Wormwood

Artemisia absinthium
For centuries - millenia, really - this herb has been used as a tonic for everything from parasites to pain to liver complaints to baldness. There is a volatile oil in the plant, a narcotic-analgesic related to codeine, that depresses the central medullary part of the brain, dulling anxiety and pain and bringing on a comfortably dreamy state of mind. A chemical found in wormwood called thujone is a powerful nerve and brain stimulator that can trigger libido, but in large amounts may be fatal.
While the name may appear to an English speaker to come from the herb's ability to purge a body of intestinal worms, it is in fact from the German "Wermut", meaning "man courage." Remember that courage as a concept often included sexual valor as well in earlier times. Hippocrates, Pliny, and others recommended its use for aphrodisia.
A drink made from wormwood, absinthe, was very popular during the 19th century, especially amongst European artists. Dr. Pierre Ordinaire created it in 1790 from wormwood, anise, mint, fennel, hyssop, nutmeg, coriander and probably other herbs and spices by steeping them in 136 proof alcohol. Oddly enough, it's sometimes referred to as a fortified wine, but I'm not sure why.
The hazy mindframe caused by continual indulgence in absinthe may in fact be the cause of the Impressionist movement. However, the nervous system can't handle the effects of absinthe overindulgence. Insanity, convulsions, blindness and paralysis are among the most serious side effects, and the French government outlawed the drink in 1915. It is now illegal worldwide, though wormwood itself is not and is still used medicinally by herbalists. Absinthe is still made by some French villages, though secretly, and its mystique has grown enough that there is a market for it.
Reliable recipes for absinthe are rather difficult to come by.
Several drinks used to include wormwood but now legally cannot. Other ingredients provide the bitter flavor now. Most notable in the list are Pernod, Vermouth (which derives from Wermut and wormwood) and Chartreuse (which has the same color as absinthe and gave its name to that color).