Absinthe thujone is the chemical found in Absinthe’s vital ingredient, the plant called Common Wormwood, or Artemisia Absinthium to give it its botanical name. The substance thujone was partly responsible for Absinthe being banned in the early 1900s in many countries across the world and thujone is still tightly regulated today http://absinthesupreme.com, particularly in the United States (or states united).
Thujone was considered to be much like THC seen in cannabis and Absinthe was speculated to be psychoactive and have psychedelic effects triggering hallucinations and insanity. Absinthe was well-liked by the Bohemian set in Montmartre in Paris and many artists and writers believed that Absinthe, the Green Fairy, gave them inspiration in addition to their genius. Well-known Absinthe drinkers include Oscar Wilde, Ernest Hemingway, Van Gogh, Gauguin, Degas, Baudelaire and Verlaine. Some claim that Van Gogh’s madness was caused by Absinthe and that he cut off his ear under its effect 
. Absinthe was even held accountable for a man murdering his family, although he had taken a number of other strong alcoholic drinks following the Absinthe.
Prohibition campaigners used news of the murder to campaign for the outlawing of Absinthe and blamed France’s growing problems of alcoholism to the emerald liquor.
Is Absinthe Thujone Dangerous?
Today’s research suggests that it was in fact the alcohol (ethanol) content of Absinthe which was dangerous rather than the thujone. Absinthe is two times as strong as spirits like whisky and vodka and can be 75% alcohol. Care should therefore be taken when consuming Absinthe. Thujone is merely present in minute quantities and must therefore cause no major negative effects or health conditions. The EU stipulates that alcoholic beverages with an ABV (alcohol by volume) level over 25% may only consist of a maximum of 10mg/kg of thujone, beverages classed as “bitters” can contain up to 35mg/kg, it’s not totally clear which class Absinthe fits into but most brands of Absinthe have much less than 35mg with many being under 10mg/kg. In the US it is only legal to purchase or sell Absinthes with trace amounts of thujone.
High doses of thujone can be dangerous leading to convulsions but you will have to drink a great deal of Absinthe to consume that volume of thujone and it will be impossible to drink that amount, you’d be comatosed from alcohol until then!
Absinthe Formula
It is known that Henri-Louis Pernod, who owned the very first Absinthe distillery, used the herbs wormwood, aniseed, fennel, lemon balm, hyssop, angelica root, dittany, star anise, nutmeg, juniper and veronica to create his famous Pernod Absinthe. The essential oil from all of these herbs is responsible for La Louche, the clouding which occurs when water is added to Absinthe. These herbs specially the aniseed and anise are responsible for the distinctive aniseed or licorice taste of Absinthe and wormwood is responsible for the bitter flavor. Absinthe is sometimes used as bitters in cocktails.
There are many brands of Absinthe or Absinthe substitutes which were developed in the ban and so contain no Absinthe thujone or wormwood, however, many would state that Absinthe is not Absinthe without Absinthe thujone and the bitter taste of wormwood. If you’d like real Absinthe search for brands that contain wormwood or Absinthe thujone.