Absinthe

This potent, anise flavoured spirit is not really a true liqueur. It was, for years, banned in most countries because of the toxic quality of one of its essential ingredients: wormwood, considered to have hallucinogenic properties. Today, while it is commercially available in many parts of the world, it is difficult to find “true” absinthe.

From Wikipedia:
Absinthe... is an anise-flavoured spirit derived from botanicals, including the flowers and leaves of Artemisia absinthium ("grand wormwood"), together with green anise, sweet fennel, and other medicinal and culinary herbs.

Absinthe traditionally has a natural green colour, but may also be colourless. It is commonly referred to in historical literature as "la fée verte" (the green fairy). It is sometimes mistakenly referred to as a liqueur, but it is not traditionally bottled with added sugar and is, therefore, classified as a spirit. Absinthe is traditionally bottled at a high level of alcohol by volume, is normally diluted with water before being consumed.

Absinthe originated in the canton of Neuchâtel in Switzerland in the late 18th century. It rose to great popularity as an alcoholic drink in late 19th- and early 20th-century France, particularly among Parisian artists and writers.

Absinthe has often been portrayed as a dangerously addictive psychoactive drug and hallucinogen. The chemical compound thujone, which is present in the spirit in trace amounts, was blamed for its alleged harmful effects. By 1915, absinthe had been banned in the United States and in much of Europe, including France, the Netherlands, Belgium, Switzerland, and Austria–Hungary, yet it has not been demonstrated to be any more dangerous than ordinary spirits. Recent studies have shown that absinthe's psychoactive properties have been exaggerated, apart from that of the alcohol.

The classic way to serve absinthe, drizzled over a cube of sugar.