Henbane (Hyoscyamus niger, also black henbane and stinking nightshade) is a poisonous plant belonging to tribe Hyoscyameae of the nightshade family Solanaceae. Henbane is native to temperate Europe and Siberia, and naturalised in Great Britain and Ireland.

The name henbane dates from AD 1265; "bane" meant 'thing that causes death'. Other etymologies of henbane derive from the Indo-European stem bhelena meaning "crazy plant" and with the Proto-Germanic element bil meaning "vision", "hallucination", "magical power", and "miraculous ability".

Historically, henbane was used in combination with other plants, such as the mandrake, the deadly nightshade, and datura, as an anaesthetic potion, and for its psychoactive properties in "magic brews". These psychoactive properties include visual hallucinations and a sensation of flight. It was originally used in continental Europe, Asia, and the Arab world, though it did spread to England in the Middle Ages. The use of henbane by the ancient Romans was documented by Pliny, who said it was "of the nature of wine and therefore offensive to the understanding", and by Dioscorides, who recommended it as a sedative and analgesic.

The plant, recorded as Herba Apollinaris, was used to yield oracles by the priestesses of Apollo. Recently evidence for its use in the earlier British Neolithic has been debated. John Gerard's Herball states: "The leaves, the seeds and the juice, when taken internally cause an unquiet sleep, like unto the sleep of drunkenness, which continueth long and is deadly to the patient. To wash the feet in a decoction of Henbane, as also the often smelling of the flowers causeth sleep."

The plant was also purportedly used as a fumigant for magical purposes. Albertus Magnus, in his work De Vegetalibus (1250), reported that necromancers used henbane to invoke the souls of the dead as well as demons. Henbane was already being demonized as early as the Late Middle Ages when it became inseparably associated with witchcraft and malefic practices. "The witches drank the decoction of henbane and had those dreams for which they were tortured and executed. It was also used for witches' ointments and was used for making weather and conjuring spirits. If there were a great drought then a stalk of henbane would be dipped into a spring, then the sun-baked sand would be sprinkled with this" (Perger 1864, 181).

Henbane was discovered among an assortment of imported spices during the underwater archaeological excavation of the royal Danish-Norwegian flagship, Gribshunden, which sank in 1495 near Ronneby, Sweden. The purpose of this henbane is not known, but could have been medicinal for soothing toothache, or as an anti-emetic and to prevent motion sickness.

During a Pomeranian witchcraft trial in 1538, a suspected witch "confessed" that she had given a man henbane seeds so that he would run around "crazy" (sexually aroused). In a file from an Inquisition trial, it was noted that "a witch admits" having once strewn henbane seeds between two lovers and uttering the following formula: "Here I sow wild seed, and the devil advised that they would hate and avoid each other until these seeds had been separated" (Marzell 1922, 169).

Henbane was one of the ingredients in gruit, traditionally used in beers as a flavouring. The recipe for henbane beer includes 40 g dried chopped henbane herbage, 5 g bayberry, 23 L water, 1 L brewing malt, 900 g honey, 5 g dried yeast, and brown sugar. Henbane fell out of usage for beer when it was replaced by hops in the 11th to 16th centuries; in Bavaria the Purity Law of 1516 outlawed ingredients other than barley, hops, yeast, and water.