Thujone

Thujone is a ketone and a monoterpene that occurs naturally in two diastereomeric forms: (−)-α-thujone and (+)-β-thujone. It has a menthol odor. Even though it is best known as a chemical compound in the spirit absinthe, recent tests show absinthe contains only small quantities of thujone, and may or may not be responsible for absinthe's reported psychedelic effects. Thujone acts on GABA and 5-HT3 receptors in the brain. In many countries the amount of thujone allowed in food or drink products is regulated.

In addition to (−)-α-thujone and (+)-β-thujone, there are their enantiomeric forms, (+)-α-thujone and (−)-β-thujone:

Pharmacology
Based on studies that looked only at molecular shape, for many years thujone was thought to act similarly to THC on the cannabinoid receptors. Today this is known to be false because studies have shown that thujone does not activate these receptors. Thujone is a GABAA receptor antagonist. By inhibiting GABA receptor activation, neurons may fire more easily which can cause muscle spasms and convulsions. Thujone is also a 5-HT3 antagonist.

A toxicology study in mice of alpha-thujone, the more active of the two isomers, found that the median lethal dose, or LD50, is around 45 mg/kg, with 0% mortality rate at 30 mg/kg and 100% at 60 mg/kg. Mice exposed to the higher dose had convulsions that led to death in 1 minute. From 30 to 45 mg/kg the mice experienced muscle spasms in the legs which progressed to general convulsions until death or recovery. Pretreatment with diazepam, phenobarbital or 1 g/kg of ethanol protected against a lethal 100 mg/kg dose. These findings are in line with other GABA antagonists. The study also found that alpha-thujone was metabolized quickly in the liver.

Researchers at Rutgers University tested attention performance with low and high doses of thujone in alcohol. The researchers administered 0.28 mg/kg in alcohol, 0.028 mg/kg in alcohol and just alcohol to their subjects. The high dose had a short term negative effect on attention performance. The lower dose showed no noticeable effect.

Thujone is reported to be toxic to both brain and liver cells and could cause convulsions if used in too high a dose. Other thujone-containing plants such as the tree Arborvitae (Thuja occidentalis) are used in herbal medicine, mainly for their immune-system stimulating effects. Side-effects from the essential oil of this plant include anxiety and sleeplessness, which confirms the central nervous system effects of thujone.

Thujone in absinthe
Thujone is most famous for being a compound in the spirit absinthe. In the past it was thought that absinthe contained up to 260–350 mg/L thujone, but modern tests have shown this to be far too high. A 2008 study of 13 pre-ban (1895–1910) bottles using gas chromatography-mass spectrometry (GC-MS) found that the bottles had between 0.5 mg/L and 48.3 mg/L and averaged 25.4 mg/L A 2005 study recreated three 1899 high-wormwood recipes and tested with GC-MS, and found that the highest contained 4.3 mg/L thujone. GC-MS testing is important in this capacity, because gas chromatography alone may record an inaccurately high reading of thujone as other compounds may interfere with and add to the apparent measured amount.

Absinthe produced under the modern EU (European Union) limits for thujone content may have a maximum of 10 mg/L if >25% alcohol, and 35 mg/L for "bitters" with less alcohol. Some modern producers list their thujone levels on the bottle, with some producers claiming over 100 mg/L thujone.

History
The compound was discovered after absinthe became popular in the mid-19th century. Dr. Valentin Magnan, who studied alcoholism, tested pure wormwood oil on animals and discovered it caused seizures independent from the effects of alcohol. Based on this, it was assumed that absinthe, which contains a small amount of wormwood oil, was more dangerous than ordinary alcohol. Eventually thujone was isolated as the cause of these reactions. Magnan went on to study 250 abusers of alcohol and noted that those who drank absinthe had seizures and hallucinations. In light of modern evidence, these conclusions are questionable, as they are based on a poor understanding of other compounds and diseases, and clouded by Magnan's belief that alcohol and absinthe were "degenerating" the French race.

After absinthe was banned, research dropped off until the 1970s when the British scientific journal Nature published an article comparing the molecular shape of thujone to tetrahydrocannabinol (THC), the primary psychoactive substance found in cannabis (marijuana), and hypothesized it would act the same way on the brain, sparking the myth that thujone was a cannabinoid.

More recently, following European Council Directive No. 88/388/EEC (1988) allowing certain levels of thujone in foodstuffs in the EU, the studies described above were conducted and found only minute levels of thujone in absinthe.

European Union
Maximum thujone levels in the EU are:
 * 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.
 * 25 mg/kg in food prepared with sage.
 * 35 mg/kg in alcohol labeled as bitters.

United States
Foods or beverages that contain Artemisia species, White Cedar, oak moss, tansy or Yarrow must be thujone-free. Other herbs that contain thujone have no restrictions. For example, sage and sage oil (which can be up to 50% thujone) are on the Food and Drug Administration's list of substances generally recognized as safe. Absinthe offered for sale in the United States must be "thujone-free", which is interpreted as containing less than 10 mg/kg. There are now therefore a number of thujone-containing absinthes that can be legally imported.

Canada
In Canada, liquor laws are the domain of the provincial governments. British Columbia has no limits on thujone content; Alberta, Ontario and Nova Scotia allow 10 mg/kg thujone; Québec allows 15 mg per kg ; Manitoba allows 6–8 mg thujone per litre; and all other provinces do not allow the sale of absinthe containing thujone (although, in Saskatchewan, one can purchase any liquor available in the world upon the purchase of a maximum of one case, usually twelve 750-mL bottles or 9L). The individual liquor boards must approve each product before it may be sold on shelves.