Canadian researchers have traced the origins of the opioid crisis to one letter published almost 40 years ago.

The letter, which said opioids were not addictive, was published in the New England Journal of Medicine (NEJM) in 1980.

Dr David Juurlink says the journal's prestige helped fuel the misguided belief that opioids were safe.

His research found that the letter was cited more than 600 times, usually to argue that opioids were not addictive.

On Wednesday, the NEJM published Dr Juurlink's rebuttal to the 1980 letter, along with his team's analysis of the number of times the letter was cited by other researchers.