The Use of St. John's Wort in Dogs & Cats
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Illustration of St. Johns Wort plantThe scientific name for St. John's Wort is Hypericum perforatum. It has been used in dogs to treat obsessive-compulsive behaviors, acral lick dermatitis (lick granulomas), aggression, and separation anxiety.

In humans, it has been used as a sedative, anti-inflammatory, topical analgesic, and antiseptic. It also is used to treat anxiety and to improve the feeling of well-being. Human clinical trials have reported improved sleep quality, an increase in the deep sleep phases, improved cognitive functions, improved mood, and increased level of interest and activity with the use of St. John's Wort.

Do not use St. John's Wort with other antidepressant drugs. Do not discontinue current medications to start St. John's Wort without discussing it with your veterinarian. In people, it takes 2-4 weeks to see an improvement after starting therapy with St. John's Wort.

Large quantities of St. John's Wort consumed by livestock cause photosensitivity. There are reports that St. John's Wort may trigger cataract formation in people who expose themselves to bright light. Hepericin (the active ingredient in St. John's Wort) reacts with visible and ultraviolet light to produce free radicals. This reaction can damage proteins in the eye that give the lens its transparency. The proteins could precipitate and make the lens cloudy, decreasing vision.

The name 'Hypericum' was given by the Greeks to a plant which was placed above religious figures with the purpose of warding off evil spirits. Its common name, St. John's Wort, comes from the fact that its yellow petals 'bleed' when crushed and that it flowers around the 24th of June, the date St. John the Baptist was beheaded. An alternative explanation for the name is that the Knights of St. John of Jerusalem used it to treat wounds during the Crusades. In the Middle Ages, St. John's Wort was commonly used to treat deep sword cuts. Being yellow, the herb was used in the past, according to the Doctrine of Signatures, to treat jaundice and 'choleric humours.'

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