“WHAT INGREDIENT(S) IN ABSINTHE ARE PSYCHOACTIVE?
ETHANOL

Ethanol (normal drinking alcohol) is definitely one main active component. Undiluted absinthe was anywhere from 60% to 85% ethanol. Although some, such as Alfred Jarry, were known to have drunk it straight, it was usually substantially diluted. Still, dilution could not change the fact that absinthe contained a lot of ethanol in comparison to its other ingredients.
THUJONE

Another candidate is the monoterpene, thujone, which is considered a psychoactive convulsant. The sources of thujone in absinthe are the herbs wormwood (Artemisia absinthium) and Roman wormwood (Artemisia pontica). There is good evidence that both thujone and wormwood have psychoactive properties. Some have suggested that this effect is due to thujone binding at the cannabinoid receptor, at which the active components in marijuana act (delCastillo et al 1974). This seems unlikely. Furthermore, it is not even clear that thujone is present in sufficient quantities to play a role in absinthe intoxication. However, it is possible that thujone accumulates in the body and plays a role in the psychoactivity and toxicity of chronic absinthe use. ”