Beware the rhododendron! (That’s the flower seen here.) There’s an interesting case report in the American Journal of Emergency Medicine from Turkey describing a man with NSTEMI (EKG changes and the release of a chemical in the blood indicating heart injury) after eating mad honey, which is apparently honey made from the pollen of some species of flowers, especially the rhododendron. These flowers’ pollen contain grayanotoxin, a class of chemicals that block repolarization of excitable cell membranes (nerve and muscle). Symptoms seem to be pretty cholinergic–diarrhea, nausea, vomiting, sweating–according to this review article in Food and Chemical Toxicology.
Interestingly it appears that mad honey is attributed with destroying more than a few armies in ancient history.