"Mmh, maybe it's that because it does have medical properties, both common and magical.

"For one, the medicinal use of the berries was familiar to all the writers on botany and materia medica of the sixteenth century, though Dodoens in his Herbal wrote: 'They be not meat to be administered but to the young and lusty people of the country which do set more store of their money than their lives.' That might be a magical; de-lusting?"

"Then it has purgative properties: The herb bruised and applied to warts will make them consume and waste away in a short time. Indeed, Buckthorn can still be used as an ointment to treat warts. The bruised herb is applied to warts to consume them AND the leaves bruised and applied to a wound will stop the bleeding."

"The botanical name catharticus gives an indication of its laxative or purging properties. Buckthorn is also known as Hart's-horn or the Purging Buckthorn. The ointment also relieves pruritus."