Heavy marijuana users in adolescence and young adulthood have a higher rate of lung cancer later in life, according to a new study by a Northern Medical Program professor.
Heavy marijuana users in adolescence and young adulthood have a higher rate of lung cancer later in life, according to a new study by a Northern Medical Program professor.
In an article published Friday in the medical journal Cancer Causes Control, Dr. Russ Callaghan found that heavy pot users have a cancer rate more than twofold higher than the rest of the population four decades after they started smoking the drug.
"I was trying to frame the risk of marijuana smoking in relation to the two other legal drugs [tobacco and alcohol], which have much greater harms," Callaghan said of the study, which looked at the health outcomes of a group of Swedish men over 40 years.
The study is the first of its kind to find a cancer link with marijuana use, which Callaghan attributes to the length of time examined.
In his paper, Callaghan pointed to other types of research like animal experiments and in-vitro studies that suggested a link between marijuana smoking and cancer should exist.
Although the lung cancer rate for marijuana users was twofold higher, Callaghan's paper also found tobacco smokers had a disease rate that was fivefold higher than non users.
Callaghan authored the report along with Swedish researchers Peter Allebeck and Anna Sidorchuk.
They used data collected in 1969 and 1970 in Sweden when the Swedish army was conscripting young men and as part of the recruitment process had them complete a detailed questionnaire about their past drug use. The scientists took that data and then compared it with the medical records of those same men for the next 40 years to reach their conclusions.Because the data about marijuana use came from interviews conducted more than four decades ago, Callaghan and his coauthors were unable to determine how many of the Swedish conscripts continued using the drug later in life and how many stopped when they were still young. They also don't know how the drug was consumed, but, culturally, smoking was the most common method at the time.In the paper, Callaghan hypothesized that even smoking only at a young age could be harmful due to the sensitive nature of lung development.The findings in Callaghan's study contradict those in another long-term study conducted in California in 1997 that found no link between marijuana smoking and lung cancer. What makes his analysis different, according to Callaghan, is the length of time examined before reaching a conclusion."One of the difficulties of doing studies on cannabis use and lung cancer is that cannabis use often happens in adolescence or young adulthood, but lung cancer only develops [later], the median or average age is around 65 or 70," Callaghan said. "So there's a long period between the two variables so you need a long span of data or a long cohort study."Callaghan would like to give the American data another look, but so far researchers in that study have not replied to requests to give him access to their data.The next step for research is to have another study confirm Callaghan's results and look at the difference between sustained use over a lifetime compared with use at a young age only. Replicating the study would be difficult as the Swedish database is unique in that it asked detailed questions about drug use to a large group of men at the same time.Callaghan, who originally hails from Prince George but just recently returned to the community after accepting a job at UNBC, spent about 18 months working on the paper. He hopes his findings will help people make an informed choice before they smoke as well as enlighten the debate around marijuana legalization, which hinges on the costs and benefits of the drug use."Because the prevalence of marijuana [use] is going up among young people and it's highly used in Canada, there's a sense that cannabis is not at all harmful, it doesn't carry any risk," he said, noting his findings disprove that notion. "It's giving more information for young adults, high school students, policy makers and drug use counsellors."
