Although Thujone is the active ingredient in Absinthe people think the magic ingredient is wormwood. Yuck.
"Thujone (C10H16O) is the chemical compound notable for its presence in the alcoholic beverage absinthe. It is a colourless liquid with a distinctive menthol odour. It is a ketone and a monoterpene, and is found in two stereoisomeric forms: (+)-3-thujone or ?-thujone and (-)-3-thujone or ?-thujone. Its formal name is sometimes given as bicyclo(3.1.0)hexan-3-one, 4-methyl-1-(1-methylethyl)-,(1S-(1-, 4-, 5-?))-(9CI); other names include isothujone and thujanone. It is used as a flavouring agent in certain foods and is a compound in a number of other food additives. It boils at 201Â°C and is insoluble in water although it is readily soluble in ethanol or diethyl ether." -Wiki
"A star called Wormwood falls onto the Earth poisoning the freshwater sources such as streams and rivers (This is believed to be a comet that falls but disintegrates before striking; the remains of which fall on the rivers and lakes, thus poisoning the waters. Thousands will die from drinking it. It is believed and accepted by some that believers will be spared this judgment.)" - Wiki