Poison takes a leading role in Hamlet, as sibling rivalry leads to regicide and throws the Danish royal castle at Elsinore into a state of jealously and mistrust.
King Hamlet, father to Prince Hamlet and brother to Claudius dies seemingly in his sleep, but the young prince soon discovers that poison in the ear was in fact the cause.
Scientists and scholars have wondered what Shakespeare meant by "cursed hebenon". There may be a few possibilities including hemlock, nightshade, yew, ebony and henbane.
Indeed henbane looks the closest in spelling, and the active ingredient in henbane is hyoscyamine which if concentrated to a high degree could be lethal to humans. Perhaps this is what Shakespeare is referring?