High levels of toxic metals discovered in blood and urine of marijuana users

NEW YORK — Is marijuana leaving behind a toxic calling card in users? Researchers from Columbia University Mailman School of Health are the first to report finding high levels of metals in the blood and urine of marijuana users. The findings demonstrate that marijuana may be a source of lead and cadmium poisoning that flies under the radar.

Marijuana is the third most commonly used drug in the world, following tobacco and alcohol. As of 2022, 21 states and Washington D.C., have legalized recreational use of marijuana, while medical marijuana is legal in 38 states and the District of Columbia. It remains federally illegal. As a result, there is very little regulation regarding contaminants, and there isn’t any guidance from federal agencies such as the U.S. Food and Drug Administration.

“Because the cannabis plant is a known scavenger of metals, we had hypothesized that individuals who use marijuana will have higher metal biomarker levels compared to those who do not use,” says study first author Katelyn McGraw, a postdoctoral researcher in Columbia Public Health’s Department of Environmental Health Sciences, in a university release. “Our results therefore indicate marijuana is a source of cadmium and lead exposure.”

McGraw and the team combined data from the National Health and Nutrition Examination Survey (NHANES) from between 2005 and 2018 and classified 7,254 survey participants by use: non-marijuana/non-tobacco, exclusive marijuana, exclusive tobacco, and dual marijuana and tobacco use. They measured levels of five metals in blood and 16 in urine.

Researchers also used the following four NHANES variables to define exclusive marijuana and tobacco use: current cigarette smoking, serum cotinine levels, self-reported marijuana use, and recent marijuana use. Exclusive tobacco use included individuals who either answered yes to “Do you now smoke cigarettes,” or if individuals had a serum cotinine level >10ng/mL. Cotinine is found in tobacco and is the main nicotine metabolite.

The team found that those exclusively using marijuana had much higher lead levels of metal in both their blood and urine (1.27 ug/dL and 1.21 ug/g creatinine, respectively). This is possibly the largest study to date linking marijuana use to metal exposure in the body. Previously, studies have looked at the heavy metals in the plant itself. This work now indicates that there is a potential public health threat from using this increasingly legal drug.

“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,” says senior author Tiffany R Sanchez, PhD, assistant professor of environmental health sciences at Columbia Public Health.

The findings are published in the journal Environmental Health Perspectives.

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