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The Side Effects of Frontline Flea & Tick Prevention

 by simone on 05 Jun 2014 |
35 Comment(s)

Fleas are bad - very bad - and ticks are even worse! Fleas don’t just irritate cats and dogs, driving them barking (or meowing) mad with excessive itching and biting, they also spread diseases which can transmit to people. Ticks, especially the paralysis tick, can be fatal.

Fleas have a four-stage life cycle: adult, egg, larva and pupa. These nasty little parasites bite, feed and breed on your pet. An adult female flea can lay up to 50 eggs per day. Once your pet and home is infested, it is difficult to banish fleas entirely. 

Brown ticks and paralysis ticks are dangerous to pets of all ages. Tick saliva has toxins that are passed on when they suck blood from your pet. These toxins irritate your pet’s skin, cause dermatitis and anaemia and can even lead to paralysis or death. Ticks also carry Lyme disease. Therefore, it is essential that you regularly protect your pet from fleas and ticks. 

Frontline is a very fast acting and effective prevention for fleas, flea eggs and larvae, biting lice and ticks. On fleas, Frontline acts on three important reproductive stages, therefore successfully destroying their lifecycle. The ingredient fipronil affects adult fleas, lice and ticks, and methoprene affects the flea eggs and larvae. Frontline begins woking immediately to attack the parasite’s central nervous system, paralysing then killing them. Frontline can also be used to treat Flea Alergy Dermatitis. 

There are a range of Frontline products suitable for cats and dogs that can be applied either monthly or bi-monthly. The dosage for dogs is dependent on the dog’s weight. The treatment comes in pipettes which is squeezed through your pet’s hair directly onto their skin between the shoulder blades where it can’t be licked. Avoid getting Frontline in your pet’s eyes or allowing them to ingest it. Frontline Plus and >Frontline Combo are different brand names for the same product. 

After 24 hours, Frontline is distributed entirely over your pet’s skin and hair via their oil glands. Once spread, Frontline is water resistant though it is advised that you do not shampoo your pet for 48 hours after treatment. For paralysis tick control, you should continue to carefully check your pet for infestation, particularly during tick season. You may need to apply treatment every two weeks during this time. Refer to instructions on the packaging. 

Side Effects

Frontline is a tested and safe treatment for cats and dogs. When used as directed, dangerous side effects are rare. It is intended for use on kittens and puppies over 8 weeks of age and can be used on pregnant or lactating animals. You will need to talk to your vet prior to use if your pet is on medication, has a weakened immune system, is sick, aged or if you are already using other pesticide.

There may be temporary redness or skin irritation at the site of application for 1-2 days which will cause your pet to itch or scratch. Some lack of appetite and diarrhoea may also occur. Your pet may drool if they lick the treatment before it has dried. If these symptoms persist or worsen, it could be a sign of an allergy so consult your vet. 

Any adverse reactions or side effects using Frontline are usually due to incorrect administration or dosage. However, all pets are individuals and may be hypersensitive or allergic to the ingredients. If you notice any of the following side effects take your pet to the vet immediately: 

  • Swelling particularly of the face, lips and tongue
  • Rash or hives
  • Lethargy
  • Vomiting or severe/lengthy diarrhoea
  • Excessive salivation
  • Uncoordinated movements
  • Seizure 
  • Unresponsiveness or coma

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Peter - Comment
Peter24 Apr 2017Reply
After applying Frontline our cat suddenly behaved strangely as though she was having a fit
Peter - Comment
Peter24 Apr 2017Reply
Our cat reacted after being treated with Frontline. Looked like she was having a stroke or seizure but recovered . Very worrying while it lasted.
Becky - Comment
Becky12 Jul 2017Reply
Frontline is crap, I have treated my dog and cats as I do monthly all of them still have fleas and scratch more then they did before. Also my dog now seems to struggle to jump with his back legs and can no longer get on the sofa or bed.
Lorene  - Comment
Lorene 12 Aug 2017Reply
I use to use Frontline Plus on my cat, but yesterday vet gave me frontline gold. Anyway was in the vet office for 2 hours this morning, as my usually noisy up at 5 AM cat, was hiding under the bed this morning and had vomited during the night. After almost $400 of fluids, anti nausea, and blood panel, she is still not meowing, eating or moving around much. Not applying this stuff ever again.
Betty - Comment
Betty15 Aug 2017Reply
How long after treatment will adverse reaction symptoms appear? I treated my cat who is 12 years old one week ago with Frontline Gold and today she is acting like her back end is out of whack and can hardly walk.
Cindy - Comment
Cindy17 Aug 2017Reply
I was feeding really bad when I finally caught my 3 indoor outdoor ferals to apply the Frontline Plus.All of them cried like it really hurt. They act very tired.I need to do my research
Jo - Comment
Jo23 Aug 2017Reply
I gave my 20 year old cat Frontline after reading the instructions and telling my vet I was doing it. On both occasions he has gone off his food and had diarrhoea which ARE on the list of side effects, but he goes blind for 24 hours about 48 hours after application... this was certainly NOT on the list. It's very scary and distressing but does not last .... be warned everyone!!!
Denise - Comment
Denise08 Nov 2017Reply
it's worked on my boy he looks really relaxed, i gave it to him when i knew he really really needed it ,& only till then . i thought he looked tired, but he really alert i must say i was worried for nothing,
Mary  - Comment
Mary 11 Nov 2017Reply
Call me crazy, but my pets have successively became me I’ll and have a weird eye thing almost exactly one month after using frontline naturals for cats and frontline plus for dogs (cats both have lethargy, and pulled up inner eye lids, bad gas and really grumpy. One is 6-outdoor mostly, one is only 6 months-indoor only. My boxer now had a really irritated eye, possibly from kitten, but also see a hazy spot in eye). we had many skunks around so we had an influx of fleas. I have found eucalyptus they hate. Hate fleas, hate this product, and any like it. Zodiac is pure death.
Mel - Comment
Mel22 Jan 2018Reply
My dog also is reluctant to jump up on my bed or into the car since using frontline plus. She’s very lethargic too. This is very worrying to see other cases. Can you tell me if your dogs recovered ok and how long it took
Tonya - Comment
Tonya28 Jan 2018Reply
I applied the Frontline Plus to my Granddoggie 9 days ago. Yesterday she started presenting with difficulty walking. Today she has to be picked up to go outside to potty. She cannot go up and down any steps. I was glad to find your comments, because I am now almost certain it has made her sick. She also feels very hot and is having rigors We have her on a heating pad and will try bathing her tomorrow.
Tonya  - Comment
Tonya 28 Jan 2018Reply
This is what my Granddoggie is doing!
Ginny Goldberg - Comment
Ginny Goldberg19 Feb 2018Reply
I applied FrontLine Plus to both my dogs. The following day my 6-year old stopped jumping up on the bed or couch. By that night she was having problems walking. By the time I got her to the vet she was paralyzed. I had no choice but to have her euthanized. This was not the first time I've used FrontLine on them and if I had known about these side effects I would NEVER had subjected my furbies to this poison.
Anna - Comment
Anna01 Mar 2018Reply
Feb 26 put frontline on my Burnaby.comefeb 27th she started acting funny wouldn't hardley walk or jump ,took her to the vet dehydrated did blood work found nothing wroung,i called frontline and reported.How long will this take to ware off.I won't use it again !!!! Scared!!!!! Should. I wash her....
Regina P - Comment
Regina P12 Mar 2018Reply
I put frontline on my 10-year-old Chihuahua...Since then, she won’t eat, has diarrhea, walks like she is very uncoordinated, won’t go up and down the stairs, acts like she’s losing her mind. I will never use this product again.
Denice DeMitri - Comment
Denice DeMitri20 Mar 2018Reply
I gave put the Frontline plus on my 11 year old Chi Saturday on Sunday she did nothing but cry she kept twitching and seemed like she was having trouble jumping on furniture, she is fine today. Will never put the Frontline on her again. My 5 year old Chi was fine but she will not get that again either
Mimi - Comment
Mimi07 Apr 2018Reply
We used Frontline on our cat 3 days ago and she started acting odd- hiding, skittish, staggering. She passed away about 20 minutes ago.
LaDonna Wilson - Comment
LaDonna Wilson10 May 2018Reply
I put this Frontline plus on my 11 year old cat 3 day ago and her fur is falling out and after reading this comments I’m starting to get very nervous!! Can anyone tell me how long these symptoms last..
Tonya - Comment
Tonya12 May 2018Reply
i put frontline combo on my longhaired cat bout 10days ago he now has a scab right where i put the spot on he is 11yrs old is acting normally just concerned is this an allegic reaction n if so what could i use instead
Molly - Comment
Molly16 May 2018Reply
My mum put frontline on my back and a week later I have a lump under my skin should I go to the vets
Mel - Comment
Mel20 May 2018Reply
Please everyone as soon as you see symptoms wash your pet in fairy dishwashing liquid or a degreasing dishwashing liquid to remove the frontline from their oil glands. Wash them several times to make sure you get it all off them. There’s some very sad stories above indeed ????????
Nancy Kolosso - Comment
Nancy Kolosso20 May 2018Reply
We have a small claims case against Merial, the makers of this poison. Please go to our website at to join us (no need to testify) or for information. Please sign our petition. Anyone can sign it. That link is Please pass it on to your family and friends. We need everyone's help. Thank you!!
Eleanor - Comment
Eleanor24 May 2018Reply
Sad stories indeed. I’ve had the same experience with hartguard for heart worms. My little dog began to have seizure-like symptoms which worsened over the months. Finally after the last dose I gave her she couldn’t even stand within two hours. The vet never mentioned it might be the ivermectin. He still refuses to believe that was the cause. After I finally researched the product I found out the truth. All of these products contain neuro toxins that are supposed to kill the parasites and not cross the blood brain barrier of the animal. But with some dogs and especially sickly or old ones, it does! My dog had what they called ataxia. Staggering, shaking, seizure-like symptoms, eyes flitting back and forth rapidly, until finally after the last time we thought we’d have to put her to sleep. But we didn’t, and it took 6 weeks in a dog baby buggy and hand feeding because she was blind and couldn’t hold her jerking head still enough to eat on her own. It ends well though. I quit giving it to her and now I use Wondercide. The one I use has cedar oil and hydrated silica, which is like diatomaceous earth. It kills the fleas! Really. Has to be applied quite often if it’s to repel mosquitos too, but in winter a couple of times a week handles fleas. The fleas just sort of dissolve. The little dog recovered very well after that and loved having the cedar smell on her. Not all of them like it that much but the point is, it will do no harm and it works if you’re willing to go to the trouble. I never want to poison my sweet dogs again, so I do.
Eleanor - Comment
Eleanor24 May 2018Reply
I forgot to mention that I have used it on my cat too with success. She’s a rather skittish cat too, but got to where she loved when I’d spray the Wondercide on my hand and rub it all over her. The smell of the cedar didn’t seem to bother her and it didn’t affect her badly in any way. I know cats are different from dogs, but she did fine with it. The only problem is because of the cedar oil, it made her fur clump and I had to brush her frequently to keep that from happening. Go to the product’s website and you’ll find all the info you need. They have products to spray in your house or yard also. Been using it for a year now with success and no more sick animals
Margie Rosenblum - Comment
Margie Rosenblum19 Jun 2018Reply
My dog has the same symptom. Can't jump on her bed.
Chevy - Comment
Chevy05 Jul 2018Reply
We used Frontline plus on our 3 months old cat, as the instructions stated that it was designed for 2m+ and on our 4y old cat. The 4y old was fine, the kitty became letargic and non-responsive. After the first hour, it stoped moving at all. I searched the internet and found this page with all the symptoms and Mel´s advise to wash the cat several times. My wife washed the cat with soap (Dove), dishwashing liquid and pet´s shampoo. After 1 hour, it opened it´s eyes and we washed again. After a couple hours, it was just a bit letargic and in the next day the kitty was fine.
I belive this product is not safe for younger or older animals, despite what it says in the box/instructions. And I repeat what Mel have said in her post: "as soon as you see symptoms wash your pet". It helps.
Lori - Comment
Lori11 Jul 2018Reply
I put frontline on my 11 year old cat and couldn't find her for two days. I thought she got outside or something I looked everywhere. She finally came out from where ever she was hiding. She had messed all over herself and could barely walk. She walked in circles. I bathed her because she was so stinky and messed up. I think I will wash her again tomorrow agter reading these posts????She makes it! I have been feeding her with a serynge.
Marcos - Comment
Marcos07 Aug 2018Reply
Usei no meu gato de 3 anos e reparei perda de pelo na parte superior do corpo e no pescoço e vermelhidão...estou me preocupando
Isso é normal ?
Beverly Manging - Comment
Beverly Manging20 Aug 2018Reply
I used Frontline on my 11 1/2 month cat 5 days ago hes not stopped scratching bless his heart. Never using this stuff again. Got vets appt on Tuesday evening for injection to help relieve the reaction. Rest of pack in the bin Never using this stuff again !!!!
Karen  - Comment
Karen 08 Sep 2018Reply
I used Frontline on my 11 year old cat. He started being very lethargic, vomiting and not moving. Has not eaten anything for almost two days. Wouldn't walk upstairs. Help what should I do?
Diane - Comment
Diane10 Sep 2018Reply
I've used frontline spot on on both of my Newfoundland dogs and within 12 hours they both developed foul smelling urin and incontinence. I've researched a lot over the day and no one mentions this problem. Can any one help please
Mel - Comment
Mel30 Sep 2018Reply
Please anyone who’s pet is showing any symptoms wash them immediately in fairy dishwashing liquid or dawn dishwashing liquid to remove the toxins from their oil glands
Ariel - Comment
Ariel30 Sep 2018Reply
I use nexguard for my dog works great on my dog and frontline gold on my cats .They seemed to have licked a lot of it off eachother .Will they be okat, I am wondering now and what will happen if my dog snuggles my cats and licks some of the frontline then what will happen ... ????? Will my cats and dog get sick from licking some of the Frontline Gold off eachother?
Joan - Comment
Joan12 Oct 2018Reply
I applied frontline on 4 cats. Their fur is balding at application sight and they are vomiting. I thought this product was better. I had no problems with hartz. Wish I never switched.
Nikki - Comment
Nikki04 Nov 2018Reply
Hi, the vet appled Frontline Spot On (I think it was) to my 4 mth old kitten yesterday afternoon and she's now not herself at all, off food & just lying down looking miserable. I've washed between her shoulder blades where vet applied it. When you say wash the cat, is this sufficient or should I be washing more of her than just the area where it was put on?

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