Weekly cannabis use has little to no negative impact on physical health for young adults, according to a new study recently published in the Drug and Alcohol Dependence journal.

The impact of regular cannabis use on physical and mental health has been hotly debated among medical researchers, politicians, and the media. At the height of the War on Drugs, several federally-sponsored studies claimed that regular weed smoking led to poor mental and physical health. But over the past two decades, researchers have debunked many infamous “reefer madness” myths and discovered that cannabis users are generally healthier and happier than non-users.

To further explore the relationship between regular pot use and physical health, researchers from the University of Colorado Boulder compared the health and smoking patterns of twins. The study authors collected this data from the Colorado Adoption/Twin Study of Lifespan Behavioral Development and Cognitive Aging (CATSLife), an ongoing study which is tracking 308 pairs of twins from infancy into adulthood.

At the time of the present study, all subjects were between the ages of 25 to 35. The CATSLife study asked each twin to report how often they used cannabis, tobacco, and other drugs, whether they exercised recently, and if they suffered any health issues. Subjects also received a series of regular health assessments, including blood pressure, heart rate, and pulmonary function. 

Twin studies are especially useful because they allow researchers to control for genetics, family history, and other confounding factors that come into play when comparing unrelated subjects. This data allowed researchers to study between-family effects, comparing one pair of twins to another, or within-family effects, comparing one twin directly with their sibling. And as an additional comparison, researchers explored the interaction between tobacco use and physical health among the twins.

“We examined whether cannabis frequency is associated with physical health outcomes phenotypically and after controlling for shared genetic and environmental factors via a longitudinal co-twin control design,” explained lead study author Jessica Megan Ross to PsyPost. “In general, the results of this study do not support a causal association between using cannabis once a week (the mean cannabis frequency of the sample in adulthood) and detrimental physical health effects of individuals aged 25-35.”

“Our study included 25 different physical health outcomes like anthropometrics (e.g., body mass index), pulmonary function, cardiovascular function (blood pressure, heart rate), hand grip, chronic pain frequency, and diet,” Ross added. “In addition, the results for cannabis use contrast markedly with those for tobacco use in the current study, which were consistently associated with worse physical health.”

Indeed, researchers observed serious health complications in twins that used tobacco regularly. In contrast, the study reports that weekly cannabis use was not associated with poorer cardiovascular, pulmonary, or anthropometric health. Looking at the within-twin effects, researchers did find that more frequent cannabis use among pairs of identical twins was associated with a lower resting heart rate, though, which may suggest a causal effect. 

Ross also cautioned that because the study only explored young adults, the same findings may not hold true for adolescents or older adults. More frequent cannabis use may also increase the risk of negative health outcomes, but further research would be needed to confirm whether or not this is actually the case.