# Dog After Worming Tablet: Side Effects and Care Most dogs feel completely normal after a worming tablet, and any upset stomach usually settles within a day. A small number of dogs vomit, seem tired, or have loose stool for a short time. Serious reactions are uncommon, but they do happen, and they are more likely in certain breeds, in puppies, and when too much medicine is given. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Mild vomiting, soft stool, drooling, or a day of low energy are the most common complaints after deworming, and they usually pass on their own. - Never give a second dose because your dog threw up or seemed "off." Call your veterinarian first. - Collies, Australian Shepherds, Shelties, and other herding breeds can carry the MDR1 gene and may react badly to some dewormers. Tell your vet your dog's breed before treatment. - Signs of a real emergency include tremors, wobbling, seizures, blindness, or collapse. These need immediate care. - If you think your dog got too much medicine, call your veterinarian or a pet poison hotline right away, even if your dog looks fine. ## What Dewormers Are and Why Veterinarians Use Them A dewormer is a medicine that kills or expels intestinal worms and, in some products, other parasites. The worms that matter most in US dogs are hookworms (Ancylostoma caninum and Uncinaria stenocephala) and roundworms (Toxocara canis). Both are common, and both can infect people, which is one reason routine deworming matters for public health as well as for your dog [1][2]. Many modern products are combinations. A single chewable tablet may contain one drug for fleas and ticks, one for heartworm prevention, and one or two for intestinal worms. Examples include tablets built around moxidectin plus pyrantel, sometimes with praziquantel, lotilaner, or fluralaner added [1][3][4]. Your veterinarian picks the product based on your dog's age, weight, lifestyle, region, and risk of heartworm and intestinal parasites. Some products are also used to prevent heartworm disease, a potentially fatal infection spread by mosquitoes. In laboratory and field studies, combination tablets containing moxidectin prevented heartworm infection when given at the labeled dose [4]. Because heartworm prevention depends on steady dosing, your veterinarian may also discuss yearly testing. Current guidance treats prescribing heartworm preventives without antigen testing as not recommended, regardless of how reliably you have dosed your dog [5]. ## How Dewormers Work Different dewormers work in different ways, but the goal is the same: remove the parasites without harming your dog. Pyrantel, a common ingredient, paralyzes worms so the body can pass them out. Moxidectin, a macrocyclic lactone, interferes with the parasite's nervous system and is used for both intestinal worms and heartworm prevention [3][4]. Praziquantel targets tapeworms. Lotilaner and fluralaner kill fleas and ticks. When these drugs are combined, studies confirm they do not interfere with each other's effectiveness against the target parasites [2][4]. The drug has to be absorbed, distributed through the body, metabolized, and excreted. How fast that happens depends on the drug, the dose, and the route it was given. That same pharmacology is why some dewormers carry withdrawal times in food-producing animals, a concern for livestock but not for your pet dog [6]. ## Dosing Basics: Who Decides and What to Do If You Miss a Dose Your veterinarian calculates the dose from your dog's body weight and health status. Do not split, guess, or borrow a dose from another pet. Weight-based dosing is not optional with these drugs. Puppies in particular gain weight quickly, and a dose that was right last month may be too low now. Give the tablet as directed, with or without food depending on the product. Some dogs eat chewables happily. Others need the tablet hidden in a small treat or placed in the back of the mouth. If your dog spits it out, do not assume any was swallowed. If you miss a dose, do not double up. Call your veterinary clinic and ask how to restart the schedule. For heartworm preventives, gaps in dosing matter because the drug works by killing larvae before they mature, and a missed month can leave a window of risk [4][5]. ## Dog After Worming Tablet: Common and Serious Side Effects Most reactions are mild and short. A smaller number are serious and need prompt care. The table below separates the two. | Side effect | How common or serious | What to do | |---|---|---| | Vomiting | Common and usually mild | Withhold food for a few hours, offer small amounts of water. Call your vet if it repeats or lasts more than a day. | | Diarrhea or soft stool | Common and usually mild | Keep water available. Call if there is blood, if it is severe, or if it lasts beyond 24 to 48 hours. | | Lethargy or sleepiness | Common and usually mild | Let your dog rest. Call if your dog will not stand, will not eat, or seems worse instead of better. | | Drooling, lip licking, nausea | Common and usually mild | This often means an upset stomach. Offer water and watch closely. | | Loss of appetite | Fairly common and usually mild | Offer a small bland meal later. Call if your dog refuses food for more than a day. | | Itching, hives, facial swelling | Uncommon and serious | This can be an allergic reaction. Call your vet right away. | | Tremors, wobbling, unsteady walk | Uncommon and serious | This can signal neurologic toxicity. Seek veterinary care immediately. | | Seizures, blindness, collapse | Rare and an emergency | Go to a veterinary emergency hospital now. | If your dog vomits shortly after the tablet, the medicine may not have been absorbed. Do not repeat the dose on your own. Your veterinarian can advise whether to redose, wait, or switch products. If vomiting happens after other medicines too, our guide on [what to do if your dog vomits after taking medication](/knowledge/veterinary-medicine/pet-medication-guide/dog-vomits-after-medication) walks through the same steps. Some owners notice a cough after starting a heartworm preventive and worry it is related. That is covered in our article on [whether a dog's cough is a side effect of heartworm medication](/knowledge/veterinary-medicine/pet-medication-guide/dog-cough-heartworm-medication-side-effect). ### Dog Sick After Worming Tablet: What It Usually Means When a dog is sick after a worming tablet, the cause is usually a mild stomach upset from the medicine itself. Nausea, drooling, one episode of vomiting, or a soft stool the next morning are the typical pattern. These signs often resolve within 24 hours without treatment. A few situations deserve more attention. If your dog was already carrying a heavy worm burden, dying worms can cause some GI upset as they pass. If your dog is a puppy, very small, or already ill, the same dose that suits an adult dog can hit harder. And if your dog has reacted to a dewormer before, that history matters. ### Dog Lethargic After Deworming A dog that is a little quiet and sleepy for a day after deworming is a common report. True lethargy is different. Watch for a dog that will not get up, will not eat or drink, seems disoriented, or is getting worse instead of better. Those signs are not expected and should be checked the same day. ### Dog Vomiting After Worming One vomit right after the tablet is often just the tablet coming back up. Repeated vomiting, vomiting with blood, or vomiting along with weakness is a different story. Call your veterinarian if vomiting happens more than once, lasts past a day, or comes with any neurologic sign. ## Who Should Not Take These Medicines, and What Interacts With Them Dewormers are not one-size-fits-all. Your veterinarian will weigh several factors before prescribing. ### The MDR1 Gene and Herding Breeds Some herding breeds, including Collies, Australian Shepherds, Shelties, and related mixes, carry a mutation often called the MDR1 gene. Dogs with this mutation can have trouble clearing certain drugs, including some macrocyclic lactones such as ivermectin and moxidectin, out of the brain. The result can be neurologic signs like tremors, wobbling, or seizures at doses that other dogs tolerate. This is why breed matters, and why you should always tell your veterinarian what breed or mix your dog is. ### Age, Weight, and Pregnancy Very young puppies, dogs under the labeled minimum weight, and pregnant or nursing dogs may need a different product or a delay. Labeled minimums exist for a reason. In one heartworm prevention study, dogs had to be at least 8 weeks old and weigh at least 1.5 kg to be enrolled [4]. Your veterinarian applies the same kind of limits to your dog. ### Other Medicines Tell your veterinarian about everything your dog takes, including flea and tick products, heartworm preventives, antibiotics, seizure medicines, and supplements. Combining products that contain the same drug can accidentally double the dose. If your dog is on a flea and tick product and you are adding a dewormer, our article on [flea and tick medicine side effects in dogs](/knowledge/veterinary-medicine/parasitic-diseases/flea-and-tick-medicine-for-dogs-side-effects) explains what to watch for. If your dog is also on antibiotics, see [what the side effects of antibiotics in dogs are](/knowledge/veterinary-medicine/pet-medication-guide/dog-antibiotics-side-effects), since stomach upset can have more than one cause. ## Overdose and When to Call a Veterinarian or Poison Control Overdose is the situation that worries veterinarians most, because it is the most likely to cause serious signs. It happens when a dog eats multiple tablets, when a chewable is left within reach, when two products with the same ingredient are given together, or when a dose meant for a large dog is given to a small one. Signs of too much dewormer can include heavy drooling, repeated vomiting, tremors, unsteady walking, dilated pupils, blindness, seizures, and collapse. These are not wait-and-see signs. If you suspect an overdose, call your veterinarian or a pet poison hotline immediately, even if your dog seems fine. Have the product name, the strength, the number of tablets, your dog's weight, and the time of exposure ready. Do not induce vomiting unless a veterinarian tells you to. ## Limitations and When to Contact a Veterinarian This article covers general patterns, not your individual dog. Every case needs a veterinarian who can examine your pet, ask questions, and decide on treatment. Call your veterinarian the same day if your dog vomits more than once, has diarrhea with blood, refuses food for more than a day, seems painful in the belly, or is much sleepier than usual. Go to an emergency clinic now if you see tremors, wobbling, seizures, blindness, collapse, difficulty breathing, or swelling of the face and throat. Schedule a routine visit if the mild signs linger past a couple of days, if you are unsure the tablet was swallowed, or if you want to switch to a product that suits your dog better. If your dog has recently had a vaccine and now has loose stool, our article on [dog diarrhea after vaccination](/knowledge/veterinary-medicine/digestive-and-urinary-care/dog-diarrhea-after-vaccination) can help you sort out what is likely related. ## Frequently Asked Questions ### How long do dewormer side effects last in dogs? Most mild signs, such as drooling, one vomit, or a day of low energy, settle within 24 hours. If signs are still present after a day or two, or if they are getting worse, call your veterinarian. ### Should I feed my dog after giving a worming tablet? Follow the label and your veterinarian's instructions, since some products are given with food and others are not. If your dog has an upset stomach, offer water first and a small bland meal once vomiting has stopped. ### Can I give my dog a second worming tablet if it vomited the first one? No. Do not repeat the dose on your own. Call your veterinarian, who can decide whether the medicine was absorbed and whether redosing is safe. ### Are dewormers safe for puppies? Puppies are dewormed routinely, but the product and dose must match their age and weight. Very young or very small puppies may not meet the labeled minimums for some products, so your veterinarian chooses what fits. ### Can my dog still have worms after deworming? Yes, sometimes. Dewormers kill the worms present at the time of treatment, but reinfection is easy if your dog walks where other animals defecate or eats contaminated soil. Repeat treatment and prevention are set by your veterinarian based on your dog's risk. ## Related Articles - [How to Tell If Your Dog's Cough Is a Side Effect of Heartworm Medication](/knowledge/veterinary-medicine/pet-medication-guide/dog-cough-heartworm-medication-side-effect) - [Flea And Tick Medicine For Dogs Side Effects](/knowledge/veterinary-medicine/parasitic-diseases/flea-and-tick-medicine-for-dogs-side-effects) - [What Are the Side Effects of Antibiotics in Dogs?](/knowledge/veterinary-medicine/pet-medication-guide/dog-antibiotics-side-effects) - [Dog Diarrhea After Vaccination: Normal or a Concern?](/knowledge/veterinary-medicine/digestive-and-urinary-care/dog-diarrhea-after-vaccination) - [What to Do If Your Dog Vomits After Taking Medication](/knowledge/veterinary-medicine/pet-medication-guide/dog-vomits-after-medication) - [Side Effects Of Flea Medicine For Dogs](/knowledge/veterinary-medicine/parasitic-diseases/side-effects-of-flea-medicine-for-dogs) - [Dog Deworming Side Effects: What's Normal and What's Not](/knowledge/veterinary-medicine/pet-medication-guide/dog-deworming-side-effects) - [Vomiting in Dogs After Deworming: Normal or Not?](/knowledge/veterinary-medicine/digestive-and-urinary-care/vomiting-after-deworming-dogs) - [Worms After Deworming: What to Expect in Puppy Poop](/knowledge/veterinary-medicine/parasitic-diseases/worms-after-deworming-puppy-poop) - [Canine Parasitic Vomiting: Identifying Worms in Dog Vomit and Gastrointestinal Implications](/knowledge/parasites/pet-parasites/canine-parasitic-vomiting-identifying-worms-dog-vomit-gastrointestinal-implications) ## References 1. [Field efficacy and safety evaluation of a novel chewable tablet (Credelio Quattro™) containing lotilaner, moxidectin, praziquantel, and pyrantel against gastrointestinal nematode infections in dogs in the USA](https://pubmed.ncbi.nlm.nih.gov/40713857/). Parasites & vectors, 2025. 2. [Efficacy of a novel chewable tablet (Credelio Quattro™) containing lotilaner, moxidectin, praziquantel, and pyrantel for the treatment and control of hookworm infections in dogs](https://pubmed.ncbi.nlm.nih.gov/40176170/). Parasites & vectors, 2025. 3. [Efficacy evaluation of a new oral chewable tablet containing fluralaner, moxidectin, and pyrantel (BRAVECTO® TriUNO) against hookworm and Toxascaris leonina infections in a non-terminal study design in dogs](https://pubmed.ncbi.nlm.nih.gov/41634831/). Parasites & vectors, 2026. 4. [Efficacy of a novel chewable tablet (Credelio Quattro™) containing lotilaner, moxidectin, praziquantel, and pyrantel for the prevention of heartworm disease (Dirofilaria immitis) in dogs](https://pubmed.ncbi.nlm.nih.gov/41943128/). Parasites & vectors, 2026. 5. [Is annual Dirofilaria immitis antigen testing at preventive renewal proportionate to the residual infection risk in documented-compliant dogs?](https://pubmed.ncbi.nlm.nih.gov/42542127/). Journal of the American Veterinary Medical Association, 2026. 6. [Withholding Periods After Anthelmintic Treatment in Animals - Pharmacology](https://www.merckvetmanual.com/pharmacology/anthelmintics/withholding-periods-after-anthelmintic-treatment-in-animals). Merck Veterinary Manual. ## Further Reading - [American Veterinary Medical Association: First Aid Tips for Pet Owners](https://www.avma.org/resources-tools/pet-owners/emergencycare/first-aid-tips-pet-owners) - [Merck Veterinary Manual: Dog Owners](https://www.merckvetmanual.com/dog-owners) - [Cornell Richard P. Riney Canine Health Center: Canine Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information)