Why is it dangerous to pets?
Levothyroxine is a thyroid hormone. A pet that swallows several tablets becomes acutely hyperthyroid: heart rate and body temperature climb, and the pet becomes agitated and trembles.
Because many pets take this drug daily, the bottle is often within reach — and a chewed bottle can mean dozens of tablets at once.
Why speed matters
Delaying care significantly worsens outcomes. Some signs appear hours or days later, so "looks fine right now" is not a reason to wait.
Symptoms of thyroid-meds poisoning
- Restlessness, agitation, pacing
- Fast heart rate, panting, high body temperature
- Vomiting, diarrhoea
- Tremors, muscle twitching
- Irregular heartbeat, seizures (severe overdose)
What to do right now
- Call your vet or a poison line and count how many tablets are missing.
- Bring the bottle — strength varies from 25 µg to 200 µg per tablet.
- Do not give the next scheduled dose until the vet says so.
- Keep medication in a closed cabinet, never on a counter or bedside table.
Sources & further reading
- ASPCA Animal Poison Control — pet poison database & dosage references
- Pet Poison Helpline — toxicology triage guidelines
- Merck Veterinary Manual — toxicology monographs
- Vets Now (UK) — emergency toxicosis guidance
Other poisonings with overlapping signs
- 5-HTP & Herbal Supplements — shares signs: tremors, fast heart rate, vomiting
- Antidepressant (SSRI) Poisoning — shares signs: restlessness, vomiting
- Decongestants (Pseudoephedrine, Phenylephrine) — shares signs: restlessness, vomiting
Owners also ask
- Is 5-HTP more dangerous for kittens than adult cats?
- My dog just ate one of my antidepressant pills (SSRI like Prozac) — what do I do?
Frequently asked questions
Is Thyroid Medicines (Levothyroxine) poisonous to a dog or cat?
Levothyroxine is a thyroid hormone. A pet that swallows several tablets becomes acutely hyperthyroid: heart rate and body temperature climb, and the pet becomes agitated and trembles.
What are the symptoms of thyroid-meds poisoning?
Restlessness, agitation, pacing; Fast heart rate, panting, high body temperature; Vomiting, diarrhoea; Tremors, muscle twitching
What should I do if my pet ate Thyroid Medicines (Levothyroxine)?
Call your vet or a poison line and count how many tablets are missing. Bring the bottle — strength varies from 25 µg to 200 µg per tablet. Do not give the next scheduled dose until the vet says so.
Not the substance you were looking for? Every question answered.