Is White Snakeroot Toxic to Dogs and Cats? (2026)
Ageratina altissima
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Quick facts
| Toxic to dogs | Yes |
|---|---|
| Toxic to cats | Yes |
| Toxic to horses | Yes |
| Toxic component | Tremetol |
| Onset of symptoms | Develops over days of continued exposure rather than a single bite |
| Indoor / outdoor | outdoor |
If your pet ate this plant
Both lines are staffed 24/7. A consultation fee applies to each. Do not wait for symptoms to appear before calling.
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Symptoms in dogs
- Tremors
- Weakness
- Loss of coordination
Symptoms in cats
- Tremors
- Weakness
Symptoms in horses
- Tremors
- Weakness
- Can be fatal with sustained grazing
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What to do
Contact a vet for any suspected exposure. This is the same tremetol-containing plant responsible for historical "milk sickness" outbreaks, including the illness that killed Abraham Lincoln's mother.
Toxic component and mechanism
The toxic component in White Snakeroot is tremetol.
What makes this plant different
White Snakeroot gained historical notoriety as the plant responsible for 'milk sickness,' the illness that reportedly killed Abraham Lincoln's mother, Nancy Hanks Lincoln — the toxin passes through a grazing cow's milk to anyone who drinks it, a genuinely unusual secondary-exposure risk.
Plant identification
- Scientific name
- Ageratina altissima
- Family
- Asteraceae
- Also known as
- White Snakeroot, Richweed, White sanicle
- Typically found
- outdoor
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Last verified: July 2, 2026 · Cross-referenced with ASPCA Animal Poison Control