Ingredient of absinthe. Presence in food and beverages regulated by legislation Thujone is a ketone and a monoterpene that occurs naturally in two diastereomeric forms: (-)-alpha-thujone and (+)-beta-thujone. It has a menthol odor. In addition to (-)-alpha-thujone and (+)-beta-thujone, there are their enantiomeric forms, (+)-alpha-thujone and (-)-beta-thujone. (Wikipedia)