Petco Text Logo
Petco Pet Logo

  • Two Easy Ways to Start Earning Rewards!

My dog is lethargic after Frontline Plus. Is this a medical concern?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed Medium (23 - 60lb) | Female | spayed | 2 years and 5 months old | 50 lbs

My dog is acting very lethargic. The only change in her routine is that I put a dose of Frontline Plus on her back two days ago. Is this cause for concern?

2 Answers

Most Helpful Answer

Image profile

Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on June 2nd, 2017

Lethargy is a very general sign of illness in dogs, and can be caused by systemic illness, infection, inflammation, or injury. Lethargy isn't a side effect of Frontline, so I'm suspecting that it may be to to a medical illness. As long as Scout is eating and drinking normally as well as going to the bathroom normally, I would keep an eye on her for now. Should she still be lethargic in 48 hours, then I would be concerned and take her into the vet for an exam. If she stops eating and drinking, and develops other signs such as vomiting or diarrhea, then I would take her into a vet right away. I hope this helps!

Vote icon

2Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Image profile

    Answered By Jessica Desrosiers

    Veterinary Technician

    Published on

    Lethargy by itself is a very vague sign since it can occur in a number of things. Frontline doesn't tend to cause lethargy, but depending on where you are in the US, things like sudden changes to hot/cold weather may. If there is a reaction to the Frontline, you may see other signs such as redness or irritation at the application site, vomiting, diarrhea, refusal to eat, confusion, etc. If you are seeing other signs of illness, or the lethargy doesn't improve after a day, then seeking vet care is best.

    Vote icon

    1Pet Parents found this answer helpful

See More Answers

Related Questions

Petco Pet Education Center
Health & Wellbeing
What fish dog food helps dry skin if my dog eats Science Diet?
Is your dog's dry skin a concern? A certified vet offers expert advice on finding the best fish-based dog food alternatives to Science Diet for essential oils.
Updated on February 04, 2026
Petco Pet Education Center
Health & Wellbeing
My pet is breathing hard, not eating, and lethargic. What's wrong?
Is your rat breathing heavily, won't eat, and has no energy? A Licensed Vet Tech explains potential causes like infection and age, urging a vet visit for diagnosis.
Updated on December 04, 2025
Petco Pet Education Center
Health & Wellbeing
My dwarf hamster has a shut eye and is limping. What should I do?
Is your dwarf hamster struggling with eye issues or limping? A trusted vet offers expert guidance on symptoms and crucial next steps for comfort and care.
Updated on December 04, 2025
Petco Pet Education Center
Health & Wellbeing
My pet has worsening sores and scratches. Could it be an infection?
Nike's worsening sores and constant scratching worry his owner. A certified Petco veterinarian offers expert guidance on potential causes like bacterial infections and next steps.
Updated on December 04, 2025
Petco Pet Education Center
Health & Wellbeing
Why is my pet's swollen lump with green patches not getting better?
Is your pet's swollen, green-patched infection still bothering them after treatment? A certified veterinarian discusses proper diagnosis methods like biopsy and FNA.
Updated on December 04, 2025
Petco Pet Education Center
Health & Wellbeing
My 4-week-old chick is sick and sleeps standing. What should I do?
Is your 4-week-old chick ill, sleeping standing? A Licensed Vet Tech offers expert advice on immediate care, feeding, and why a vet visit is crucial for diagnosis.
Updated on December 04, 2025
image
Have A Vet Question?

Book an appointment with the pros – our expert vets are here to help.

Book Now

Sponsored