BOSTON: Marijuana smoke harms cells and DNA more than tobacco smoke does, while tobacco causes more intensive damage to chromosome structure, new research reports.
The study highlights the risks of marijuana, which are not as well known as those from smoking tobacco, said the authors, led by Rebecca Maertens a scientist with Canadian government research body Health Canada in Ottawa, Ontario. Their work is published in the August issue of the journal Chemical Research in Toxicology.
“It is clear that this information does not support the misconception popular among youth that marijuana is safer than cigarettes,” said Gary Holub a spokesperson for Health Canada.
Like tobacco, marijuana has been associated with respiratory problems such as chronic bronchitis. But neither marijuana plant extracts nor THC, the main psychoactive component of marijuana, have been definitively linked to lung cancer.
Establishing the exact risks of smoking marijuana has been difficult, the experts said, because most study subjects have also smoked tobacco.
The new study exposed bacterial and animal cells in the laboratory to smoke condensates, which are mixtures produced by dissolving filtered smoke particles. The mixtures were prepared in two different ways, one representing damage from smoking directly, the other from passive smoking.
The researchers found that marijuana smoke caused different types of genetic damage than tobacco smoke. Marijuana condensates were more likely to kill the cells or cause DNA damage. In contrast, tobacco condensates were more likely to change the structure of chromosomes within the cells.
Maertens’ team is continuing their cellular studies to determine the underlying reasons for these different responses. “Such work will help us better understand the potential health hazards of marijuana smoke exposure,” Holub said.
Wayne Hall, a public health professor and cannabis expert at the University of Queensland, in Australia, said the study confirms earlier evidence that marijuana smoke can produce mutations in genetic material.
However, the researchers did not show if those mutations are cancer causing, he said. “They do not enable us to estimate the magnitude of the risk.”
Jonathon Arnold, a pharmacologist at the University of Sydney who studies cannabis, added that the study will have a limited impact on the debate over marijuana use because it used cells, not human subjects.
However, he said the findings show that cannabis might be more damaging to the lungs than tobacco, but less likely to cause respiratory cancers. This could be because marijuana smoke is more likely to kill cells, he said. “As the cells are dead, they cannot progress to becoming cancerous through chromosomal damage.”
Arnold is the co-author of another marijuana study slated for publication in The British Journal of Pharmacology. It addresses the question of why ex-marijuana users sometimes test positive for the drug long after they stop using it.
The study showed that stress or food deprivation – conditions that promote the breakdown of fat in the body – cause stored THC to re-emerge into the bloodstream. The researchers called this phenomenon “reintoxication.”
In their study, Arnold’s team treated rats with THC daily for 10 days. Two days later, one third of the rats were injected with a stress hormone (ACTH), while one third were food deprived for 24 hours. The other rats served as controls.
The ACTH-treated rats doubled their THC blood levels, which put them in a “range where a large proportion of humans show cognitive and motor impairment,” Arnold said. The food deprived rats showed a doubled level of THC-acid, a metabolite of THC.
Positive drug tests
If this phenomenon carries over into humans, stress and extreme weight loss could be the reason behind ex-marijuana users’ positive drug tests. “This reintoxication could theoretically lead to a cannabis flashback,” Arnold said.
Next, the researchers will conduct human studies to determine whether reintoxication can cause a psychoactive effect or functional impairment.
Those future studies will be important to prove this either way, said Wayne Hall, who was not involved in the research. “It remains to be seen whether these effects can be replicated in humans.”
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