A Canadian doctor says a one paragraph letter in a prestigious medical journal was part of a push to convince physicians to prescribe opioids more freely by downplaying addiction risks.

The 1980 letter to the editor in the New England Journal of Medicine was titled, "Addiction Rare in Patients Treated With Narcotic."

But the content of the letter itself doesn't justify the title, said Dr. David Juurlink, head of clinical pharmacology and toxicology at Toronto's Sunnybrook Health Sciences Centre.

In a correspondence published in Wednesday's issue of the same journal, Juurlink and his co-authors analyzed more than 600 published references or citations to the letter up until March 30 of this year.  

"We had a suspicion that given the number of times this rather meagre publication has been cited that many of the citation would've been trumpeting the message in its title," said Juurlink. "Sure enough, that's what we found. Nearly three-quarters of the citing articles parroted that study's message that addiction was rare, based on nothing on all."

A graph showing the number and type of citations illustrates how positive citations rose in the mid 1990s. It coincided with a push to prescribe opioids much more liberally.

The 101-word letter by Dr. Hershel Jick and Jane Porter, a grad student at the time, at Boston University Medical Center focused on addiction risk to opioid prescriptions among patients at their hospital. But it lacked details of a true study, such as clear objectives and methods describing how addiction was ascertained.

"This has absolutely no applicability to outpatients with chronic pain. That did not stop the thought leaders in the field of pain or the drug companies who were paying them from promulgating the message," Juurlink said.

Juurlink recalls in journalist Sam Quinones's 2015 book Dreamland how Jick never intended for his short-term observations to be applied to outpatients taking opioids over a long period of time. 

 "I'm essentially mortified that that letter to the editor was used as an excuse to do what these drug companies did," Jick told The Associated Press in an interview on Wednesday. "They used this letter to spread the word that these drugs were not very addictive."

Jick also said he testified as a government witness in a lawsuit years ago over the marketing of pain drugs.

A YouTube video from Physicians for Responsible Opioid Prescribing titled "Long-term opioid therapy reconsidered: addiction is not rare in pain patients" describes how those campaigns to physicians were mounted and the resulting crisis two decades later.  

The 1980 letter received vastly disproportionate attention. The team from Sunnybrook and the Institute for Clinical Evaluative Sciences found similar research letters published in the same journal over that period were cited an average of 11 times.

In their article, the researchers said they believe "this citation pattern contributed to the North American opioid crisis by helping to shape a narrative that allayed prescribers' concerns about the risk of addiction associated with long-term opioid therapy."

In 2007, the manufacturer of OxyContin and three senior executives pleaded guilty in the U.S. to federal criminal charges that they misled regulators, doctors, and patients about the risk of addiction associated with the drug.

Juurlink suspects that carelessness also contributed to the 608 citations among those who hadn't read beyond the title of the letter.

The risk of addiction from opioids in the real world isn't known.

"The best available evidence suggests it's somewhere between five and 10 per cent with long-term therapy, which is a staggering number when you think about the millions of people who are on these drugs now."

While there were also citations that negated the letter's conclusion about addictive opioids over the study period, this year is the first where critiques are more common than affirming articles.   

With files from Associated Press