and the whole visit takes only a few minutes.
What to do about a missed dose
If your cat was scheduled for a repeat injection and you miss the appointment, call the clinic. Do not try to make up for it by giving an oral dewormer at home unless your veterinarian tells you to. Timing between doses matters, and your veterinarian will tell you when to reschedule.
Follow-up testing
A single treatment does not always clear every parasite. In one shelter study, fecal samples were collected again after deworming to check what remained [1]. Your veterinarian may ask for a follow-up fecal sample, especially if your cat still has diarrhea or if the first test showed a parasite that is hard to clear.
Side Effects of a Deworming Shot for Cats
Most cats have no reaction beyond a brief pinch at the injection site. When side effects do happen, they are usually mild and pass within a day or two.
| Side effect | How common or serious | What to do |
|---|---|---|
| Soreness or small swelling at the injection site | Common, mild | Leave it alone. Call the clinic if it grows, drains, or lasts more than a few days. |
| Sleepiness or quieter behavior | Common, mild | Let your cat rest. Call if it lasts more than 24 hours. |
| Vomiting or soft stool | Uncommon, usually mild | Offer water and small meals. Call if vomiting repeats or your cat stops eating. |
| Drooling or nausea right after the visit | Uncommon, mild | This often passes in minutes. Call if it continues. |
| Facial swelling, hives, trouble breathing | Rare, serious | This is an emergency. Seek veterinary care right away. |
| Weakness, wobbliness, or tremors | Rare, serious | Call your veterinarian or a poison control line immediately. |
Severe reactions to dewormers are uncommon, but they can happen. If you have ever watched a cat after a vaccine, the pattern is similar. Mild lethargy is different from a true allergic reaction, and the difference matters. For a side-by-side comparison of mild and serious reactions, see Vaccine Reactions in Dogs and Cats: Anaphylaxis vs Mild Lethargy Triage.
Who Should Not Get a Deworming Shot?
Injectable dewormers are not right for every cat. Tell your veterinarian about your cat's full history before any injection.
Cats that are sick or weak. A cat with a fever, severe dehydration, or an ongoing illness may need to stabilize first. Deworming before vaccination is generally recommended, but the cat still needs to be well enough for treatment [2].
Underweight or very young kittens. The dose depends on weight, and a kitten who is small for age needs a careful calculation. Your veterinarian will decide whether an injection or a gentler oral product is safer.
Cats with known drug reactions. If your cat reacted badly to a dewormer before, say so. The veterinarian can choose a different drug class.
Pregnant or nursing cats. Some dewormers are not labeled for use during pregnancy. Your veterinarian will pick a product that fits your cat's situation.
Cats on other medications. Tell the clinic about every drug, supplement, and topical product your cat receives. Some products interact, and combining dewormers without guidance can raise the risk of side effects.
Overdose and When to Call for Help
An overdose of a dewormer can cause vomiting, drooling, wobbliness, tremors, or seizures. This is most likely when a cat gets a dose meant for a larger animal, or when two deworming products are given close together without veterinary guidance.
If you think your cat received too much dewormer, call your veterinarian right away. If the clinic is closed, call a pet poison control line. In the United States, you can reach the ASPCA Animal Poison Control Center at (888) 426-4435 or the Pet Poison Helpline at (855) 764-7661. Both may charge a consultation fee.
Do not wait for symptoms to appear before calling. Early treatment is easier and safer than treating a cat who is already having tremors. Bring the product packaging or the name of the drug with you if you go to the clinic.
Limitations and When to Contact a Veterinarian
No article can tell you what is happening with your individual cat. Your veterinarian needs to examine your cat, review the fecal test results, and weigh your cat to choose the right treatment.
Call the same day if:
- Your cat vomits more than once after the injection.
- Your cat refuses food for more than 24 hours.
- The injection site is swollen, warm, or painful.
- Your cat seems weak or unusually quiet and does not improve.
Go to an emergency clinic now if:
- Your cat has trouble breathing, swelling of the face, or hives.
- Your cat has tremors, seizures, or cannot stand.
- Your cat collapses or becomes unresponsive.
Schedule a routine visit if:
- Your cat still has diarrhea or visible worms in the stool after treatment.
- You need a follow-up fecal test.
- You want to set up a monthly parasite prevention plan.
If your cat needs fluids or other at-home care after a visit, this guide can help: How to Give Your Cat Subcutaneous Fluid Injections at Home.
Frequently Asked Questions
How much does a cat deworming shot cost?
Costs vary by clinic, region, and the specific drug used, so there is no single national price. The visit often includes an exam fee plus the medication charge. Call your clinic for an estimate, and ask whether a fecal test is included.
Is a deworming shot better than a pill?
Neither is automatically better. A shot guarantees the dose was given, which helps with cats that spit out pills or vomit them. A pill may be the better choice when the parasite requires a drug that only comes in oral form.
Can my cat get worms again after the shot?
Yes. The injection kills worms living in your cat at the time of treatment. It does not prevent new infections from fleas, hunting, or contaminated soil. Monthly prevention and flea control lower the risk.
Do indoor cats need deworming?
Sometimes. Indoor cats can still pick up parasites from fleas, from soil tracked in on shoes, or from a new cat in the home. Your veterinarian can help you decide based on your cat's lifestyle and risk factors.
How long does it take for the shot to work?
Most injectable dewormers start acting within hours, and worms are usually passed within a day or two. If you still see worms after that window, call your veterinarian, because a second treatment or a different drug may be needed.
If your cat has been treated for worms and you are also dealing with litter box changes, this article can help you sort out what you are seeing: Cat Spraying vs. Urinating: How to Tell the Difference and What to Do.
Related Articles
- Cat Spraying vs. Urinating: How to Tell the Difference and What to Do
- Deworming Medicine For Cats
- Vaccine Reactions in Dogs and Cats: Anaphylaxis vs Mild Lethargy Triage
- Roundworm Treatment for Cats: Safe Dewormers and Prevention
- How to Give Your Cat Subcutaneous Fluid Injections at Home
- Cat Vaccination Schedule: Which Shots Are Essential for Your Cat?
- Cat Deworming Side Effects: What to Expect
- How Often Should Cats Be Dewormed? Indoor and Outdoor Schedule
- Is Cat Dewormer Over the Counter? Safe Options and Risks
- Toxocara cati Roundworm Infection in Cats and Kittens: Prenatal Transmission and Clinical Management
- Intestinal Parasites in Dogs and Cats: Identification, Symptoms, and Treatment Options
References
- Prevalence of enteropathogens and endoparasites in cats at an animal shelter in Ontario. The Canadian veterinary journal = La revue veterinaire canadienne, 2025.
- Antibody response after feline panleukopenia virus vaccination in kittens with and without intestinal parasites. Journal of feline medicine and surgery, 2024.
- Factors influencing feline antiparasitic prescriptions by veterinarians and demographics across parts of the UK. Veterinary record open, 2026.