My dog ate antihistamines – what should I do?

Updated 2026-09-30 · 1 sources

Based on: Pet Poison Helpline

Call a vet today

Call your vet today for advice – don't wait until signs appear. An antihistamine overdose can affect the nervous system and heart, causing depression, over-stimulation or gastrointestinal distress.

What to do now

What to do right now

Call your vet or the nearest emergency vet.
Note what was eaten, how much and when.
Bring the packaging.
Keep your dog calm.
Remove what is left.

Don't

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

Why it can be dangerous

Antihistamines are used in human and veterinary medicine for upper respiratory and dermal allergies.^[1] An accidental antihistamine overdose can result in neurological or cardiovascular depression or hyperstimulation and gastrointestinal distress.^[1]

Signs to watch for

Depression

Where it is found

Human medicine
Veterinary medicine

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.

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

Common questions

How much antihistamine is dangerous?

Call your vet for advice about how much your dog ate.

Which signs should I watch for?

Depression can occur after an accidental antihistamine overdose.^[1]

How soon should I act, and what should I do?

Call your vet today for advice – don't wait until signs appear.

Sources

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 cats →