By Dial A Vet Veterinary Team
A dewormer, or wormer, is a medicine that kills internal parasites in dogs. Walk into any pet shop and you will find tablets, chews, spot-ons and combination products that also cover fleas, ticks and heartworm, each listing a different set of parasites on the box. Choosing the wrong one can leave your dog unprotected against the worm that matters most where you live, and using the wrong product or weight band can make a dog sick. Here is how dewormers work and how to choose sensibly with your vet.
Key takeaways
- Dewormers kill worms already present. Most do not give long-lasting protection, so they are repeated on a schedule.
- Products differ in which worms they cover. Tapeworm and whipworm are the most common gaps.
- Heartworm prevention is separate unless the label specifically includes it.
- Always choose by your dog's current weight and follow the label exactly.
- Never use livestock, horse or cat products on dogs.
What dewormers target
- Roundworms (Toxocara and Toxascaris): very common in puppies.
- Hookworms (Ancylostoma and Uncinaria): blood-feeding worms, common in warmer regions.
- Whipworms (Trichuris vulpis): large bowel worms with very hardy eggs. Not covered by all products.
- Tapeworms (Dipylidium, Taenia and the hydatid tapeworm Echinococcus): need a product with tapeworm activity, often praziquantel.
- Heartworm (Dirofilaria immitis): spread by mosquitoes. Prevention products kill immature larvae before they reach the heart.
Types of dewormers
Allwormer tablets
Usually given every three months to adult dogs. Most cover roundworm, hookworm, whipworm and tapeworm, but check the label for each.
Monthly combination chews or tablets
Many cover fleas, ticks (including paralysis tick), heartworm and some intestinal worms. Coverage varies a lot between brands. Some do not include tapeworm.
Spot-on products
Applied to the skin, often combining flea and worm control. Be careful to use a dog product on dogs only and keep cats away until it dries, as some dog spot-ons are dangerous to cats.
Heartworm injection
Given by a vet, usually yearly, for heartworm prevention only. Intestinal worming is still needed separately.
How to choose with your vet
- Age: puppies need products labelled for their age and frequent treatment.
- Weight: weigh your dog. Products come in weight bands, and a guess can lead to under- or over-treatment.
- Lifestyle: rural, working, hunting or raw-fed dogs need reliable tapeworm cover because of hydatid disease.
- Location: paralysis tick areas along the east coast need tick protection, and heartworm prevention is recommended across most of Australia.
- Breed: collies, Australian shepherds, Shetland sheepdogs and related breeds may carry the MDR1 gene variant, which makes them sensitive to some parasite medicines. Tell your vet.
- Health: pregnant, nursing, elderly or unwell dogs need vet advice first.
Signs your dog may need worming
- Worms or segments in poo, vomit or on the fur
- Diarrhoea, sometimes with mucus or blood
- Pot belly, poor growth or dull coat in puppies
- Weight loss, low energy or pale gums
- Scooting
When to see a vet
Emergency now: tremors, wobbliness, dilated pupils, drooling or collapse after a parasite product (especially if a livestock product was used or a large amount was eaten), or a weak puppy with pale gums.
Same day: repeated vomiting or diarrhoea after worming, or a puppy that is unwell with worms.
Book a visit: worms that keep returning, uncertainty about which product to use, or before starting heartworm prevention in an adult dog with gaps in its history.
Using dewormers safely
- Follow the label for your dog's weight band and the treatment interval.
- Do not split or combine products unless your vet tells you to.
- Store chews out of reach. Flavoured products are tempting and dogs can eat a whole box.
- Never use horse, sheep or cattle wormers on dogs. Concentrated livestock products have caused serious poisoning in dogs.
- Keep a record of the product and date given.
How vets assess and treat
Your vet may test a faecal sample, run a heartworm test and review your dog's history before recommending a product. Some infections, such as whipworm or heavy roundworm burdens, need repeated treatment over several weeks. For a schedule overview see our worming Q&A.
FAQ
How quickly do dewormers work?
Many start killing worms within hours, and dead worms may pass over a day or two.
Do dewormers prevent future infection?
Most only kill worms present at the time, which is why they are repeated on a schedule.
Are pet shop wormers as good as vet products?
Many are effective. The key is choosing one that covers the right parasites for your dog and following the label.
Can dewormers make my dog sick?
Mild stomach upset can happen. Serious reactions are uncommon when products are used as labelled.
Talk with a vet
Unsure which product suits your dog? A Dial A Vet consult can help you compare options for your dog's lifestyle. Tremors, collapse or seizures after a parasite product need an in-person emergency vet immediately.
References
- Companion Animal Parasite Council (CAPC): General Guidelines for Dogs and Cats
- ESCCAP Guideline 01: Worm Control in Dogs and Cats
- Washington State University College of Veterinary Medicine: MDR1 Multidrug Sensitivity
- Australian Pesticides and Veterinary Medicines Authority (APVMA): Veterinary medicine labels and safe use
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. Always follow the label and your vet's advice when using parasite products.
