My cat ate fluorouracil—what should I do?

Updated 2026-09-30 · 2 sources

Based on: US FDA – Center for Veterinary Medicine, Pet Poison Helpline

Call a vet now

Call your vet or the nearest emergency vet right now. Signs of fluorouracil poisoning can start within 30 minutes after ingestion.

What to do now

What to do right now

  1. Call your vet or the nearest emergency vet.
  2. Note what, how much and when.
  3. Bring the packaging.
  4. Keep your cat calm.
  5. Remove what is left.

Don't

  • Do not make your cat vomit unless a vet tells you to.
  • Do not give any human medicine.

Why it can be dangerous

Topical fluorouracil (5-FU) is one of the most dangerous pet toxins.[2] Signs of fluorouracil poisoning can start within 30 minutes after a pet ingests the medicine.[1] The prognosis for cats that ingest the medicine is grave.[1]

Signs to watch for

  • vomiting
  • diarrhea
  • tremors
  • seizures
  • death

Clinical signs can occur within 30 minutes to 6 hours.

Where it is found

  • topical treatments for human skin cancers
  • actinic keratosis

What the experts say

“However, the Pet Poison Helpline states that the prognosis for cats that ingest the medicine is grave.”

— US FDA – Center for Veterinary Medicine [1]
If your pet is struggling to breathe, has collapsed, is having a seizure or can't stand up: go to the nearest vet now.

Not sure how serious it is?

OkPaw asks a few quick questions about your pet and tells you in 30 seconds whether it can wait. Free on Google Play for Android.

Get it on Google Play

OkPaw is on Android now – an iPhone version is on its way.

Common questions

How soon could signs start?

Signs of fluorouracil poisoning can start within 30 minutes after a pet ingests the medicine.[1]

What should I do now?

Call your vet or the nearest emergency vet right now.

Sources

  1. US FDA – Center for Veterinary Medicine
  2. Pet Poison Helpline

How this page was made: written with the help of AI from the sources below, then checked claim by claim against those sources. Urgency levels follow OkPaw’s fixed safety rules. It is guidance, not a diagnosis. How we write our pages

The same page for dogs →

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