Plants are rich and varied sources of chemicals that change brain function, so-called psychoactive chemicals. For example, the coca plant, a shrub indigenous to the foothills of the Andes, was used for thousands of years by the local people because of the effects of the cocaine contained in the leaves. The peyote cactus has been used for millennia by the inhabitants of Mexico and Central America to experience the psychoactive effects of mescaline. In the 19th century, many families living in the Fens in the East of England grew a stand of white poppies in a corner of their garden. These were harvested to make a “poppy-head tea” containing small amounts of opium. The tea was used as a traditional remedy for the various ailments that afflicted rural life in that part of the UK.
These are just three examples but they illustrate the ingenuity of humans for finding plants that have interesting or useful properties when consumed. For every flower or plant, someone, somewhere will have tried eating it or smoking it and, if they survived, they will have reported the effects.
I was, therefore, more than surprised when, last month, I read a Guardian leader “In praise of hydrangeas” which not only extolled the plant for its blooms but also pointed out the recent discovery of the psychoactive properties of the flowers. According to a companion piece there had been a spate of hydrangea attacks in northern France, attributed, so the article alleged, to people wishing to smoke the dried flowers and leaves because of the hallucinogenic and euphoria-inducing effects which are similar to those of cannabis. The thieves must be after the new shoots judging from the state of a hydrangea in my garden; it has plenty of new growth but the few flowers left are dry, brown and rather mangy.
I hadn’t heard of the psychoactive properties of hydrangea before and didn’t know quite what to make of the story. It sounded worthy of April Fool’s Day but in fact the craze for smoking hydrangea is not new and springtime hydrangea theft has been known in Bavaria for more than 10 years. In Romania, they are so concerned that they have stopped planting the shrub in parks.
Hydrangea does not feature in my pharmacognosy textbook suggesting that if hydrangea does possess any interesting pharmacological properties, these have been overlooked. Nevertheless, the shrub does contain some unique chemicals including the coumarins, hydrangine and hydrangenol but unfortunately no psychoactive properties have been reported for these substances. Importantly, hydrangea does not contain compounds typical of cannabis such as tetrahydrocannabinol.
So what’s going on here? It doesn’t look as though there are major psychoactive chemicals in hydrangea so how does smoking the shrub produce a high? Perhaps we can get a clue from veterinary reports on the dangers of hydrangea to pets. Apparently dogs and cats can become unwell if they eat the leaves. This is attributed to chemicals found in hydrangea called cyanogenic glycosides which can break down, when metabolised, to produce the very poisonous substance, hydrogen cyanide. Cyanogenic glycosides are found in many different plants including some apricot kernels and almonds, also apple and cherry seeds.
Hydrogen cyanide is very poisonous to humans as it inhibits energy production in cells. Some of the short term effects of cyanide are headache, dizziness and confusion. Perhaps when leaves or flowers of hydrangea are smoked, small amounts of hydrogen cyanide are released. Consumption of one hydrangea joint might, therefore, provide a little cyanide and the effect, combined with a good dose of imagination could be interpreted as cannabis-like. This would also fit with the many warnings about not smoking more than one hydrangea joint because of the significant risk of cyanide poisoning.
I have not come across any reports of hydrangea smoking in the UK but I did find a report of bloom theft in Hastings and Bexhill in 2012. Apparently, the thieves were then selling the dried blooms to flower arrangers at a boot fair. At least that’s what they said!
I should like to thank Dr Ben Whalley (University of Reading) and Prof Kurt Hostettman (University of Geneva) for helpful discussions.