Using Cannabis With Tobacco May Not Be Worse Than Tobacco Smoking Alone

Cigarette smoking is associated with reduced airflow in young adults with or without cannabis use, and cannabis use has no consistent association in young adults related to lung function with or without cigarette smoking, according to study findings published in Respiratory Medicine.

Researchers assessed the association between lung function and cigarette smoking, cannabis use, and co-use of both substances in young adults.

Investigators analyzed data on the children of pregnant women who took part in a longitudinal prospective cohort study, enrolling in the study in the early 1980s. Of the 7223 individuals in this study’s birth cohort, 3805 (52.7%) responded to interview questions at 21 years of age; of these respondents, 2601 also received a spirometry assessment at that time measuring forced vital capacity (FVC), forced expiratory volume in 1 second (FEV₁), and ratio of FEV₁ to forced vital capacity (FVC). At age 30, a total of 2900 (40.0%) individuals from the birth cohort responded to interview questions, and 1713 received of these respondents underwent spirometry assessment. Overall, 1173 individuals completed interviews and spirometry at 21 and 30 years of age. Investigators noted some respondents completed the interview but did not participate in the spirometry, and some completed the spirometry but not all of the interview.

Investigators used the cohort with data available at both assessments for comparisons of tobacco and cannabis use. For assessment of combined use of tobacco and cannabis, they used only data from the 30 year-old cohort. The researchers conducted analyses of variance and covariance to assess associations between tobacco and cannabis use and lung function at 30 years, adjusting for physical activity score, education, body mass index, and potential confounders at 30 years. For continuing use of tobacco and cannabis, adjustments were also made for lung function at 21 years, cannabis use (adjusted for cigarette smoking), and tobacco use (adjusted for cannabis use). Sensitivity analyses showed similar results consistent with those of analyses of variance and covariance.

Data on cigarette smoking and cannabis use was dependent on participants’ responses to the question of how many cigarettes they smoked per day in the last week at ages 21 and 30. At age 21, participants were asked how often they used cannabis in the last month, whether they used cannabis but not within the last month, or whether they had never used cannabis. At age 30, they were asked if they used cannabis within the last 12 months and how much they used on those days.

Investigators noted 34.8% of all respondents smoked cigarettes at 21 years of age and 23.1% at 30 years of age, and that 17.8% smoked cigarettes at both 21 and 30 years. Of those smoking cigarettes at 21 years, 53.8% were smoking at 30 years.

There were 21.7% of respondents using cannabis at 21 years of age vs 16.9% at 30 years of age, with 9.7% using cannabis at both 21 and 30 years. Of those using cannabis at 21 years, 49.1% were using cannabis at 30 years.

Researchers evaluated participants’ lung function measures based on Global Lung Initiative (GLI) Criteria, taking into account age, gender, and height. The analysis of data collected at the 30-year follow-up indicated that participants’ lung function values were about 10% below what was expected based on GLI Criteria. Investigators found that cigarette smoking was associated with reduced airflow, with or without cannabis use. They found no consistent association between cannabis use and measures of lung function. Co-use of tobacco and cannabis revealed no additional risk to lung function beyond risks associated with tobacco use alone.

Study limitations include using a relatively short 9-year study span to characterize a lifetime of usage, potential inaccuracy of cannabis use data, unaccounted-for effects of heavier cannabis use and the changing composition of cannabis over time, a lack of data on how cannabis was consumed, nonresponse bias given the many cohort members lost to follow-up, and memory bias of self-reported values.

Investigators stated that “Our findings are consistent in suggesting impairments in lung function (early age of airflow impairment) associated with cigarette smoking.” They added that “Our findings regarding cannabis use are suggestive of few if any harms associated with relatively low levels of cannabis use evident in a young adult sample.” They concluded that co-use of tobacco smoking and cannabis is not associated with risks greater than the use of tobacco smoking alone.

This article originally appeared on Pulmonology Advisor