People who only smoked marijuana had higher blood and urine levels of several smoke-related toxins such as naphthalene, acrylamide and acrylonitrile than nonsmokers, according to the study published Monday in the journal EClinicalMedicine.
Naphthalene is associated with anemia, liver and neurological damage, while acrylamide and acrylonitrile have been associated with cancer and other health issues.
"Marijuana use is on the rise in the United States with a growing number of states legalizing it for medical and nonmedical purposes - including five additional states in the 2020 election," said senior author Dr. Dana Gabuzda, a principal investigator in cancer immunology and virology at the Dana-Farber Cancer Institute in Boston, in a statement.
"The increase has renewed concerns about the potential health effects of marijuana smoke, which is known to contain some of the same toxic combustion products found in tobacco smoke," Gabuzda said.
The new research presented data from three studies of 245 HIV-positive and HIV-negative participants. Researchers said they chose to study people with HIV infection because of the high prevalence of tobacco and marijuana smoking typically found in this population.
Medical records were compared to blood and urine samples of various chemicals produced by the breakdown of nicotine or the combustion of tobacco or marijuana.
Tobacco and tobacco-marijuana smokers had higher levels of naphthalene, acrylamide and acrylonitrile than marijuana-only smokers. Tobacco smokers also had increased levels of a chemical called acrolein in their blood and urine. Acrolein is a known contributor to cardiovascular disease in tobacco smokers.
Marijuana smokers, however, did not have higher levels of acrolein in their bodies.
"This is the first study to compare exposure to acrolein and other harmful smoke-related chemicals over time in exclusive marijuana smokers and tobacco smokers, and to see if those exposures are related to cardiovascular disease," Gabuzda said.
Acrolein is a chemical with a burnt, sweet, pungent odor created by the burning of fuels such as gasoline or oil and organic matter such as tobacco. The chemical is not added to cigarettes; acrolein is produced by the burning of sugars present in tobacco when smoked.
Short-term exposure to acrolein can cause upper respiratory tract irritation and congestion. At extreme levels, it can be toxic to humans following inhalation, oral or dermal exposures, according to the US Environmental Protection Agency.
While weed smokers had higher amounts of naphthalene, acrylamide and acrylonitrile in blood and urine than nonsmokers, even higher levels were found in people who smoked tobacco or a combination of marijuana and tobacco.
Acrylamide is a chemical used to make paper, plastics and dyes, but is also produced when vegetables such as potatoes are heated to high temperatures. It is also a component of tobacco smoke.
"People are exposed to substantially more acrylamide from tobacco smoke than from food. People who smoke have three to five times higher levels of acrylamide exposure markers in their blood than do non-smokers," stated the National Cancer Institute. According to the American Cancer Society, the International Agency for Research on Cancer classifies acrylamide as a "probable human carcinogen," while the US National Toxicology Program says it's "reasonably anticipated to be a human carcinogen," based on animal studies.
Acrylonitrile is typically used in the manufacturer of plastics and fibers. "Cigarette smoking can be a significant source of acrylonitrile indoor air pollution," according to the World Health Organization.
Symptoms of acrylonitrile poisoning include "limb weakness, labored and irregular breathing, dizziness and impaired judgment, cyanosis, nausea, collapse, and convulsions," the US Environmental Protection Agency said. And a "statistically significant increase in the incidence of lung cancer has been reported in several studies of chronically exposed workers."
The EPA classifies acrylonitrile as a "probable human carcinogen."
Naphthalene, which is used in mothballs, can cause "headache, nausea, vomiting, diarrhea, malaise, confusion, anemia, jaundice, convulsions, and coma," according to the EPA.
The highest concentrations of naphthalene in indoor air occurs in the homes of cigarette smokers, the US Centers for Disease Control and Prevention said.
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