Wormwood is Artemisia absinthium, and it is the source of one of the more persistent pieces of misinformation in popular herbalism.
The plant is intensely bitter, the bitterness coming chiefly from absinthin. It flavours vermouth, the word is a French borrowing of German Wermut, wormwood, and it is the defining botanical of absinthe, alongside anise and fennel. Absinthe was banned across much of Europe and in the United States in the years around 1910, after a campaign attributing insanity, convulsions and violence to a supposed poison in the drink.
That poison was identified as thujone, and the identification has not held up. Thujone is genuinely a neurotoxin at high dose, and it is genuinely present in wormwood. But chemical analysis of sealed pre-ban bottles, carried out from the 1990s onward, found thujone concentrations far below what the campaign assumed and generally within the limits now permitted in the European Union. The most economical explanation of absinthe's effects is that it was an extremely strong spirit, frequently around 70 percent alcohol, drunk heavily, and in the cheaper grades adulterated with substances including copper salts and antimony. The ban rested on bad chemistry and on a temperance politics looking for a target.
The plant is bitter enough to be self-limiting in most preparations, and it is a traditional anthelmintic, the English name records the use against intestinal worms, and this is one of the cases where the folk name and the folk use agree.