Choker of Venomous Words

Wondrous item, rare (requires attunement by a bard, cleric, or druid)

This choker clasps around your throat with a discreet hinge and then magically slithers as it resizes to fit. The choker has 3 charges and regains all expended charges daily at dawn. While wearing it, you can use a bonus action to expend 1 or more of its charges to cast either healing word (1 charge) or mass healing word (2 charges), using your spellcasting ability modifier.

Whenever you cast healing word or mass healing word while wearing the choker, you can choose to change the nature of the spell for one or more affected targets. When you do, a target affected by the changed spell must make a Constitution saving throw, using your spell save DC. On a failed save, a target takes poison damage equal to the number of hit points the spell would normally restore and is poisoned until the end of your next turn. On a successful save, a target takes half as much damage and isn't poisoned. A creature that can’t be poisoned can still be poisoned in this way unless it has an Intelligence of 3 or lower.

"Even the sweetest words you once revered can turn bitter and poison your soul, if you twist their meaning just a little."