I photographed this tansy in the Swamp this morning; it contain a volatile oil which can cause contact dermatitis in sensitive individuals. If taken internally, toxic metabolites are produced as the oil is broken down in the liver and digestive tract. It is highly toxic to internal parasites, and for centuries tansy tea has been prescribed by herbalists to expel worms. Tansy is an effective insecticide and is highly toxic to arthropods. Tanacetum annuum is often confused with common tansy (Tanacetum vulgare) but the former produces an essential oil that is completely different chemically as it contains no thujone and high amounts of chamazulene making the oil dark blue in colour, giving rise to it common name of Blue Tansy Oil. Despite claims by some unethical resellers of essential oils who adulterate the very expensive Blue Tansy (Tanacetum annuum) oil with the much cheaper oil from Tanacetum vulgare, it should be noted that the oil from Tanacetum vulgare is never blue in colour as it contains no chamazulene. For this reason a high thujone oil from Tanacetum vulgare should never be referred to as “Blue Tansy” oil and any such blue oil containing significant thujone is an adulterated product.
The active components of the volatile oil include 1,8-cineole, trans-thujone, camphor and myrtenol, with the quantities and proportions of each varying seasonally and from plant to plant.
1,8-Cineole is a toxin believed to defend the plant leaves against attacks by herbivores.