The controversy with marijuana is only likely to continue as research studies try to understand if marijuana use is associated with an increased risk of cancer. While research has made clear the link between tobacco cigarettes and certain kinds of cancer, there is still ambiguity in regards to the carcinogenic effects that smoking a joint could have. Now new research published in JAMA Network Open has taken a meta-analysis approach to try to understand once and for all if smoking marijuana is associated with increased cancer risk.
The research comes from the Northern California Institute of Research and Education in San Francisco in collaboration with other institutions. As recreational use of marijuana becomes more and more popular (more than one in seven adults reported that they used marijuana in 2017), and the industry skyrockets around the country, the researchers wanted to look closely at the bigger picture of the health concerns that smoking a joint could cause.
In their investigations, the authors commented that both marijuana joints and tobacco cigarettes have many of the same substances – substances that are potentially carcinogenic. "Marijuana smoke and tobacco smoke share carcinogens, including toxic gases, reactive oxygen species, and polycyclic aromatic hydrocarbons, such as benzo[alpha]pyrene and phenols, which are 20 times higher in unfiltered marijuana than in cigarette smoke," write the authors. "Given that cancer is the second leading cause of death in the United States and smoking remains the largest preventable cause of cancer death (responsible for 28.6% of all cancer deaths in 2014), similar toxic effects of marijuana smoke and tobacco smoke may have important health implications.”
In conducting their analysis, the researchers, led by first author Dr. Mehrnaz Ghasemiesfe, reviewed 25 different studies that all focused on the association between marijuana and cancer risk. The types of cancer investigated in the studies included lung cancer, head and neck cancers, and urogenital cancers, among several others.
For each kind of cancer, the authors observed different strengths of association; however, none was particularly strong. For example, they did not find an association between long-term use of marijuana (defined here as smoking a joint a day for a year) and head and neck cancers, although the researchers note that for marijuana users who smoke more heavily, there were mixed results in terms of increased cancer risk. They were not able to conclude an increased risk for lung cancer and similarly there was not enough evidence to show an increased risk for nasopharyngeal carcinoma, oral cancer, laryngeal, pharyngeal, esophageal, prostate, cervical, penile, or colorectal cancers. The only cancers that were found to have an increased risk for long-time users of marijuana (10+ years) were urogenital cancers, but even this association was weak.
Nevertheless, the authors caution that these findings may not reflect the whole picture due to data constraints from the studies they analyzed. They urge that continued investigation into this topic is imperative.
"Misinformation [on this topic] may constitute an additional threat to public health; cannabis is being increasingly marketed as a potential cure for cancer in the absence of evidence, with enormous engagement in this misinformation on social media, particularly in states that have legalized recreational use. As marijuana smoking and other forms of marijuana use increase and evolve, it will be critical to develop a better understanding of the association of these different use behaviors with the development of cancers and other chronic conditions and to ensure accurate messaging to the public.”