Cannabis is a hyperaccumulator, a class of more than 700 plants that accumulate metals from soil, water and fertilizers at levels far greater than average, often hundreds or thousands of times more than other plants.  To investigate the amount of metals in the blood and urine of cannabis users, researchers analyzed data from 2005 to 2018 representing 7,254 participants who reported on their diet, health, demographics and drug use, while providing single blood and urine samples. Researchers could not tell what kind of cannabis these individuals used, where it was sourced from or where participants lived, though they adjusted for other factors that can affect exposure to and excretion of metals (namely race/ethnicity, age, sex, education, and seafood consumption).

The study found that cannabis-only users had 27% high blood lead levels and 21% more lead in their urine when compared to non-users of tobacco and cannabis. They also had higher levels of cadmium — 22% more in their blood than non-users. Lead and cadmium can cause long-term health damage, like cardiovascular disease, chronic obstructive pulmonary disease, cognitive impairments and increase the risk of cancer.  In regulated cannabis markets where products are tested, any cannabis that fails must be destroyed or remediated, with legal cannabis states often issuing recalls for any products that fail and mistakenly hit store shelves.

None of the other 15 elements researchers evaluated — like arsenic, cobalt, manganese and mercury — has a clear causal association with cannabis use, though tobacco users saw much higher levels.  Urinary cadmium levels among tobacco users were three times higher than those of cannabis-only users and their blood lead levels were 26% higher. The study also found that tobacco use was associated with higher levels of antimony, barium, tungsten and uranium.  In general, regulated cannabis undergoes more intense testing than tobacco, and previous studies have long documented the heavy metal content in cigarette smoke.

“To the best of our knowledge, this is the largest known study on biomarkers of metal exposure in participants who exclusively use marijuana in a representative population of U.S. adults,” authors noted. The study findings reinforce that regulated, legal cannabis provides for more consumer safety, as illicit cannabis does not undergo this same testing. Authors note that the study was limited by its small sample of exclusive cannabis users, along with its inability to hone in on the type of product used (i.

e. vapes, combustibles and edibles) which kept researchers from determining the difference in metal concentrations by product. Given that the data was taken from 2005 to 2018, it’s also uncertain how much cannabis was obtained through the legal or illicit markets — though it’s likely that most was illicit use, as the first states to legalize cannabis only began in 2014 and adult-use legalization was still limited in the years that followed. “We found overall associations between internal metal levels and exclusive marijuana use, highlighting the relevance of marijuana for metal exposure and the importance of follow-up studies to identify the long-term implications of these exposures,” researchers stated.

  “Future investigations of cannabis contaminants must assess other contaminants of concern and potential health effects to inform regulatory, industry and other key stakeholders, to safeguard public health and address safety concerns related to the growing use of cannabis in the United States.” Read less