Henbane has a long documented medical history in exactly the role its chemistry suggests: as a soporific and a pain-deadener, used when there was nothing better, by people who knew it could kill.
Dioscorides describes it in the De Materia Medica in the first century, distinguishing the black, yellow and white forms and warning that the black produces madness and sleep. Arabic and medieval European medicine used it in the soporific sponge, a preparation of henbane, opium and mandrake soaked into a sponge and held to the face of a patient before surgery. That is a genuine and serious pre-modern anaesthetic tradition, and its problem was always the same: the margin between a dose that dulls and a dose that kills is narrow, and neither the concentration in the plant nor the dose delivered could be controlled.
Henbane also has a documented use in brewing. Before hops became standard, gruit ales in parts of northern Europe were bittered with mixtures of herbs, and henbane is named among them. The German Bilsenkraut is preserved in the place name Pilsen in one popular etymology, which is disputed and should not be relied on.
The English name is straightforward and grim: bane of hens, from the plant's reputation for killing poultry. Old English forms are attested from well before the Norman conquest, and henbane is among the plants named in Anglo-Saxon medical writing.
Henbane has a documented criminal history to match. Hawley Harvey Crippen was convicted in 1910 of poisoning his wife with hyoscine, in a case that turned on some of the earliest forensic toxicology admitted in an English court, and that was the first murder investigation in which a suspect was apprehended by wireless telegraph. Shakespeare's hebona or hebenon, poured in the ear of Hamlet's father, is often identified with henbane, though the identification is disputed and yew and ebony have also been proposed.