Dog Acting Weird After Flea Medicine Treatment: Possible Solutions & Fixes

dog acting weird after flea medicine

Our dog Claude is given a spot-on flea treatment every 4 weeks. We much prefer the spot-on liquid to flea pills as he always gags when he takes a tablet. However, in recent months we’ve been thinking about changing to an oral treatment, as our dog has been acting weird after his flea medicine. As soon as we apply the flea treatment, he goes absolutely crazy! It’s funny, but still very weird.

I wanted to try to understand why our dog acts all weird after his flea treatment, so spoke to a vet I know, plus some other dog owners to get some differing opinions.

I’ve also done some online research into it all – I hope you find it useful as there is even the possibility of an allergic reaction or poisoning. You can read more about the toxicity lower down the guide.

Our dog acts weird after his flea treatment

So, firstly, when I say acting weird after his flea medicine, what do I mean by that?

As a dog owner you will already know how the spot-on flea medicine is administered; With smaller dogs your part their fur at the top of the shoulder blade and squeeze the liquid from the tube. With larger dogs, you spot the treatment on in four places from their shoulders to the base of their tail.

And this is the point at which our dog Claude will start acting all weird.

We use Bayer Advantage (you can see the package in the photo below). As soon as the flea treatment medicine touches his skin, he goes crazy weird.

dog acting weird after flea treatment
This tick and flea treatment makes our dog go all weird and crazy!

The first thing he does is shake. I completely get that one, as he wants to get the spot-on liquid off his fur.

He will then start slinking on the ground before running at full pelt through the dog flap in our back door. He gets outdoors and run around in circles before rolling on the ground.

Having spoken to other dog owners, he is a small list of weird things they say their dogs do after being given a flea treatment:

  • Acting unsettled.
  • Tries to shake the treatment off.
  • Runs around.
  • Excessive scratching.
  • Rolls on the floor.
  • Starts to sulk.
  • Tiredness and lethargy.

Handy Hint: Here’s what dog fleas look like to the human eye.

What owners think the weird behavior could be?

I then asked the dog owners who have seen weird behaviour after a flea application why they believe this happens. Here’s a synopsis of the many reasons I heard on why they think their dog acts weird after flea treatment:

  • Dogs hate the smell of flea treatment as it can be very strong.
  • The flea treatment is strong enough to burn their skin a little.
  • Some dogs simply don’t like the sensation of medicine being applied.

The smell one makes sense to me. If you think about, dogs are said to have a sense of smell that is said to be 40 times greater than ours.

I know that if I use a hand sanitizer with strong alcohol in it, my dog will recoil when my hands go near him. They are definitely ultra-sensitive to very strong smells, and topical flea treatments can quite potent.

Then there’s the possible mild skin irritation that flea treatment can cause. According to the website, you can buy flea medicines for dogs with sensitive skin. Here’s what they say:

“Just like humans, dogs with sensitive skin can have uncomfortable reactions to certain medicines. Between breed, size, and age, no two dogs are the same. It shouldn’t be that big a surprise if your pup reacts badly to a flea medication that works effectively on the majority of pets.”

If you suspect your dog is acting weird after flea medicines due to a skin complaint, you could switch to a topical spot-on that is designed for dogs with sensitive skin or choose to swap to an oral flea pill instead.

The website says this about making the possible switch in how your dog takes his flea medicine:

“Oral treatments are a great alternative for dogs that have adverse reactions to topical treatment. Side effects of monthly pills or chewable tablets are rare, but can include nausea, diarrhea and hair loss. If your pet continues to react poorly to different kinds of flea treatments, contact your vet to figure out a way to keep your pet healthy while protecting it from fleas.”

Which flea treatment pill could be better?

Based on the assumption that it could be the topical flea treatment that is causing your dog’s weird reactions due to a burning sensation, you might want to try the oral alternatives. Here’s are two that I found on Amazon for small and large dogs:

Alternative solutions for sensitive skin

You could also switch to a flea treatment that is specifically designed for sensitive skin.

I searched through the comments and customer reviews online to see which flea treatment dog owners said was best for skin irritation, and the outright winner was Frontline Plus on Amazon.

With our own dog Claude, we also use a flea and tick collar. Many dog owners will use this as an alternative to spot-on treatments.

Handy Hint: Did you know that the effectiveness of flea treatment can depend on the natural oils in your dog’s coat, so you must not wash them out within 2 days of applying the medicine.

We find this really helps to keep the fleas and ticks at bay. We also have a cat and live in a forested area, so it’s an essential part of our doggy care. We actually double-up; flea collar and treatment just to be sure.

The flea and tick collar we use is the most renowned brand, Seresto. The collar is said to work for up to 8 months and means you don’t have any strong odor or need to apply messy monthly spot-on treatments – which could be the root cause of your dog acting weird.

To find out more about it and see whether it could work for your dog, check out the flea collar on Amazon.

Are natural flea treatments better for sensitive skin?

You might think that it’s worth trying a flea treatment with natural ingredients instead, but I would caution against it. Here’s what my vet friend said:

“Natural flea treatments can cause weird reactions in dogs too, and to be honest, they won’t be as effective either. I recommend dog owners use humanely tested flea medicines which are proven to work with scientific evidence. Dogs might hate the smell and feel, but this won’t last for long and it’s a small price to pay for no fleas. Herbal flea treatments might appear to be more dog-friendly but how effective the work is rarely backed up by evidence.”

That’s the conclusion to what I discovered after talking with people, and I am sure you will agree, a lot of it does make sense. I also decided to do more online research and answer some questions which are very closely related.

Can dogs have a reaction to flea treatment?

They certainly can, and in very extreme cases it could even be fatal. On the website they have an entire page dedicated to flea and tick medicine poisoning in dogs (read it here). In fact, there has been some research in the news about flea collars being toxic. Read it before you buy.

The article goes into great detail about pyrethrin and pyrethroid poisoning. These are insecticides used in some dog flea treatments and have been known to cause bad reactions in a small number of dogs.

Whilst bad reactions are rare, it’s worth considering if your dog is acting weird after being given their flea medicine. Here’s what could happen:

  • Allergic reactions: including itching, hives, shock, respiratory problems, and (very rarely) death.
  • Mild reactions: including excessive drooling, paw flicking, ear twitching, mild depression, vomiting, diarrhea.
  • Moderate to serious reactions: including protracted vomiting, diarrhea, depression, lack of co-ordination, and muscle tremors.

In addition to this, I also found some startling information on flea and tick treatment product recalls on the Consumer Affairs website. You can read some guidance on there on how best to use a flea treatment on your dog, whilst exercising extreme caution.

Handy Hint: You should not use commercial flea treatment on newborn puppies, instead follow these easy to understand steps.

Can flea treatment make a dog tired?

Lethargy is another symptom often described by dog owners when the topic of weird behavior comes up with flea treatments.

Whilst I am not a vet and so cannot advise on what to do, if my dog was showing tiredness symptoms after taking flea medicine, I would be very concerned and would seek professional advice.


I opened up this article by describing my own dog’s reaction to flea treatment and how he would act weird. Well, I actually ended up taking him to the vet, and the vet did a little test on Claude using water in a pipette.

He dropped a couple of drops between Claude’s shoulder blades, and he exhibited the same strange behavior. The conclusion was that his weird reaction is simply because the act of applying a topical flea treatment just feels odd to him.

There has been no evidence of burning, and so we are going to stick with the flea treatment for now, on advice of our own vet.

And you should do the same; if you are concerned about your dog’s weird reaction after having his flea medicine, you just don’t know how serious it could be – so please do consult with your vet to rule out anything serious.

Hopefully it’s just your dog being funny, but you never can be too sure.

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Talking of weird, here are some other odd things that dogs do, and the reasons for it!

Marc Aaron

I write about the things we've learned about owning dogs, the adventures we have, and any advice and tips we've picked up along the way.

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