Complete Guide | Dog & Cat Flea, Tick, Heartworm Medication Side Effects

Reference guide to side effects of common conventional medications recommended and sold by the veterinarian industry to 'prevent' and 'treat' dogs and cats for e.g., fleas, ticks and tick borne diseases, heartworm, intestinal parasites, lungworm, mites, etc. There is a better option...

⭑ 12 min read

In this article:

1. Introduction
2. A Pervasive Threat to Health
3. Did Your Veterinarian Inform You?
4. Complete Guide to Side Effects and Risks
1. But How Bad Can the Side Effects Really Be?
2. Amitraz (Amitraz, Vermitraz, etc.) 
3. Diflubenzuron (Vectra, etc.)
4. Dinotefuran (Simple Guard, Vectra) 
5. Fenbendazole (Pancure, etc.)
6. Fipronil (Frontline, Proline, etc.) 
7. Fluralaner (Bravecto, Vetecto, etc.) 
8. Imidacloprid (Advocate, K9 Advantix, Seresto, etc.)
9. Ivermectin (Heartgard, Tri Heart Plus, etc.)
10. Milbemycin Oxime (Interceptor, Nexgard, etc.)
11. Nitenpyram (Capstar, etc.)
12. Praziquantel (Interceptor Plus, etc.)
13. Pyrantel Pamoate (Heartgard, Simparica Trio, etc.)
14. Pyrethins (dips, shampoo, spot on, sprays)
15. Pyrethroids (K9 Advantix II, Spot on products)
16. Selemectin (Revolution, etc.)
17. Spinosad (Comfortis, Trifexis)
5. The Truth About Heartworm, Preventative Medications v.s Natural Prevention
6. Fleas and Flea Infestations, Natural Prevention and Treatment
7. Ticks, Natural Prevention 
8. Intestinal Parasites, Natural Prevention and Treatments
9. The Best Prevention and Treatment

1.0 Introduction 

 

Are you currently using conventional flea, tick, heartworm and worming medications for your dog and cat? Or you're thinking of using conventional medications pills or chewables (e.g. Pancur, Bravecto, Heartgard etc.), spot on, dip, spray, flea bombs or flea collars.

 

This article is a reference guide to the adverse side effects of common conventional medications recommended and sold by the veterinarian industry to 'prevent' and 'treat' dogs and cats for:

1. Fleas
2. Heartworm
3. Intestinal parasites (e.g. giardia, hookworm, tapeworm, whipworm, etc.)
4. Lice
5. Lungworm
6. Mites
7. Mosquitoes
8. Ticks
9. etc. 

Insect and parasite conventional medications (preventatives and treatments) are popular and may seem convenient, however the active ingredients are health damaging.

 

When a beloved dog or cat becomes seriously ill (after use of conventional preventatives) the stress and grief is anything but convenient.

 

If your veterinarian claims to be holistic:

• But is prescribing conventional flea medications for your dog or cat;
• Your veterinarian is an integrative veterinarian, or conventional veterinarian; not an holistic veterinarian.

The pet and veterinary industry often misuse the term 'holistic' in an effort to deceive potential clients/patients and charge increased fees for products and services.

 

This article will help you better understand the significant negative impact of popular conventional preventatives and treatments. 

 

There is a better option. A layered natural approach tailored to suit your dog and cat:

• Provides the best defence against insects, parasites and insect, parasite-borne disease.
• Supports overall health, unlike the conventional approach which is health deteriorating. 

 

2.0 A Pervasive Threat to Health

 

Conventional insect, parasite medications (preventatives and treatments) are marketed as 'safe' and necessary. However, these products cause significant harm.

 

Sometimes the harm is immediate and obvious. 

1. Serious,
2. Life-threatening, or;
3. Fatal.

However, for most dogs and cats the harm is insidious. The toxic burden erodes your animal's health, eventually causing serious health issues. You can avoid this heart-breaking outcome.

 

A natural approach to insect and parasite prevention and treatment is effective and supports overall health.

 

3.0 Did Your Veterinarian Inform You?  

Conventional flea, tick, heartworm, and intestinal parasite medications are not a solution, they are part of the problem.

 

Made with synthetic chemical pesticides are so toxic the labels on the products warn 'do not touch or administer' with your bare hands.

 

Why?

 

Because the active ingredients are harmful to:

• Blood health
• Gut biome 
• Immune system function
• Kidney function
• Liver function
• Neurological function
• Thyroid function 

The overall effect results in acute damage and chronic disease, including cancer.

 

Just one use can cause damage to your dog and cats immediate and long-term health health. Risk of harm to your dog's and cat's health increases with repeated and long-term use.

 

4.0 Complete Guide to Side Effects and Risks

of conventional insect, parasite prevention and treatment products

 

The list below provides examples of common synthetic-chemical pesticide medications used to prevent insect and parasite infestations for dogs and cats. Uses, side effects and risks are listed under each product. 

 

Some products include two or more of the insecticides listed below. 

For example:

• Heartgard Plus - active ingredients are Ivermectin and Pyrantel.
• Interceptor -  active ingredients are Praziquantel

4.1 But How Bad Can the Side Effects Really Be?

The short answer is, the side effects are: 

1. Life altering.
2. Quality of life damaging.
3. Deathly. 

According to the American Veterinary Medical Association: 

"65% of adverse drug reactions and 48% of all reported deaths resulting from drug reactions are caused by heartworm preventatives."

 

According to the EPA:

 

In 2022, using the freedom of information act, the Centre for Biological Diversity worked tirelessly to obtain data from the EPA regarding the Seresto Collar. An important highlight from the report reveals the devastating truth.

 

"The new EPA data reveals that there has been an average of 25 dog and cat injury reports per day since the collars went on the market in March 2012. An average of 21 pet deaths linked to the collars have been reported each month."

 

Read the Centre for Biological Diversity's report from November 2022, and the EPA's data as released through the freedom of information act here.

 

Now let's take a look at the list of common conventional flea, tick, heartworm, lungworm, intestinal worming products and their adverse side effects.

 

4.2 Amitraz 

 

Amitraz is an acaricide, insecticide, active ingredient in e.g:

• Amitick
• Amitraz
• Proventic
• TrazCare
• Vermitraz

used to repel and kill: 

• fleas, lice, mites and mange, scabies, ticks

side effects on dogs and cats (partial list)

• eye issues - conjunctivitis, dilation of pupils
• fur loss  
• skin issues, e.g. irritation, itchiness, rashes, skin diseases 
• gastrointestinal issues
• anorexia 
• high blood sugar (hypoglycemia)
• hyper-salivation
• kidney damage
• liver damage 
• lethargy
• low blood pressure (hypo-tension),
• low body temperature (hypothermia) 
• respiratory depression
• ataxia
• bradycardia (slow heart beat)
• sedation
• cancer, increased risk
• central nervous system depression
• convulsions, seizures
• death

dogs and cats most at risk for adverse side effects: 

• puppies and kittens under 12 weeks of age
• senior
• debilitated, ill
• medicated
• pregnant or nursing
• sensitive to pesticides

 

4.3 Diflubenzuron, Fenoxycarb,  Lufenuron, Methoprene, Pyriproxyfen (e.g. Frontline Plus, Sentinel)  

Insect growth regulators (IGEs), active ingredient in e.g:

• Fiprofort Plus
• Frontline Plus
• Nextstar
• Preventic
• Program
• Sentinel Spectrum
• Diflubenzuron
• Fenoxycarb
• Lufenuron
• Methoprene
• Pyriproxyfen

used to repel and kill: 

• fleas, heartworm, intestinal worms, lice, ticks.

side effects on dogs and cats (partial list): 

• abdominal pain
• bone malformation
• cancer, increased risk
• diarrhea
• decreased appetite 
• DNA damage 
• growth malformation  
• hematoma
• hyper-salivation 
• skin issues, e.g. itching, redness, hives, severe reactions.
• vomiting 
• sedation
• kidney damage 
• lethargy
• liver damage 
• anorexia 
• difficulty breathing 
• damage to hemoglobin 
• tremors
• seizures
• skeletal malformation 
• death  

dogs and cats most at risk for adverse side effects:  

• young (puppies, kittens)
• senior
• debilitated, ill
• medicated
• pregnant or nursing dog
• sensitive to pesticides

4.4 Dinotefuran (e.g. Vectra) 

Dinotefuran is a neo-nicotinoid insecticide, active ingredient in e.g:

• Dinotefuran
• Simple Guard
• Vectra

used to repel and kill: 

• fleas

side effects on dogs and cats, partial list: 

• cancer, increased risk 
• diarrhea
• hyper-salivation 
• skin issues, e.g. itching, redness, pustules, etc.
• vomiting 
• tremors
• seizures
• death  

dogs and cats most at risk for adverse side effects:  

• senior
• debilitated, ill
• medicated
• pregnant or nursing dog
• sensitive to pesticides 

 

4.5 Fenbendazole (e.g. Pancure)

Fenbendazole is a neonicotinoid pesticide, active ingredient in e.g:

• Fenbendazole
• Fencur 
• Pancure
• Panacure
• Pancur C
• Safeguard

used to repel and kill: 

• intestinal parasites, lungworm

side effects on dogs and cats (partial list): 

• abdominal pain
• cancer, increased risk 
• diarrhea
• decreased appetite 
• hyper-salivation 
• vomiting 
• dehydration 
• lethargy
• depression 
• anorexia 
• gut damage 
• fur loss
• skin issues, itchiness, redness, blistering, hives, lesions 
• joint pain 
• bone marrow suppression
• low red blood cells, low white blood cells, low platelets 
• tumors
• liver damage 
• urinary issues 
• swelling
• fever  
• convulsions 
• tremors
• shock
• seizures

dogs and cats most at risk for adverse side effects:  

• debilitated, ill
• medicated 
• sensitive to pesticides

 

4.6 Fipronil (e.g. Frontline)

Fipronil (e.g. Frontline) is a phenylprazole insecticide, active ingredient in e.g:

• Fiprofort Plus
• Fipronil
• Fronil
• Frontline
• Neoveon Plus
• Proline

used to repel and kill: 

• fleas, ticks

side effects on dogs and cats (partial list): 

• agitation
• aggression
• hyper activity
• hypo activity 
• cancer, increased risk
• dizziness 
• nausea  
• vomiting
• skin issues - itching, redness, etc.
• weakness 
• vocalization 
• ataxia 
• convulsions 
• tremors 
• seizures 
• death 

dogs and cats most at risk for adverse side effects:  

• puppies and kittens under 8 weeks of age
• seniors
• medicated
• debilitated, sick 
• sensitive to pesticides


4.7 Fluralaner (e.g. Bravecto) 

Fluralaner is an isoxazoline insecticide, active ingredient in e.g:

• Bravecto
• Fluralaner 
• LanerWIN
• Lucpets
• PearlZie
• Vetecto

used to repel and kill: 

• fleas, mites, ticks.

side effects on dogs and cats (partial list): 

• cancer, increased risk
• diarrhea
• decreased appetite 
• hyper-salivation 
• skin issues, e.g. itching, redness, etc.
• vomiting 
• dehydration 
• lethargy
• anorexia 
• tremors
• ataxia 
• seizures
• death  

dogs and cats most at risk for adverse side effects:  

• senior
• debilitated, ill
• medicated
• pregnant or nursing dog
• sensitive to pesticides 

4.8 Imidacloprid (e.g. Advocate, K9 Advantix, Seresto)

Imidacoprid is a systematic insecticide, active ingredient in e.g:

• Advantage II
• Advantage Multi
• Advantus
• Advocate
• BanFlea II
• Barrier
• Imitrim
• Imidacloprid
• K9 Advantix
• Neovet 
• Parasedge Multi
• Sargents
• Seresto Collars

used to repel and kill: 

• fleas, heartworm, lungworm, ticks.

side effects on dogs and cats (partial list): 

• cancer, increased risk 
• diarrhea
• decreased appetite 
• hyper-salivation 
• skin issues, e.g. itching, redness, etc.
• vomiting 
• dehydration 
• lethargy 
• gut damage 
• anorexia 
• difficulty breathing 
• muscle weakness 
• miscarriage
• skeletal deformities 
• tremors
• ataxia 
• shock 
• seizures
• death  

dogs and cats most at risk for adverse side effects:  

• puppies and kittens under 7 weeks of age
• dogs and cats under 3 lbs of body weight
• those with low body temperatures 
• dogs and cats with mutation of the MDR1 gene mutation (defective P-glycoproteins).
• dogs, e.g: Australian shepherds, border collies, German shepherds, sheep dogs, merle pomeranians, long-hair whippets, Shetland sheep dogs.
• cats, e.g: Balinese, main coon, ragdoll, Russian blue, Siamese, Turkish angora.
• debilitated, ill
• medicated 
• pregnant and nursing
• sensitive to pesticides

4.9 Ivermectin (e.g. Heartgard Plus, Iverheart)

Ivermectin is an antiparasitic, active ingredient in e.g:

• Heartgard
• Heartgard Plus
• Heartshade
• Imectro
• Iverheart
• Iverhelm
• Ivermectin
• Ivomec
• Pet Trust
• StrongHeart
• Tri Heart Plus

used to repel and kill: 

• heartworm, lungworm

side effects on dogs and cats (partial list): 

• cancer, increased risk 
• diarrhea
• decreased appetite 
• hyper-salivation 
• vomiting 
• lethargy  
• liver and kidney damage 
• disorientation 
• depression 
• anorexia 
• difficulty breathing 
• bradycardia (slow heart beat)
• dilated pupils 
• blindness
• stumbling, in-coordination 
• ataxia 
• tremors
• seizures
• coma 
• death  

dogs and cats most at risk for adverse side effects:  

• dogs and cats with mutation of the MDR1 gene mutation (defective P-glycoproteins).
• dogs, e.g: Australian shepherds, border collies, German shepherds, sheep dogs, merle pomeranians, long-hair whippets, Shetland sheep dogs.
• cats, e.g: Balinese, main coon, ragdoll, Russian blue, Siamese, Turkish angora.
• debilitated, ill
• pregnant and nursing 
• sensitive to pesticides

 

4.10 Milbemycin Oxime (e.g. Interceptor, Nexgard)

Milbemycin ozime is an antiparasitic, active ingredient in e.g:

• Interceptor
• Interceptor Plus
• MilbeGuard
• Milbemax
• Milbemycin
• Milprazon
• Nexgard
• ProVectra
• Sentinal Spectra
• TriFlexis

used to repel and kill: 

• heartworm, intestinal parasites

side effects on dogs and cats, partial list: 

• cancer, increased risk
• diarrhea
• decreased appetite 
• hyper-salivation 
• vomiting 
• dehydration 
• liver and kidney damage 
• lethargy
• depression 
• anorexia 
• skin issues, itchiness, redness 
• fever 
• tremors
• stupor 
• ataxia 
• seizures
• coma 
• death  

dogs and cats most at risk for adverse side effects:  

• dogs and cats with mutation of the MDR1 gene mutation (defective P-glycoproteins).
• dogs, e.g: Australian shepherds, border collies, German shepherds, sheep dogs, merle pomeranians, long-hair whippets, Shetland sheep dogs.
• cats, e.g: Balinese, main coon, ragdoll, Russian blue, Siamese, Turkish angora.
• debilitated, ill
• medicated 
• pregnant and nursing
• those with pre existing seizure conditions 
• sensitive to pesticide

 

4.11 Nitenpyram (e.g. Capstar)

Nitenpyram is a neonicotinoid pesticide, active ingredient in e.g:

• Bestgard
• CapAction
• Capstar
• Fastcaps
• Flea Shield Max
• Nitenpyram

used to repel and kill: 

• blow flies, fleas, heartworm, intestinal parasites, maggots

side effects on dogs and cats (partial) list: 

• anxiety 
• cancer, increased risk
• diarrhea
• decreased appetite 
• hyper-salivation 
• vomiting 
• dehydration  
• liver and kidney damage 
• lethargy
• depression 
• hyperactivity 
• vocalization 
• anorexia 
• gut damage 
• skin issues, itchiness, redness 
• fever 
• tremors
• stupor 
• ataxia 
• seizures
• coma 
• death  

dogs and cats most at risk for adverse side effects:  

• dogs and cats with mutation of the MDR1 gene mutation (defective P-glycoproteins).
• dogs, e.g: Australian shepherds, border collies, German shepherds, sheep dogs, merle pomeranians, long-hair whippets, Shetland sheep dogs.
• cats, e.g: Balinese, main coon, ragdoll, Russian blue, Siamese, Turkish angora.
• debilitated, ill
• medicated 
• pregnant and nursing
• those with pre-existing seizure conditions 
• sensitive to pesticide

 

4.12 Pyrantel Pamoate (e.g. Heartgard. Simparica Trio, Strongid P)

Pyrantel pamoate is a pesticide, active ingredient in e.g:

• Heartgard
• FepraCare
• Nemex
• Pyrantel
• Praziguard Plus
• Simparica Trio
• Strongid P
• Sure Shot

used to repel and kill: 

• intestinal parasites, lungworm, heartworm

side effects on dogs and cats (partial list): 

• abdominal pain
• cancer, increased risk
• diarrhea
• decreased appetite 
• hyper-salivation 
• vomiting 
• dehydration 
• liver and kidney damage 
• lethargy
• loss of balance 
• depression 
• anorexia 
• gut damage 
• skin issues, itchiness, redness, blistering, hives, lesions  
• facial swelling
• pale gums
• cold limbs  
• convulsions 
• tremors
• shock
• seizures
• coma
• death 

dogs and cats most at risk for adverse side effects:  

• debilitated, ill
• medicated 
• sensitive to pesticides

4.13 Pyrethrins 

Pyrethins are an insecticide, active ingredient in e.g:

• flea and tick dips
• flea and tick shampoo
• spot on treatments
• flea and tick sprays 

used to repel and kill: 

• fleas, mosquitoes, ticks and other insects

side effects on dogs and cats (partial list): 

• abdominal pain
• cancer, increased risk
• diarrhea
• decreased appetite 
• hyper-salivation 
• vomiting 
• dehydration 
• liver and kidney damage 
• lethargy
• anorexia 
• gut damage 
• skin issues, itchiness, redness, blistering, hives, lesions  
• pale gums
• convulsions 
• tremors
• shock
• seizures
• coma
• death 

dogs and cats most at risk for adverse side effects:  

• puppies and kittens under 7 weeks of age
• debilitated, ill
• medicated 
• pregnant and nursing dogs and cats 
• sensitive to pesticides

4.14 Pyrethroids 

Pyrethroids are an insecticide, active ingredient in e.g:

• K9 Advantix II
• Pyrethroid Spot On products
• Vectra 3D 

used to repel and kill: 

• fleas, mosquitoes, ticks and other insects

side effects on dogs and cats (partial list): 

• abdominal pain
• cancer, increased risk
• diarrhea
• decreased appetite 
• hyper-salivation 
• vomiting 
• dehydration 
• lethargy
• anorexia 
• gut damage 
• skin issues, itchiness, redness, blistering, hives, lesions  
• pale gums
• respiratory distress
• DNA damage
• heart damage 
• kidney damage
• liver damage 
• convulsions 
• tremors
• shock
• seizures
• coma
• death 

dogs and cats most at risk for adverse side effects:  

• puppies and kittens under 7 weeks of age
• debilitated, ill
• medicated 
• pregnant and nursing dogs and cats 
• sensitive to pesticide

4.15 Praziquantel (e.g. Drontal, Interceptor Plus)

Praziquantel is an anthelmipesticide, active ingredient in e.g:

• Droncit
• Drontal Plus
• Interceptor Plus
• FentelCare
• Prazital
• Prazitabs
• PrazyTox
• Sentinal Spectrum

used to repel and kill: 

• intestinal parasites, lungworm

side effects on dogs and cats (partial list): 

• abdominal pain
•  cancer, increased risk
• diarrhea
• decreased appetite 
• hyper-salivation 
• vomiting 
• dehydration 
• lethargy
• depression 
• anorexia 
• gut damage 
• fur loss
• kidney damage
• liver damage 
• skin issues, itchiness, redness, blistering, hives, lesions 
• joint pain 
• bone marrow suppression
• low red blood cells, low white blood cells, low platelets 
• tumors
• liver damage 
• urinary issues 
• swelling
• fever  
• convulsions 
• tremors
• shock
• seizures

dogs and cats most at risk for adverse side effects:  

• puppies and kittens under 4 weeks of age
• debilitated, ill
• pre existing kidney issues 
• pre existing liver issues 
• medicated 
• sensitive to pesticides

 

4.16 Selemectin (e.g. Revolution, Senergy) 

Selemectin is a parasiticide, active ingredient in e.g: 

• Evicto 
• Revolt 
• Revolution 
• Selarid 
• Senergy

used to repel and kill: 

• fleas, heartworm, intestinal parasites, mange, mites, ticks.

side effects on dogs and cats (partial list): 

• cancer, increased risk
• hair loss
• skin issues, and burns
• gut damage
• immune system damage 
• blindness
• kidney damage
• liver damage 
• ataxia
• seizures
• coma
• death

dogs and cats most at risk for adverse side effects:  

• all dogs and cats.

4.17 Spinosad

Spinosad is an insecticide, active ingredient in e.g:

• Comfortis
• Trifexis

used to repel and kill: 

• fleas

side effects on dogs and cats (partial list):

• cancer, increased risk
• loss of appetite
• diarrhea
• vomiting
• gut damage
• kidney damage
• liver damage 
• itching
• ataxia, seizures, death

dogs and cats most at risk for adverse side effects:   

• pregnant and nursing animals
• animals under 14 weeks of age
• animals with seizure conditions
• all dogs and cats

 

5.0 The Truth About Heartworm, Conventional Heartworm Preventatives vs Natural Prevention

 

Learn more about heartworm:

1. Find out if you're really in a high-risk zone or if the veterinary industry is pressuring you for profit at the expense of your dog's health and well-being.
2. Asses the real risks for your dog's personal situation.
3. Find out how heartworm infestations occur.
4. Learn more about the dangers of conventional 'preventatives' e.g. Heartgard Plus, etc. 
5. Learn about a natural approach to heartworm prevention. 

Go to this article.

 

 

6.0 Fleas and Flea Infestations, Natural Prevention and Treatment 

Learn more about fleas and flea infestations:

1. What makes some dogs and cats highly vulnerable to fleas and flea infestations.  
2. Dietary support.
3. Avoid these common mistakes.  
4. Natural prevention and treatments.

Go to this article.

 

7.0 Ticks, Natural Prevention 

Your dog's best defence against ticks and tick borne disease is a layered, natural approach tailored to suit your companion animal's individual situation. Learn more:

 

Go to this article.

 

 

8.0 Intestinal Parasites, Natural Prevention and Treatment 

Intestinal parasites (e.g. hookworm, round worms, tapeworm, etc.) can be successfully prevented and treated with a properly designed natural protocol. Learn more about natural worming and prevention for your dog and cat:

 

Go to this article.

 

 

9.0 The Best Prevention and Treatment Protocol 

 

The best natural, holistic treatment protocol depends on your individual dog's and cat's overall circumstances.

 

If your dog or cat has chronic health issues from:

• Exposure to conventional preventatives, (e.g. gut damage, immune system damage,  endocrine issues, kidney or liver damage, seizures, etc) or;
• Insect/parasite borne infections (e.g. tick borne diseases, intestinal parasite infestations, fleas, heartworm, lungworm, etc.).

I design comprehensive, natural and effective prevention plans specifically tailored to your dog's or cat's individual situation. 

 

Learn more here. 

 

 

If you don't put your dog or cat on conventional preventatives and treatments and are committed to adopting a natural and holistic approach:

• My holistic wellness services can be engaged to create a comprehensive, natural and effective prevention plan for your dog or cat.

 Learn more here.

 

 

Holistic Diet, Nutrition, Wellness Services Tailored to Your Individual Dog and Cat

For information about my holistic diet, nutrition and wellness services, visit my holistic wellness services page.

Maintain good health | Address acute and chronic health issues | Pre and post surgery support and recovery

My holistic wellness services are available worldwide via video consultation.

🌎 USA | Canada | UK | Europe | Australia | New Zealand | Asia | South and Central America | Africa | UAE

📱FaceTime | Facebook | Microsoft Teams | WhatsApp

To set-up your holistic wellness consultation get in-touch via email, go to my contact me page.

 

Holistic Behavioral Services for Your Dog

For information about my holistic behavioral services, visit my holistic behavioral services page.

For dogs of all ages, sizes and breeds.

My behavioral services are available worldwide via video consultation.

🌎 USA | Canada | UK | Europe | Australia | New Zealand | Asia | South and Central America | Africa | UAE

📱FaceTime | Facebook | Microsoft Teams | WhatsApp

To set-up your holistic behavioral session get in-touch via email, go to my contact me page. 

 

Affiliations to Companies  

✓ None. 

✓ I don't sell food, supplements, or other products.

✓ I'm not aligned with any companies. 

 

Article and graphics by Karen Rosenfeld.