Rhododendron honey (mad honey)

Mad honey from Rhododendron ponticum nectar is produced in large quantity in the western Black Sea region of Turkey.

Many Ericaceae, including Rhododendron, contain diterpene grayanotoxins; honey contamination occurs mainly in the eastern Black Sea region of Turkey, from R. ponticum and R. luteum nectar.

A different, very light rhododendron honey comes from Rhododendron ferrugineum, R. hirsutum and their hybrids in the Alps and Pyrenees, with a colour of 12.4 ± 4.0 mm Pfund and under-represented pollen.

Harmonised melissopalynology gives a relative frequency of 15 to 77 percent for Rhododendron pollen in unifloral rhododendron honeys, a type that can be under-represented in some cases.

Grayanotoxins are diterpenes, polyhydroxylated cyclic hydrocarbons, and more than 25 isoforms have been isolated from Rhododendron.

Grayanotoxin 1 and 3 are currently thought to be the principal toxic isomers, and grayanotoxin 1 and 2 have been found in the honey, leaves and flowers of Rhododendron ponticum.

The toxicity of grayanotoxin is attributed to its ability to bind to the group II receptor site in voltage-gated sodium channels.

In Turkish mad honey from three consecutive years, mean grayanotoxin I and III contents were 20.4 ± 1.69 and 8.20 ± 1.93 mg/kg, unchanged after six months of storage.

A systematic review of 1199 cases reported between 1981 and 2014 found that the most common complaints were dizziness, nausea and presyncope, and that no deaths were reported.

The review attributes the poisonings to honey made from the nectar of Rhododendron ponticum and Rhododendron luteum flowers.

Symptoms of grayanotoxin poisoning most often occur within 20 minutes to 3 hours after ingestion and remain for 1 to 2 days; in humans the intoxication is rarely lethal.

Grayanotoxin-containing honey, called mad honey, was already recorded by Xenophon in 401 BC in his Anabasis; old and recent cases of wild honey poisoning are also reported from Nepal.