There is a rare type of poisoning caused by consumption of honey produced from the nectar of rhododendrons, which contain grayanotoxin.
Also called rhododendron poisoning and mad honey intoxication. It lasts for no more than 24 hours, and symptoms are dizziness, weakness, excessive perspiration, low blood pressure, nausea and vomiting shortly after the toxic honey is ingested. The symptoms can occur within a few minutes to several hours after eating the honey.
This is not a problem with commercially produced honey as the pooling of massive quantities of honey during commercial processing generally dilutes any toxic substance.