Elevated Blood and Urine Metal Levels in Marijuana Users

Cannabis usage may be a substantial and underappreciated source of lead and cadmium exposure, according to researchers who found large quantities of metals in the blood and urine of marijuana users.

The study, conducted at Columbia University's Mailman School of Public Health and published online in the journal Environmental Health Perspectives, is among the first to report biomarker metal levels in marijuana users.

The National Health and Nutrition Examination Survey data for the years 2005 to 2018 was merged by the researchers.

A biennial research program led by the National Center for Health Statistics (NCHS) at the CDC, NCHS NHANES, is intended to evaluate adults' and children's health and nutritional status in the United States.

Participants who reported using marijuana exclusively had lead levels in their blood and urine that were noticeably higher than those who did not use marijuana or cigarettes (1.27 ug/dL and 1.21 ug/g creatinine, respectively).

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.

-First author Katelyn McGraw

She continues that the findings suggest that marijuana is a cause of lead and cadmium exposure.

How was the study conducted?

The 7,254 survey respondents were divided into four groups by usage by McGraw and colleagues:

  • Non-marijuana/non-tobacco
  • Exclusive marijuana
  • Exclusive tobacco
  • Dual marijuana and tobacco use.

The blood contained five metals, but the urine included sixteen.

The researchers looked at four NHANES variables, including current cigarette smoking, serum cotinine levels, self-reported marijuana use, and recent marijuana use, to determine who exclusively used marijuana and cigarettes.

Individuals were considered to have exclusively used tobacco if they checked the "Do you currently smoke" box or if their blood cotinine level was greater than 10 ng/mL.

Behind alcohol and cigarettes, marijuana is the third most widely consumed narcotic worldwide. By 2022, recreational marijuana use was permitted in 21 states and Washington, D.C., accounting for more than half of the country's population; medicinal marijuana use will be permitted in 38 states and Washington, D.C.

The FDA, the EPA, and other federal regulatory bodies have not provided any guidelines about regulating pollutants in any cannabis-containing goods due to marijuana's continued federal criminalization.

48.2 million Americans, or 18% of the population, reported consuming marijuana at least once in the previous year as of 2019. Although inorganic arsenic, cadmium, lead, and total mercury amounts in marijuana products are regulated in 28 states, the regulation levels differ depending on the metal and the state.

Senior author Tiffany R. Sanchez says: "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."


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