As the march toward legalization of Marijuana use continues amidst ongoing debate, more attention has been paid to the impacts of Cannabis use on overall health. Although a growing body of evidence exists regarding the harmful effects of Cannabis use, its effects on cardiovascular health remain a topic of ongoing debate. High levels of evidence such as meta-analyses have identified smoking Cannabis as a high-ranking trigger for heart attack. However, other robust levels of evidence point to an opposing conclusion when confounding variables are adjusted for, such as alcohol use.
A recent Mendelian Randomization study evaluated genetically determined Cannabis use and the risk of cardiovascular diseases. This study has advantages over previous studies, including the study design itself, which helps overcome limitations of prior observations by adjusting for confounding variables. For example, researchers found that when certain variables such as tobacco use and body mass index were accounted for, Cannabis use was causally associated with certain cardiovascular conditions such as small vessel stroke and atrial fibrillation. In addition, a large sample size improved the statistical power of the Randomization study.
This study design also helps to adjust for reverse causation bias. Reverse causation bias occurs when a causal relationship is concluded due to an observed association between two variables. An example of this may be the observed association of low social mobility and Schizophrenia. A researcher may conclude that low social mobility causes Schizophrenia based on their observation. However, another valid explanation of an empirical relationship would be that schizophrenia causes low social mobility. Thus, further analysis would be required to suggest causality.
This study suggested that there was no causal relationship between genetic predisposition to Cannabis use and cardiovascular disease. Establishing a causal relationship is an essential goal in science, especially in epidemiologic studies. This study, therefore, represents an important contribution to the compendium of ongoing research investigating the causal relationship between Cannabis use and effects on health amid rapid legalization.
Sources: The Lancet, The American Journal of Cardiology, frontiers in Cardiovascular Medicine, ScienceDirect