Warning: Columbia University Uncovers High Metal Levels in Blood of Marijuana Users

Marijuana Illness Concept

A recent study discovered significant levels of metals in the blood and urine of marijuana users, indicating marijuana as a possible unrecognized source of lead and cadmium exposure. This research, among the first to link self-reported marijuana use with internal metal exposure, raises concerns about public health, especially as marijuana consumption rises and federal regulations remain inconsistent.

A Columbia University study found high metal levels in marijuana users’ blood and urine, highlighting potential health risks and emphasizing the need for consistent regulations.

Research recently conducted at Columbia University Mailman School of Public Health detected significant levels of metals in the blood and urine among marijuana users. The results suggest that marijuana may be an important and under-recognized source of lead and cadmium exposure.

This is among the first studies to report biomarker metal levels among marijuana users and most likely the largest study to date, that links self-reported marijuana use to internal measures of metal exposure, rather than just looking at metal levels in the cannabis plant. The results were published on August 30 in the journal Environmental Health Perspectives.

Key Findings

Measurements reported by participants for exclusive marijuana use compared to nonmarijuana-tobacco had significantly higher lead levels in blood (1.27 ug/dL) and urine (1.21 ug/g creatinine). 

“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,” said Katelyn McGraw, postdoctoral researcher in Columbia Public Health’s Department of Environmental Health Sciences, and the first author. “Our results therefore indicate marijuana is a source of cadmium and lead exposure.”

Research Methodology

The researchers combined data from the National Health and Nutrition Examination Survey for the years 2005-2018). Led by the National Center for Health Statistics (NCHS) at the CDC, NCHS NHANES is a biannual program of studies designed to assess the health and nutritional status of adults and children in the U.S.

McGraw and colleagues classified the 7,254 survey participants by use: non-marijuana/non-tobacco, exclusive marijuana, exclusive tobacco, and dual marijuana and tobacco use. Five metals were measured in the blood and 16 in urine.

The researchers used four NHANES variables to define exclusive marijuana and tobacco use: current cigarette smoking, serum cotinine levels, self-reported ever marijuana use, and recent marijuana use. Exclusive tobacco use was defined as individuals who either answered yes to ‘do you now smoke cigarettes, or if individuals had a serum cotinine level >10ng/mL.

Marijuana’s Prevalence and Regulation

Marijuana is the third most commonly used drug in the world behind tobacco and alcohol. As of 2022, 21 states and Washington D.C., covering more than 50 percent of the U.S. population, have legalized recreational use of marijuana; and medical marijuana is legal in 38 states and Washington D.C. However, because marijuana is still illegal at the federal level, regulation of contaminants in all cannabis-containing products remains piecemeal and there has been no guidance from federal regulatory agencies like the FDA or EPA. As of 2019, 48.2 million people, or 18 percent of Americans, report using marijuana at least once in the last year.

While 28 states regulate inorganic arsenic, cadmium, lead, and total mercury concentrations in marijuana products, regulation limits vary by metal and by state. 

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

Reference: “Blood and Urinary Metal Levels among Exclusive Marijuana Users in NHANES (2005–2018)” by Katlyn E. McGraw, Anne E. Nigra, Joshua Klett, Marisa Sobel, Elizabeth C. Oelsner, Ana Navas-Acien, Xin Hu and Tiffany R. Sanchez, 30 August 2023, Environmental Health Perspectives.
DOI: 10.1289/EHP12074

Co-authors are Anne E. Nigra, Joshua Klett, Marisa Sobel, and Ana Navas-Acien, Columbia Public Health; Elizabeth C. Oelsner, Columbia University Irving Medical Center; and Xin Hu, Emory University School of Medicine.

The study was supported by the National Institutes of Health (NIH) National Institute of Environmental Health grants P30ES009089 and T32ES007322.

10 Comments on "Warning: Columbia University Uncovers High Metal Levels in Blood of Marijuana Users"

  1. So where is the lead and cadmium coming from? Should we water our pot plans with better water?

  2. We stop looking at the benefits?

  3. The level of lead in the blood discussed in this WORTHLESS article is 1.27 ug/dL, which is ONE FOURTH of the amount 5 µg/dL that the CDC consideres “cause for concern.”

    The headline for the SHAMELESS article should be “NO CAUSE FOR CONCERN” about levels of lead in the blood of marijuana smokers.

    Meanwhile Columbia University should be ASHAMED to employ the hacks who made this DECEPTIVE mess.

  4. More anti-marijuana drug war propaganda. It calls into question as to the competence and credibility of the “SO-CALLED” scientists doing the “SO-CALLED’research. These statements are way out of proportion and context as well. Many of these studies are outright lies and completely contradictory to the facts. Most of which are funded and directed by the biased and poorly educated propagandists within the government.

  5. NOTE ON CREDIBILITY. The above funding was provided by The Federal Government which has a very strict bias against any pro marijuana research. Bias to the point of refusing grant funding. I will never again except any research findings by this quasi- government origination. I find no credibility with this organization who seem more interested in acquiring grant funding that finding valid facts. I suspected just more pro-drug war propaganda.

  6. Reporters should be ashamed of themselves for spreading this misinformation, it’s all more propaganda to stoke the fears of bigots. It is largely due to racism that cannabis was banned(you can learn that in college textbooks) once upon a time they claimed that Mexicans were crossing the border smoking cannabis and committing violent crimes they said that Hindus were spreading it in California and black people were intermingling with other races as a result of cannabis use, but it was all federal propaganda to turn the citizens against cannabis, which BTW was used to create parachute cords uniforms ect. During WW2 our founding fathers supported cannabis hemp, Washington swore by it, and Jefferson wrote about cultivation techniques for cannabis hemp.

  7. Where is the break in the data between field-grown and hydroponically grown? No one adds those metals to hydro-grow, so they’re coming from somewhere else. Did anyone do a spectrographic analysis of the rolling papers? Paper is known to occasionally be treated with dioxins and other chemicals… Sorry; this is just weak. The conclusions announced in the headlines as are not justified. _POOR SCIENCE_ makes everyone else look bad.

  8. Hi everyone, this is the fault of anti-drug policies that didn’t allow for any research into pot use, and we’re only now catching up to 40 years of what should be safety research.

    Pot is known to suck up and concentrate these metals direct from the soil. It’s just what it does.

    As the study and the article says, this is step 1 – finding the problem. We still need to know just how big the issue is (we want ppl smoking to be as safe as possible) and where the heavy metal comes from. Like another poster said, it could even be the rolling paper. But that’s not the point of this study – this is to show the problem exists, period.

    In the end, there needs to be safety mandates and legal requirements for all users to be safe. That’s where the demand should be.

  9. The studies were done in the most polluted state in the country. Do the subjects live in NY? Did their cannabis come from NY? Was it grown outdoors? Are they smoking out of metal pipes? Not enough info.. this seems like anti-cannabis propaganda.

  10. Check the link to the actual study. This result is completely biased. Tobacco causes the biggest concentrations of metals. There was almost no difference between marijuana users and those who smoked nothing.

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