Home /

Dogs / Health

/ Dog Acting Strange After Flea and Tick Treatment

Dog Acting Strange After Flea and Tick Treatment

Dogs can behave strangely after applying flea and tick treatment because they are allergic or have become intoxicated with one of the substances in the product. Products for treating fleas and ticks in dogs are generally safe. They rarely cause allergic reactions unless the dog is sensitive. Intoxication occurs after ingestion of the product.

We love our pets, and we will do anything for them. When they become infested with fleas and ticks, we never think our dogs can be allergic to one of the antiparasitic substances.

Allergy to antiparasitics usually occurs when you have a sensitive dog. Maybe it’s a puppy, and it is its first flea and tick treatment, and you had no way of knowing that can happen. 

Or maybe you changed the product recently. 

In any case, the allergy can be treated quickly by a vet without leaving any damage to your pet. 

There are many types of antiparasitics for pets to choose from if your dog is sensitive to one of them.

Intoxication from antiparasitic products can occur if your dog has ingested the active ingredient. If you do not intervene in time, your pet may die.

In this article, you will find out if flea and tick treatment is toxic to dogs, why dogs react strangely after this treatment, what the side effects of flea and tick treatment in dogs are, and how to treat flea and tick treatment toxicity.

Why Is My Dog Acting Strange After Flea Treatment?

Dogs can react strangely after flea and tick treatment for several reasons. If your dog scratches even harder after application, don’t worry. Look out for signs of allergies and intoxication. Contact the vet as soon as possible if this is the case.

One of the most common reasons why a dog behaves strangely after applying flea and tick treatment is that the substances in these products make the fleas hyperactive before they die. 

Your dog’s skin can become more irritated and start to itch, making your pet behave strangely.

In rare cases, this weird behavior can occur due to stress or anxiety. Some dogs associate the application of antiparasitic products with a stressful event, such as going to the vet (if the product was first applied there).

Other possible explanations include:

  • The manufacturer has replaced old ingredients with new ones
  • The product has expired
  • You used a low-quality product
  • The product has a higher concentration than necessary for the size of your dog

Most dogs handle topical antiparasitics well and do not react strangely. 

These products are safe to use and recommended by many veterinarians. There are exceptions when there has been a mistake in administration or if a dog is sensitive to the active substance.

Spot-on pipettes are the most popular antiparasitic products that can make a dog behave strangely. These are also the most used products because they are efficient and affordable.

The most severe reasons why a dog behaves strangely after the treatment for fleas and ticks are

  • Allergies
  • Skin lesions
  • Intoxication


Dogs can be allergic to almost anything, from foods, cleaning products, and plants to drugs or antiparasitic products.

You have no way of knowing if your dog is allergic to a certain substance or ingredient until it tries it. This can also be the case with antiparasitic substances.

If this is the first time you apply a particular antiparasitic product to your do, watch for strange behaviors. It can be allergic to one or more substances from the product.

Related: Flea Bites on Dogs: Identification & Symptoms

Tick Bite Diseases in Dogs

Skin lesions

If your dog has skin lesions in the area where you apply the antiparasitic product, that region may sting and itch. In more severe cases, the substance can enter the bloodstream and cause intoxication.


If you apply antiparasitics, such as spot-on pipettes, in an inappropriate area, your dog can ingest the product and become intoxicated.

Spot-on pipettes have to be applied in areas where your dog cannot lick the substance. The best areas to apply spot-on pipettes are on the neck between the shoulder blades. For large breeds, they can also be applied to the base of the tail.

The same thing can happen with antiparasitic collars. If the collar is too loose on your dog’s neck, your pet can reach it and chew on it.

Intoxication can also occur when you use the wrong product, not suited for your dog’s weight. If the product you bought has a higher concentration than your dog needs for its weight, the whole amount will absorb into the skin, intoxicating your pet.

Related: Flea Collar Poisoning in Dogs

Tick-Borne Diseases in Dogs

Is Flea and Tick Medicine Toxic for Dogs?

Flea and tick medicines are usually safe for dogs. There is a wide variety of antiparasitic products on the market, and not all of them make dogs sick. Many veterinarians recommend using antiparasitics to prevent ticks and fleas on dogs. 

The antiparasitic products found on the market are numerous and include:

  • Spot-on pipettes
  • Collars
  • Sprays
  • Chewable tablets
  • Powders
  • Shampoos

These products are administered depending on the weight and age of your pet. Some have an effect of up to a few months, while others only for a few weeks. 

The exception is the antiparasitic shampoo, which is effective in removing fleas when you bathe your dog. Although many manufacturers promise that it can also prevent fleas and ticks, antiparasitic shampoo is not effective in this regard.

The most popular antiparasitics are spot-on pipettes. These are also the cause of most cases of intoxication because they are the most used product.

For dogs sensitive to pipettes, collars, powders, or sprays are recommended antiparasitic chewable tablets, which are well tolerated by pets. Chewable tablets can cause allergies and dermatitis in rare cases.[1]

Your dog may behave strangely after applying the flea and tick treatment. Not because it is a toxic product but because of other reasons:

  • Your dog is allergic to one of the substances
  • The product was applied to a wound
  • Your dog ingested the product
  • An inappropriate product was used for the dog’s weight
Is Flea and Tick Medicine Toxic for Dogs

What Are the Side Effects of Flea and Tick Treatment in Dogs?

Side effects of flea and tick treatments vary depending on how your dog reacts to a particular product. If your dog is allergic to one of the substances, it can cause itching, redness, or hair loss. If your pet becomes intoxicated by a product, it may show neurological and digestive symptoms and eventually die.

Antiparasitic products are normally considered safe and should have no adverse effects. Some dogs can experience minor allergic reactions at the site of application, while others can have generalized allergic reactions.

In the case of ingestion of topical antiparasitic substances, the severity of the symptoms of intoxication depends on the amount ingested.

Allergy vs. Intoxication

The immune system can respond to certain substances (which are considered allergens) in a way that is harmful to the body.

An organism’s allergic responses differ in three ways from toxic responses[2]:

  1. It does not appear during the first exposure to an allergen – there are rare occasions when the allergy can occur from the first try.
  2. Allergy is specific to both, the substance that causes the allergy and the individual.
  3. The amount of substance needed to cause an allergy is less than the amount for a toxic response.[3]

If your dog is allergic to flea and tick treatment, it can develop one or more of the following symptoms:

  • Itching
  • Scratching all over its body
  • Overgrooming
  • Redness of the skin, especially in the area where the product was applied
  • Watery eyes
  • Sneeze
  • Cough
  • Respiratory problems

Related: Flea Bite Pet Allergies

What Is Flea Allergy Dermatitis
Image Source

On the other hand, if your dog ingested the product, besides its strange behavior, you may notice:

  • Neurologic symptoms: Incoordination, tremors, seizures, light and noise sensitivity, abnormal pupil dilation
  • Digestive disorders: Vomiting, diarrhea, excessive drooling
  • Respiratory problems: Asthma, difficulty breathing, wheezing, short or fast breathing
  • Fever or hypothermia
  • Itchiness
  • Red skin or rash
  • Hyperactivity or nervousness
  • Fatigue
  • Excessive urination or loss of bladder control

How to Treat Flea Medicine Toxicity in Dogs?

Contact your veterinarian at the first strange behavior you notice in your dog, after applying the antiparasitic product. Remain calm, and don’t wait for the condition to pass because you don’t know what you are dealing with. You risk making your pet’s condition worse.

If you think your dog is behaving strangely after applying the flea and tick treatment, contact your veterinarian immediately. Only they can make a correct diagnosis and be able to treat your dog. 

A vet can’t always save a dog’s life. It depends on the time that has passed since you used the product and the amount applied (in case of inappropriate usage of products) or ingested.

Here are some things you can do to help with your dog’s recovery.

Do not panic

Panic can cloud your judgment and make you take the wrong decisions. Also, your dog can feel your stress and become more agitated.

Do not give your dog milk or oil

Many say it is good to give dogs milk or oil when they become intoxicated. Do not listen to them. Milk or oil can make your dog’s situation worse. Many pets are also lactose intolerant, and milk can cause digestive problems.[4]

Bring the product package to the vet

If you threw away the package, try to remember the product’s name. It is necessary for the veterinarian to figure out what the active substance of the product is to administer the appropriate treatment.

What Not to Do if a Dog Acts Strange After Flea and Tick Treatment

Many times when we want to do good, we risk doing more harm. In order to avoid worsening your dog’s situation, you should not

  1. Underestimate the severity of the problem. Many dog owners choose to wait for the situation to go away on its own, but in fact, they have done more harm.
  2. Cause vomiting. Some substances can be caustic and can burn your dog’s digestive tract. Induce vomit if your veterinarian tells you to.
  3. Never use the same product again.


Products used as anti-flea and -tick treatments are generally safe to use in dogs. In rare cases, if your dog is sensitive, they can cause allergies, which are easy to treat.

There are also unwanted situations in which your dog has ingested the product or you used an inappropriate product. In these cases, your dog may become intoxicated.

Flea and tick toxicity has a variety of symptoms, depending on the amount of product ingested or applied. In some cases, your dog can die if you don’t act immediately.

Always follow the instructions on the label to reduce the risk of poisoning, and use products that are appropriate for your dog’s weight.


Can Flea and Tick Treatment Make a Dog Sick?

Flea and tick treatment for dogs is usually safe, but there are cases when it can make a pet sick. If the product was ingested or the amount you applied to its skin was not suited for the dog’s weight, it can become intoxicated. Some dogs are more sensitive to the active ingredients in a product and can develop an allergic reaction.

Why Is My Dog Vomiting After Flea Treatment?

Vomiting after flea treatment can happen as a result of ingesting the product. Besides vomiting, you can notice other symptoms in your dog, such as panting, coughing, incoordination, seizures, and more.

Can You Overdose on Flea Treatment?

Yes, you can overdose on flea treatment if you use the wrong product. Flea and tick products are specially designed for weight groups. It is not recommended to use a flea product suited for medium dogs on a small breed dog as it can become intoxicated.

About Iulia Mihai (DVM)

Dr. Iulia is a certified veterinarian with more than 10 years of experience in the field. With extensive knowledge of diet, care, and medication, she helps Misfit Animals provide readers with accurate knowledge on technical topics.

Looking for something?

Try searching our website!