Can honey be poisonous? Tutin, grayanotoxins and the law

The short answer

Bees gather from thousands of plants, and a handful of those make compounds that are toxic to people. In almost every case the quantities reaching honey are negligible, blending dilutes them further, and the plants are not important honey sources. Two exceptions are documented well enough to have their own case histories, and one of them has its own law.

Tutin: a toxin that arrives through an insect

1. 1The plantTutu, Coriaria arborea, is a native New Zealand shrub whose sap contains tutin, a neurotoxin.
2. 2The insectThe passion vine hopper, Scolypopa australis — native to Australia and introduced to New Zealand in the 1800s — feeds on tutu sap and excretes the excess as honeydew, carrying tutin with it.
3. 3The beeHoney bees collect that honeydew, and the tutin goes into the honey. Risk is highest for honey harvested between 1 January and 30 June.

Poisonings from tutin honey have occurred in New Zealand sporadically since the late 19th century, and at least twenty people were poisoned in 2008. New Zealand brought in an emergency standard that took effect in January 2009, limiting tutin to 2 mg/kg in extracted honey and 0.1 mg/kg in comb honey. Research then found that honey also carries tutin glycosides — tutin with glucose attached — which the human gut can convert back into tutin, some people very efficiently. Because the true dose could therefore be higher than a tutin measurement shows, the limit was lowered to 0.7 mg/kg for all honey, comb included.

The risk is geographic. The hoppers are found mainly on tutu north of latitude 42° south, and areas further south are not thought to be at risk. The regulator's review named northern Hawke's Bay, the Bay of Plenty and the Coromandel as the highest-risk areas, with poisonings also reported in the Marlborough Sounds and Northland — and estimated that about 72 per cent of New Zealand's honey by volume came from high-risk areas. In laboratory results for the year to June 2014, 3.8 per cent of single honey samples tested exceeded 0.7 mg/kg, which is why honey from those areas and seasons is tested before sale.

Grayanotoxins: mad honey and its alpine relative

Certain rhododendrons carry grayanotoxins in their nectar. Honey from Rhododendron ponticum and R. luteum on the Black Sea coast is the 'mad honey' sold deliberately for its effect, and it causes real poisonings: dizziness, vomiting, a slow heart and low blood pressure. The German Federal Institute for Risk Assessment also found measurable grayanotoxins in 30 per cent of Italian alpine rhododendron honeys analysed in 2017–2019, at up to 0.10 mg/kg, and advises against eating rhododendron honeys, especially from the Black Sea region. People with heart disease on blood-pressure medication appear more susceptible.

What about foxglove?

Foxglove is seriously toxic to people and animals, and it is a question people ask about honey. It is not a honey source. Its flower tube is far too deep for a honey bee's tongue, and it is worked almost entirely by long-tongued bumblebees. HoneyHQ has found no documented poisoning from foxglove in honey, and there is no mechanism by which a honey bee colony would gather it in quantity.