A new study has found that people who exclusively use marijuana have higher levels of potentially dangerous metals in their blood and urine than those who don’t. The findings suggest that marijuana may be an overlooked source of metal exposure, an important consideration given the rise in its use.
After tobacco and alcohol, marijuana is the most commonly used drug in the world. The terms ‘marijuana’ and ‘cannabis’ are often used interchangeably, but whereas cannabis describes cannabis products in general, marijuana specifically refers to cannabis products that are made from dried flowers, leaves, stems and seeds of the cannabis plant.
In the US, while some states and Washington DC have legalized recreational marijuana use, the drug is still illegal at the federal level, meaning that the regulation of contaminants in cannabis-containing products remains haphazard. This presents a potential issue, given that the cannabis plant is known to accumulate metals found in water, soil, fertilizers and pesticides.
Researchers from the Columbia University Mailman School of Public Health undertook a study to examine just how much metal makes its way from the plant to the body of marijuana users.
“Because the cannabis plant is a known scavenger of metals, we had hypothesized that individuals who use marijuana will have higher biomarker levels compared to those who do not use,” said Katelyn McGraw, the study’s lead author. “Our results therefore indicate marijuana is a source of cadmium and lead exposure.”
Using data from the National Health and Nutrition Examination Survey (NHANES) for the years 2005 to 2018, the researchers classified 7,254 participants by their marijuana use: non-marijuana/non-tobacco, exclusively marijuana, exclusively tobacco, and dual marijuana and tobacco use. Five metals were measured in the blood and 16 in the urine.
Four variables were used to define exclusive marijuana and tobacco use: current cigarette smoking, serum cotinine levels, self-reported marijuana use and recent marijuana use. Serum cotinine levels reflect recent exposure to nicotine in tobacco smoke.
After adjusting for age, sex, race and ethnicity and education, the researchers found higher levels of cadmium and lead in the blood and urine of participants reporting exclusive marijuana use when compared with non-marijuana/non-tobacco use. Cadmium and lead levels were also higher in exclusive marijuana users who’d reported using the drug within the last seven days, with metal levels falling with increased time since last use.
Cadmium biomarkers levels were higher in exclusive tobacco uses compared with exclusive marijuana users, which the researchers put down to either differences in frequency of use or differences in cadmium levels in the tobacco or cannabis plants themselves. Dual marijuana and tobacco users also had higher cadmium and lead levels compared to non-marijuana/non-tobacco users.
The researchers say that, taken together, these results suggest that marijuana use is an important and under-recognized source of cadmium and lead exposure, independent of tobacco use, that may contribute to health issues in chronic marijuana users.
Cadmium is excreted from the body in urine, but it’s excreted slowly meaning it can accumulate over time. Studies have associated a buildup of cadmium with kidney disease and fragile bones. It’s also considered to be carcinogenic. Long-term exposure to lead may cause weakness in the extremities, headaches, fatigue, and damaged nerve and renal function.
In terms of limitations, the researchers recognize that their study did not include how the marijuana was used, such as vape, combustibles and edibles, so they were unable to determine the difference in metal concentrations by method of use.
“Going forward, research on cannabis use and cannabis contaminants, particularly metals, should be conducted to address public health concerns related to the growing number of cannabis users,” said Tiffany Sanchez, corresponding author of the study.
The study was published in the journal Environmental Health Perspectives.