A US coroner has stood by his conclusion that a woman died of an overdose of THC – the active ingredient in cannabis – after experts cast doubt on the finding.

In what would ostensibly be the first confirmed case in the country, coroner Dr Christy Montegut, of St John the Baptist Parish in Louisiana, said an unnamed 39-year-old woman died in February after vaping THC oil.

“It looked like it was all THC because her autopsy showed no physical disease or afflictions that were the cause of death. There was nothing else identified in the toxicology — no other drugs, no alcohol.

There was nothing else,” Dr Montegut told the New Orleans Advocate newspaper last month.

He added: “I’m thinking this lady must have vaped this THC oil and got a high level in her system and (it) made her stop breathing, like a respiratory failure.”

The woman’s toxicology report said she had 8.4 nanograms of the substance per millilitre of blood in her system, which Dr Montegut said was likely the result of vaping using highly concentrated THC oil.