If you read into any of the literature you will find strong warnings about this everywhere. This plant is extremely poisonous. They were aware of its dangerous properties in period, and such it was given names such as devils berries, devils herb, divale, and naughty man's cherries.
It was widely dispersed across central and southern Europe, growing a few feet high. The dark green leaves grow 3-10 inches long and have a bitter taste.
The entire plant (particularly leaves and roots) contains Atropine, which is a poisonous alkaloid. It's reputed as being the plant that poisoned the troops of Marcus Antonius during the Parthian wars. Its use is also revealed in stories of when Duncan I was King of Scotland, the soldiers of Macbeth poisoned a whole army of invading Danes by a liquor mixed with an infusion of Belladonna supplied to them during a truce, and were murdered in their sleep by the Scots. The plant is also well reputed with witches of the time and was an ingredient in many hallucinogenic concoctions and ointments.
The name Belladonna, which translates as Beautiful Lady in Italian, refers to a bizarre custom in which Italian women would drop the sap of the plant into their eye to dilate the pupils, in order to make them appear more attractive. The reason for doing this is that when we see something we like, our pupils dilate. At a subconscious level we notice when someone else's eyes are dilated and would interpret this as a sign that they are attracted to us. Obviously, this would make them attractive to us.