Does oleander need a health warning?

Ping! That was the sound of an e-mail arriving. It is from a friend who suggests that I write about the Mediterranean shrub oleander. He says that it is increasingly to be seen on sale in garden centres, perhaps because global warming now allows it to thrive in southern Britain, but the plant labels fail to warn that it is highly poisonous to humans and animals.

Nerium oleander is an evergreen member of the dogbane family (Apocynaceae), growing to some six metres high. It has narrow leathery leaves and clusters of pink or white flowers. It tolerates droughts, poor soil and the occasional light frost.

In Mediterranean countries it often grows wild in dry stream beds but it is also cultivated for field boundaries and as an ornamental plant. The plant contains a range of toxic constituents, including cardiac glycosides and strychnine-like compounds.

Despite its toxicity, it has found use as a medicine. Pliny the Elder — always good for a quote or two — claimed in his ‘Natural history’ (ca AD77) that it cures snakebite if taken in wine with rue.

And John Gerard’s herbal (1597), while remarking on its toxicity when taken internally, said that applied externally it could improve the digestion.

In modern times, despite warnings from the US Food and Drug Administration, some alternative medicine practitioners have recommended oleander leaves and root extracts for complaints ranging from cardiac conditions to constipation, from diabetes to dropsy, from scabies to swellings and from worms to warts.

And in orthodox medicine, one glycoside constituent, oleandrin, is currently being investigated for possible anticancer action.

But just how toxic is oleander? It seems to be generally agreed that all parts of the plant —  flowers, leaves, wood, sap, roots — are poisonous and it has been claimed that a child could die after eating a single leaf.

Even honey from the pollen is supposedly poisonous. It is also said that oleander’s poisons survive burning, so that accidentally inhaling smoke from a bonfire of prunings may be dangerous and meat cooked over a fire of oleander wood can contain poison transferred to it by the smoke.

Some of Wellington’s men in the Peninsular War of 1807–14 are said to have died after eating meat cooked on skewers made from oleander. And in 1880 it was reported that soldiers had died after sleeping on oleander branches.

The shrub is also poisonous to grazing animals, particularly to horses. Although farm animals normally avoid contact with it, it is claimed that cattle, sheep and goats can be killed by drinking water into which oleander leaves have fallen.

Some of these toxicity claims may be exaggerated, but it remains astonishing that garden centres fail to give any warnings. Can they not be compelled to do so?