The scientific case

~ thujone, fenchone, pinocamphone ~

The distinctive herb in absinthe is grand wormwood (Artemesia absinthium), and the chemical name for the principle active ingredient in wormwood is thujone. Thujone is a terpene and is related to menthol, which is known for its healing and restorative qualities. In its chemically pure form, it is a colourless liquid with a menthol-like aroma. Oil of Artemesia absinthium (or wormwood oil as it’s usually called) is approximately 40-60% thujone. Thujone is a naturally occurring substance, also found in the bark of the thuja, or white cedar, tree, and in other herbs besides wormwood – including tansy and the common sage used in cooking. Aside from absinthe, other popular liquors, including vermouth, Chartreuse, and Benedictine, also contain small amounts of thujone. In fact, vermouth, which was originally made using the flower heads from the wormwood plant, takes its name from the German “wermut” (“wormwood”).

Extremely high doses of thujone are dangerous, and have been shown to cause convulsions in laboratory animals, but the concentration of thujone actually found in absinthe is many thousands of times lower than this.Thujone’s mechanism of action on the brain is not fully understood although certain structural similarities between thujone and tetrahydrocannabinol (the active component in marijuana) led to some speculation in the 1970’s that both substances have the same site of action in the brain. Doubt was cast on this hypothesis almost immediately, and more recent scientific research has completely discredited this idea.

Some researchers have now hypothesised that the reputed “secondary effects” of absinthe have nothing directly to do with thujone at all – if they in fact exist at all, they may be caused by the interaction of some of the other constituent herbs ( fenchone in fennel, pinocamphone in hyssop, and the anethole in anise, have all been shown to cause epileptiform convulsions in laboratory animals when administered in very large doses).

Most modern “legal” absinthes, in keeping with EU regulations, contain less than 10mg of thujone per litre, and recent research has shown that pre-ban Pernod Fils, contrary to ill-informed speculation by several authors, including Strang and Arnold in a widely quoted 1999 British Medical Journal article, also had relatively low thujone levels.
Increasingly it seems clear in fact, that well-made absinthes following authentic traditional recipes seldom have thujone levels much in excess of 35mg/l, the EU standard for thujone in bitters (a category that can, in practice, include absinthe), and many quite naturally fall under the 10mg/l level. It seems that irrespective of the quantity of wormwood used, relatively little thujone makes it through the distilling process into the final distillate. So the entire historical demonization of absinthe based on its allegedly high thujone content now appears to have been based on a wholly false premise.

The high thujone levels claimed by many Czech and German made “absinths” are invariably false (in fact, some of these products, when analysed by gas chromatograph and mass spectrometer, show no detectable thujone at all). More broadly, independent data on the actual thujone level of many contemporary absinthes is often strikingly at variance with the levels claimed by the manufacturers. It’s worth bearing in mind that thujone testing is a complex process, requiring sophisticated equipment and considerably technical experience on the part of the operator. False or anomalous results are not unusual even from laboratories with a reputation for competence, and so all results should be treated with caution, at least until verified by multiple independent testing.

Magnan and other late 19th century French researchers placed guinea pigs in tightly sealed glass jars with saucers of pure wormwood essence, so that they would inhale the fumes. Unsurprisingly the guinea pigs suffered epileptic convulsions and died. These experiments were often used by the temperance movement as proof of absinthe’s toxicity, even though the actual percentage of pure wormwood essence in absinthe is tiny.

Permitted maximum thujone levels in foodstuffs and liquor are:

European Community

(and many other countries, which have adopted the same de facto standards):
– 0.5 mg/kg in food not prepared with sage and non alcoholic beverages.
– 5 mg/kg in alcoholic beverages with 25% or less ABV.
– 10 mg/kg in alcoholic beverages with more than 25% ABV. (Most absinthe falls into this category).
– 25 mg/kg in food prepared with sage.
– 35 mg/kg in alcohol labelled as bitters. (Some absinthe is sold labelled as bitters to allow a higher thujone level).

United States:

Foods or beverages that contain any Artemisia species, white cedar, oak moss, tansy or yarrow must be completely thujone free.
Until recently there was no permitted legal level, however a change in the administrative regulations effective from 2007 defines “thujone free” as less than 10ppm – a similar (but not identical) level to the EU 10mg/l standard. Effectively this opens the door for the first time to the legal sale of at least some absinthes in the USA.
Paradoxically, other herbs that contain thujone have no restrictions at all – for example, sage and sage oil (which can be more than 50% thujone) are on the Food and Drug Administration’s ‘List of Substances Generally Recognized as Safe’.
As a rule of thumb, any absinthe claiming exceptionally high thujone levels should be avoided, as it’s almost certainly a poor quality oil-mix, supported by bogus marketing hype.