© Wikimedia CommonsBust of a young Alexander the Great from the Hellenistic era, British Museum.
National Poisons Centre toxicologist Dr Leo Schep thinks the culprit could be poisonous wine made from an innocuous-looking plant.
Classical scholars have been deeply divided about what killed the Ancient Greek leader, who built a massive empire before his death, aged 32, in June of 323BC. Some accounts say he died of natural causes but others suggested members of his inner circle conspired to poison him at a celebratory banquet.
Dr Schep, who has been researching the toxicological evidence for a decade, said some of the poisoning theories - including arsenic and strychnine - were laughable.
Death would have come far too fast, he said.
His research, co-authored by Otago University classics expert Dr Pat Wheatley and published in the medical journal Clinical Toxicology, found the most plausible culprit was Veratrum album, known as white hellebore.
The white-flowered plant, which can be fermented into a poisonous wine, was well-known to the Greeks as a herbal treatment for inducing vomiting. Crucially, it could have accounted for the 12 torturous days that Alexander took to die, speechless and unable to walk. Other suggested poisons - including hemlock, aconite, wormwood, henbane and autumn crocus - would likely have killed him far more quickly.
Dr Schep began looking into the mystery in 2003 when he was approached by a company working on a BBC documentary.
"They asked me to look into it for them and I said, 'Oh yeah, I'll give it a go, I like a challenge' - thinking I wasn't going to find anything. And to my utter surprise, and their surprise, we found something that could fit the bill."
Dr Schep's theory was that Veratrum album could have been fermented as a wine that was given to the leader. It would have tasted "very bitter" but it could have been sweetened with wine - and Alexander was likely to have been very drunk at the banquet.
But whether Alexander was poisoned is still a mystery. "We'll never know really ..."
Inferring the intent could have been to hurt, not kill?