Thujone is a ketone and monoterpene and acts as a neurotoxin in mammals. It occurs naturally in four forms, (−)-α-thujone and (+)-β-thujone as well as (+)-α-thujone and (−)-β-thujone. It has a bitter taste and smells like menthol, which is contained in mint. Thujone acts as a competitive GABA receptor antagonist (it inhibits the inhibitor by blocking its receptor). By inhibiting GABA receptor activation, neurons may fire more easily, which can cause muscle spasms and convulsions. Thujone effects on the central nervous system are documented as side effects from the essential oil of thujone containing plants, which include anxiety, sleeplessness, and convulsions.
Thujone was thought to be responsible for the poisonous effects of the spirit absinthe, for which it was banned. However, recent research has shown that the actual amount in pre-ban (1895–1910) bottles of absinthe was much lower than originally proposed. Today only minute levels of thujone are found in commercially available absinthe. Besides, it has been proposed Thujone would act similar to THC and was considered as a cannabinoid due to a study from the 70ies. However, this has since been proven false.
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