Most herbs that are commonly used in pet healing are very safe and forgiving. In most cases where your pet is sensitive to an herb or has received too much, he will vomit, he may be itchy, or have diarrhea. 

When using herbs, start with a small dose, and watch your pet for any reactions. 

Oxalates – present in many plants, such as Sheep Sorrel – avoid using it with pre-existing kidney or urinary tract disease. – large doses can cause skin lesions (photosensitivity), and can thin the blood causing bleeding.

Anthraquinones – these are the active laxative components that are present in aloe (certain preparations), senna. Anthraquinones act as laxatives by stimulating intestinal peristalsis, and may cause cramping and severe diarrhea if misused.

Berberine – found in Oregon Grape and Goldenseal, will cause vomiting, especially if overused. Avoid in pregnancy or lactation.

Salicylates – this is where Aspirin comes from. Herbs such as White Willow, Poplar, and Meadowsweet should be avoided in all cats.

Tannins – found in Juniper, Black Walnut, and Tea. These can cause irritation if used excessively, especially orally. Avoid in pregnant animals and kidney disease.

Sterols – Licorice is high in these. They can cause high blood pressure and water retention. Avoid this problem by not using it over an extended period of time, and with breaks in therapy.

Essential Oils – There are hundreds of volatile oil compounds that make up the pleasing smell of many plants. Problems occur when the oil is concentrated, then ingested. Pennyroyal, parsley seed, and nutmeg seed are potentially toxic to the liver and kidney if used in overabundance – never use in pregnancy.

The most common toxic herbal reaction that I see is with Tea Tree Oil being used topically with cats and small dogs – they ingest it and become ill. Avoid Tea Tree Oil use with cats and if your dog can lick the area. The compound is hard on the liver and kidneys, and extended use of anthraquinone-bearing herbs may lead to dependency.

Pyrrolizidine (PAs) – This is the toxic part in comfrey – although the risk is slight. There have been only two documented cases of liver damage from Comfrey, while anti-inflammatories such as Rimadyl have caused thousands of cases of liver disease.

Saponins – these are the ‘soap like’ constituents, found in Valerian, Licorice, Yucca. Extended use can produce vomiting/diarrhea. This typically happens in high doses over extended periods of time.