Research news: February 2012
Light social use of marijuana does no discernible harm to users’ lungs, according to a large cohort study from the US. More than 5000 young adults joined the study in 1985 and answered regular questions about use of tobacco and marijuana for the next 20 years. They also had five sets of pulmonary function tests. If anything, light smoking of marijuana was associated with improved lung function, particularly a higher forced vital capacity (FVC). The link with FVC has been noticed before, say the authors, who suspect some kind of training effect from repeated deep inhalations.
The authors used “joint years” to measure lifetime exposure, where one joint year means one joint a day for one year or 365 joints. Among adults with low lifetime exposure (two joint years), each joint year was associated with an extra 13 mL (95% CI 6.4 to 20) of forced expiratory volume in