Is there any type of honey that is toxic to humans?

Mad honey is different from commercial/marketed honey as it is contaminated with grayanotoxin; ... [which is] extracted by honey bees from the nectar and pollen of the plants of the Rhododendron genus (Ericaceae family), most commonly from R. luteum, R. flavum, R. simsii, and R. ponticum.

...mad honey was used by King Mithradates IV (Northeast Anatolia, Turkey) as a weapon in 67 BC against Pompey the great.