From http://www.thujone.info/thujone-absinthe-3.html
Habitual abuse of the wormwood spirit absinthe was described in the 19th and 20th centuries as a cause for the mental disorder “absinthism” including the symptoms hallucinations, sleeplessness and convulsions. A controversial discussion is going on if thujone, a characteristic component of the essential oil of the wormwood plant Artemisia absinthium L., is responsible for absinthism, or if it was merely caused by chronic alcohol intoxication or by other reasons such as food adulterations.
To ascertain if thujone may have caused absinthism, absinthes were produced according to historic recipes of the 19th century. Commercial wormwood herbs of two different manufacturers, as well as self-cultivated ones, were used in a concentration of 6 kg/100 l spirit. In addition, an authentic vintage Pernod absinthe from Tarragona (1930), and two absinthes from traditional small distilleries of the Swiss Val-de-Travers were evaluated. A GC–MS procedure was applied for the analysis of a- and ß-thujone with cyclodecanone as internal standard. The method was shown to be sensitive with a LOD of 0.08 mg/l. The precision was between 1.6 and 2.3%, linearity was obtained from 0.1 to 40 mg/l (r = 1.000).
After the recent annulment of the absinthe prohibition all analysed products showed a thujone concentration below the maximum limit of 35 mg/l, including the absinthes produced according to historic recipes, which did not contain any detectable or only relatively low concentrations of thujone (mean: 1.3 ± 1.6 mg/l, range: 0–4.3 mg/l). Interestingly, the vintage absinthe also showed a relatively low thujone concentration of 1.8 mg/l. The Val-de-Travers absinthes contained 9.4 and 1.7 mg/l of thujone.
In conclusion, thujone concentrations as high as 260 mg/l, reported in the 19th century, cannot be confirmed by our study. With regard to their thujone concentrations, the hallucinogenic potential of vintage absinthes can be assessed being rather low because the historic products also comply with today's maximum limits derived to exclude such effects. It may be deduced that thujone plays none, or only a minor role in the clinical picture of absinthism.