Thomas Prisinzano, Graduate Student Department of Medicinal Chemistry Medical College of Virginia Campus, Virginia Commonwealth University writes:
Absinthe drinkers were reported to have experienced a double action intoxication . This intoxication combined the separate effects of alcohol and thujone. The alcohol produced a sedative effect in absinthe drinkers while the thujone is reported to have caused hallucinations (both visual and auditory) as well as excitation.The only proven effect of thujone, however, is its toxicity to the brain. The toxicity of thujone in the brain is believed to result from its structural similarity to tetrahydrocannibinol, or THC , the active compound in marijuana.
Cannabis has been used for centuries for medicinal purposes and has great therapeutic potential.
Thujone and THC have similar shapes, and it is believed that they interact with the same biological receptor to produce their similar psychological effects. The similarities between the molecules include gem dimethyl groups and a similar carbon framework. It is also believed that the hydroxyl group of THC and the carbonyl of thujone may interact at the same site. Modeling studies show a good degree of overlap.
For a while it was hypothesized that thujone and tetrahydrocannabinol had the same site of action. This was believed to be true because of the similarities in their structures and effects. But in 1997, it was shown that neither thujone nor wormwood binds to the canabinoid receptor.
http://chemweb.calpoly.edu/chem/bailey/377/PapersSp2000/Ann/absinthe.html