Nigel Mentzel, 70, turned to mind-bending synthetic drugs after retiring as a council planner.
The keep-fit fanatic began smoking a ‘legal high’ called Cherry Bomb on a daily basis.
Nigel, a keen blues guitarist, bought huge amounts of the drug from a shop in Cardiff.
But an inquest into his death was told the ‘legal high’ brought about a dramatic change in his behaviour.
His partner said Nigel, one of Britain’s top experts in psychedelic art, became “defensive and angry”.
He collapsed and died at his home in January with traces of synthetic cannabinoids in his system.
A pathologist’s report said Nigel died from “sudden death associated with use of synthetic cannabinoids”.
The inquest heard the so-called ‘legal high’ was in fact more dangerous than cannabis – a banned class B drug.