Study finds weekly cannabis use has minimal impairment on physical health

A study published in the journal Drug and Alcohol Dependence explored the association between cannabis use and physical health among 308 sets of twins.

Research on the influence of cannabis use on cardiovascular functions, pulmonary functions, and other indicators is still growing, but one new study has shed new light on the topic. “The effects of cannabis use on physical health: A co-twin control study,” published in the journal Drug and Alcohol Dependence explored the relationship between cannabis use and physical health among 308 sets of twins, with the results suggesting that cannabis use is not associated with detrimental physical effects.

Cannabis research is still catching up to studies surrounding tobacco and alcohol’s effect on physical health, though studies so far have indicated cannabis has an impact on respiratory health, cardiovascular health, and body mass index.

The data is from an ongoing study called “Colorado Adoption/Twin Study of Lifespan Behavioral Development and Cognitive Aging,” through the University of Colorado Boulder. It is the first prospective study of cognitive aging from infancy through adulthood, with a purpose of studying “how early and current influences accumulate over one’s life to impact how well individuals build and maintain cognitive functioning,” according to the CU Boulder website.

As part of the study, researchers are tracing factors associated with decreases, maintenance or boosts in cognitive abilities. Through in-depth behavioral and health measurements, analysis of environmental settings, biomarker and genotype data, researchers are looking to assess the association of cognitive changes with possible physical and behavioral health precursors, “to trace the emergence of these associations,” researchers say on the CU Boulder site.

As part of the study, researchers are tracing factors associated with decreases, maintenance, or boosts in cognitive abilities. Through in-depth behavioral and health measurements, analysis of environmental settings, biomarker and genotype data, researchers are looking to assess the association of cognitive changes with possible physical and behavioral health precursors, “to trace the emergence of these associations,” researchers say on the CU Boulder site.

Study author Jessica Megan Ross worked with her team to better understand these effects, specifically focusing on monozygotic twins (or twins sharing 100% of their genetic makeup) and dizygotic twins (or twins sharing 50% of their genetic makeup.

Researchers are also using siblings and twins for the larger study, assessing them on a wide array of measures almost yearly from birth into their 20s. With this model, researchers were able to control shared genetic and environmental factors as they analyzed the results for the cannabis study and others.

“Understanding the impact of cannabis use on physical health is an important public health concern because the extant literature has reported mixed results,” Ross told PsyPost.

“The changes in legalization of cannabis use throughout the United States has been associated with increases in adult cannabis use. However, we still do not have a clear picture of how cannabis use impacts physical health.”

Respondents were asked to self-report how often they used cannabis, tobacco, alcohol, or other drugs during adolescence. Researchers then calculated each person’s average lifetime frequency of cannabis, calculating individuals’ average number of days in the past month they had used cannabis across the study assessments.

So, increased cannabis use in adolescence isn’t necessarily the cause of less exercise in adulthood, just as frequent cannabis use in adulthood isn’t necessarily related to more frequent appetite loss.

Researchers also looked at between-family and within-family effects; between-family effects looked at average cannabis use frequency within each twin pair and compared the averages across all the pairs, while within-family effects were measured by a twin’s deviations from the average cannabis frequency within their pair.

They found that, at the between-family level, more cannabis use in adolescence was associated with infrequent exercise as an adult; these effects weren’t present at the within-family level, suggesting that the effects were partially because of shared family factors, not cannabis use. At the within-twin level, more frequent cannabis use in adulthood was correlated with a lower resting heart rate for monozygotic twin pairs. The observation held true after controlling for family factors and other substance use, providing some evidence that cannabis use can affect the resting heart rate.

The study conclusions note, “The associations between cannabis use with exercise engagement and frequency of appetite loss are explained by familial confounding while the association between cannabis use and resting HR was not. These results do not support a causal association between cannabis use once a week and poorer physical health effects among adults aged 25–35.”

The researchers noted the study was limited in a number of ways, namely that the findings may not generalize to the greater U.S. population. Ross said that these results apply to adults using cannabis once a week on average and do not apply to adolescents and adults using cannabis more frequently.

“Although we did not find that cannabis use (once a week) is associated with detrimental physical health effects, people can still develop other negative outcomes from use like a cannabis use disorder,” Ross said.