Marijuana users may be building up high levels of toxic metals in their blood, a new study suggests.
According to researchers, people who use marijuana exclusively have significant levels of lead and cadmium in their bodies. These are the same toxic metals found in some cigarette smokers.
Marijuana is the world's third most commonly used drug, behind tobacco and alcohol.
"Like the tobacco plant, the cannabis plant is a hyper-accumulator of metals," said lead author Katlyn McGraw, a post-doctoral researcher at Columbia University Mailman School of Public Health in New York City. "The plant absorbs metals from the soil and then deposits them in the leaves and the stems and the buds, so when the marijuana is smoked or inhaled people might be inhaling those metals." The metals include cadmium and lead.
Low levels of cadmium have been associated with a number of adverse health effects, including heart and vascular disease. Lead, meanwhile, is a potent neurotoxin in young people and is also linked to heart disease.
"There's no safe level of lead," McGraw said.
In states where marijuana is legal, its growing conditions are regulated, but there are no nationwide standards or safeguards, and there won't be until it is legal across the United States, McGraw added.
"We need federal regulation to make sure the new products coming into the market will be regulated for contaminants, not just metals, but also pesticides, molds and other things," she said.
McGraw said consumers should be aware of the potential for exposure to toxic metals when they buy marijuana.
"Think about how much and how often you're using marijuana and that might be exposing yourself to these toxic metals, these metals that we know are bad for your health," she said.
One expert suspects heavy metal levels in marijuana would not be seen if it were legalized and its growing conditions were subject to mandatory testing.
"Cannabis and hemp are good at cleaning up soil, for example, after a toxic accident, as they suck the crap out of the ground," said Dr. Peter Grinspoon, a cannabis specialist at Massachusetts General Hospital and Harvard Medical School in Boston. "This is why a legal market is so important."
In illegal markets, lead and heavy metals in marijuana are higher than in regulated states where it is tested, he said.
"In the legal market, lead and heavy metals should be lower, if the system is working and levels are tested," Grinspoon added.
For the study, McGraw and her colleagues collected data on more than 7,200 participants in a nationwide health survey from 2005 to 2018 who used marijuana exclusively. The researchers measured the levels of five metals in participants' blood and 16 in urine.
Participants who used marijuana exclusively had significantly higher lead and cadmium levels in blood and urine than people who didn't use the drug.
Because data were self-reported, the investigators can't be sure the participants' exposure to these metals was exclusively from cannabis, only that it seems likely.
"This research builds upon other studies underscoring concerns related to harmful contaminants in cannabis," said Pat Aussem, vice president for consumer clinical content development at the Partnership to End Addiction.
"As a plant, it is subject to growing and processing conditions that can elevate contaminants including heavy metals, pesticides, mold, fungus and residual solvents," she added.
"Regulation of the production process is uneven across the U.S. if it exists at all, with the problem compounded by the proliferation of products and unscrupulous actors," Aussem said. "In some cases, 'testing' results and product labeling publicized to consumers have been manipulated or faked, resulting in fines and suspensions of those for-profit labs across the country that have been caught."
Other risks of concern include medication interactions; unintentional exposure to children and pets, leading to emergency room visits; use during pregnancy, which can result in developmental problems; use during adolescence, which can alter brain development; driving under the influence; and mental health impacts including depression, psychosis and anxiety, Aussem said.
"Consumers need to do their homework to ensure their cannabis use is not going to cause problems they didn't bargain for," she said. "And states need to step up their testing programs to assure adult cannabis consumers that they are getting exactly what is on the product label."
The findings were published online Wednesday in the journal Environmental Health Perspectives.
For more about the risks of marijuana, visit the Substance Abuse and Mental Health Services Administration.
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