What happens if I give my dog dewormer but doesn't have worms?
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By Deanne
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February 17, 2026
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4 MIN READ
What do worming tablets actually do?
I’ve given my dog dewormer but I don’t think they have worms?
Possible side effects of unnecessary deworming
Can too much dewormer be dangerous?
When should I worry?
How often should you actually deworm your dog?
What are the signs that my dog has worms?
What should I do if I think my dog has worms?
We all want our dogs to be happy, healthy, and free of those nasty wriggly worms. Intestinal parasites can make your poor pup feel miserable and pose some health risks for us humans too. So, many of us are quick to use a deworming tablet at the first sign of trouble… or even “just in case.” But should you do this unless you are certain? Keep reading to find out the possible side effects and how to make sure your dog stays happy and healthy!
What do worming tablets actually do?
Worming treatments are medicines designed to get rid of internal parasites such as roundworms, tapeworms, whipworms, and hookworms. Dewormers target the worms, not your dog. They work in a few different ways, depending on the active ingredient — some paralyse the worms so they can be passed out in your dog’s poo, while others dissolve or kill them directly in the gut. The end result is the same: the worms die off, and your dog’s body gets rid of them.
I’ve given my dog dewormer but I don’t think they have worms?
In most cases, if your dog is otherwise healthy and you’ve used the correct dose of a vet-approved product, giving a dewormer when your dog doesn’t have worms won’t cause any major harm.
Dewormers are tested for safety in healthy dogs, and the active ingredients are designed to act on worms, not your dog. So if there are no worms present, the medication just passes through your dog’s system and does very little.That said, “no harm” doesn’t always mean "no effect". Some dogs are more sensitive to medications, and there can be mild side effects.
Possible side effects of unnecessary deworming
Even if your dog doesn’t have worms, the dewormer still goes through his digestive system and liver so mild side effects can still pop up. The most common ones include:
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Upset tummy. A bit of diarrhoea or loose stool for a day or so.
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Loss of appetite. Some dogs might skip a meal after taking it.
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Lethargy. Feeling a bit “off” or tired for a short while.
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Drooling or nausea. Especially if the tablet tasted unpleasant or was taken on an empty stomach.
These symptoms usually clear up quickly (within a day or two) and don’t require treatment. However, if your dog starts vomiting repeatedly, has blood in his stool, or seems genuinely unwell, it’s worth ringing your vet for advice.
Can too much dewormer be dangerous?
Yes. Just like with any medication, too much of a good thing can be harmful. Overdosing on dewormer can lead to vomiting, tremors, or even neurological symptoms in severe cases. Some breeds (like Collies, Australian Shepherds, and related types) are sensitive to certain worming drugs that contain ivermectin, so extra caution is needed there.
When should I worry?
While most dogs will be fine, there are a few situations where giving dewormer unnecessarily can cause issues:
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If the dose is wrong.
Deworming products must be dosed according to your dog’s exact weight. Giving too much can increase the risk of side effects, especially for smaller breeds. The Itch Wormer Tablets for Dogs are tailored perfectly to your pet to ensure safe and effective protection from worms.
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If your dog has a health condition.
Dogs with liver or kidney problems, for example, may have trouble processing certain medications, including dewormers.
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If the wrong product is used.
Not all dewormers are the same! Some are formulated for specific worms, species, or ages. Giving a cat dewormer to a dog (or vice versa) can be dangerous.
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If combined with other medications.
Some drugs don’t play nicely together and this includes a few dewormers. Always check with your vet if your dog is on any other meds.
How often should you actually deworm your dog?
In the UK, most vets recommend a routine deworming schedule rather than waiting until you think your dog has worms.
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Puppies: Every 2 to 3 weeks until 12 weeks old, then monthly until six months. Click here for a tailored puppy worming plan.
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Adult dogs: Usually every 3 months, though this can vary depending on lifestyle. It’s worth noting that a dog that spends lots of time outdoors, eats random things off the ground, or chases wildlife may need more frequent worming, whereas an indoor lapdog who never eats anything gross might get by with every 3 to 4 months.
It’s important to deworm your dog to their needs. Not sure how often to deworm your dog? Our Vet Team can help. Contact us here.
What are the signs that my dog has worms?
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A bloated belly (especially in puppies)
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Scooting or rubbing their bum on the ground
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Worms or segments visible in the poo (yep, gross but telling)
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Weight loss despite eating normally
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Dull coat or poor appetite
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Coughing (can happen with lungworms)
What should I do if I think my dog has worms?
Don’t panic. You need to promptly give your dog regular treatment to kill all the worms infesting their guts. You can treat your pet with tablets, spot-on or pastes. Itch Wormer Tablets for Dogs has a fast-acting formula that kills common dog intestinal worms and prevents newly hatched larvae from growing and multiplying. Protecting you, your family, your home and your dog from worms, until their next regular treatment. We will tailor the worming dose perfectly to your pet’s age, weight and lifestyle. Get started by telling us about your dog here.
It’s easy to overthink things when it comes to our pets, especially in an age when Google turns every sneeze into a crisis! But remember: worms are common, treatable, and preventable. Next time you’re tempted to give a tablet “just to be safe,” it’s worth asking: is it really necessary right now, or am I just worrying? Your dog will thank you either way!
Protect your pet from worms.
Intestinal worms can cause serious health issues for your pet and your family, but with a regular de-worming schedule you can protect your pet, home and family from these persistent parasites.
Itch Wormer tablets kills all common intestinal worms and prevent larvae from hatching and multiplying, until your pet's next regular treatment.
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