Thujone, generally used as a benchmark to measure wormwood content in absinthes.
Thujone is a widely occurring natural product found in the essential oils of two Artemisia species, Artemisia absinthium, and Artemisia pontica. The French liquor absinthe was once prepared from wormwood leaves as well as several other herbs.
Thujone is a monoterpene, or a class of natural products containing ten carbons, found in many different plants and flowers. Monoterpenes are derived from the coupling of two isoprenoid units, which are made from isopentyl pyrophosphate, a precursor in the biosynthesis of cholesterol. These compounds are usually fragrance oils or low melting solids and are used commercially as aroma or flavoring agents. Thujone is structurally related to menthol, which is an old natural remedy for various ailments.
On thujone limits in the UK and EU
While absinthe importation and sales are legal in the UK, as it was never made illegal, they do regulate the amount of thujone (wormwood) allowed. The limit in the UK is 35mg, therefore all absinthes being sold there must comply with this limit.