Cats & Dogs
Potentially toxicConsulted references classify the plant as toxic or irritating for that pet type.
Verified against ASPCA/provenance audit 2026-05-06 on May 6, 2026.
Sources
Pet safety reference
St. John's Wort
Hypericum perforatum
Klamath Weed is a perennial flowering plant known for its bright yellow blooms and medicinal history, but it contains compounds that can cause significant health issues if ingested by pets. It is widely recognized as a toxic plant that requires careful management in households with animals.
Common Saint John's WortGoatweedHypericum perforatumSt. John's Wort
- Light
- Full sun to partial shade
- Habit
- Upright, spreading perennial
- Care
- Low
Safety status
If a pet has chewed or swallowed plant material and is showing symptoms, contact a veterinarian or poison resource immediately. This product is for structured reference, not diagnosis.
Cats — concern notes
Common signs
Photosensitivity, skin irritation, drooling, vomiting, and potential neurological changes.
Escalation note
Ingestion can lead to severe skin reactions when exposed to sunlight. Please contact your veterinarian immediately if you suspect your cat has consumed any part of this plant.
Dogs — concern notes
Common signs
Photosensitivity, dermatitis, gastrointestinal upset, and lethargy.
Escalation note
The plant contains hypericin, which can cause increased sensitivity to light and skin inflammation. Seek veterinary care promptly if ingestion is observed or suspected.
Safer alternatives
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Source evidence
ASPCA Toxic Plant List
toxicology · 99% reliability
St. John's Wort is listed as toxic to both cats and dogs due to the presence of hypericin.
NC State Extension Plant Toolbox
botanical · 94% reliability
Hypericum perforatum is a perennial herb that is considered toxic to livestock and pets.
Questions about St. John's Wort
Is St. John's Wort toxic to cats?
Yes, St. John's Wort (Hypericum perforatum) is potentially toxic to cats. It contains compounds that can cause photosensitivity, skin irritation, drooling, vomiting, and potential neurological changes if ingested.
What symptoms does St. John's Wort cause in cats?
The most distinctive danger is photosensitization: cats that ingest St. John's Wort and are then exposed to sunlight can develop ulcerative and exudative dermatitis — open, oozing sores especially on the nose, ear margins, and eyelids. Cats with light or thin fur are particularly vulnerable. Other symptoms include drooling and vomiting.
What should I do if my cat ate St. John's Wort?
Contact your veterinarian immediately and call the ASPCA Animal Poison Control Center at (888) 426-4435. Keep your cat indoors and out of sunlight to reduce the risk of photosensitization reactions while you seek guidance, since sun exposure after ingestion can trigger severe skin lesions.
When do St. John's Wort skin lesions in cats require emergency vet care?
Call your vet any time you see ulceration, weeping skin lesions, or rapidly worsening irritation following suspected exposure. Open, oozing sores — especially around the nose, ear margins, or eyelids — require prompt veterinary attention to prevent secondary infection.
Is St. John's Wort toxic to dogs?
Yes, St. John's Wort (Hypericum perforatum) is toxic to dogs. It contains hypericin, a compound that can cause photosensitivity, dermatitis, gastrointestinal upset, and lethargy if ingested.
What are the symptoms of St. John's Wort poisoning in dogs?
The most distinctive symptom is photosensitization — hypericin makes dogs abnormally sensitive to sunlight, which can cause ulcerative and exudative dermatitis (open, oozing sores) on the nose, ear edges, and areas with thin fur. Dogs may also show gastrointestinal upset and lethargy.
What should I do if my dog ate St. John's Wort?
Contact your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435 immediately. Keep your dog out of sunlight, as hypericin increases light sensitivity and sun exposure can worsen skin damage. Seek veterinary care promptly if ingestion is observed or suspected.
What part of St. John's Wort is dangerous to dogs, and why?
The entire plant contains hypericin, a photosensitizing compound that causes increased sensitivity to light and skin inflammation. This mechanism is what distinguishes St. John's Wort toxicity — the harm can be compounded by sunlight exposure after ingestion, triggering weeping skin lesions especially on lightly furred or unpigmented areas.
Same safety verdict
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