Could Marijuana Cause Cancer? Secondhand Smoke From Drug Causes More Viral Infections in Children Than Tobacco

That same group was also 37% more likely to develop a viral respiratory infection, and had a greater incidence of ear infections than the control groups.

There were 1,500 caregivers in the study, 11.1% of whom identified as marijuana smokers. Of that group, 95% said that they smoked daily or weekly, and most preferred to vape the drug.

“The potential for increased respiratory infections with marijuana exposure could have significant healthcare implications as more states move toward legalizing the recreational use of marijuana,” note the authors of the study. “While the dangers of primary marijuana use are becoming more evident, secondhand marijuana smoke exposure may also need to be addressed.”

The study also makes a point of stating that many marijuana users still choose not to share they fact that they use the drug, citing a 2018 study published in Pediatrics that found traces of a compound linked to secondhand marijuana smoke in the urine of 47% of children whose parents were enrolled in smoking cessation courses at a Colorado hospital.

This makes it more likely to blame health problems on just tobacco use rather than a combination of tobacco and marijuana, especially in studies done in the years before the drug was legal.

"The findings of this study are interesting and pleasantly raise further questions," said Dr. Kristen Miller, an attending physician at Children's Hospital of Philadelphia, who was not involved in the study. "Given the robust literature regarding secondhand smoke exposure and the current landscape surrounding marijuana, this is a timely study to evaluate the prevalence of marijuana use and the associated effects of marijuana exposure among children."

Does Marijuana Use Cause Cancer?

SurvivorNet’s extensive review of the medical literature finds no high-quality scientific research establishing a direct link between smoking, or vaping, marijuana and an increased risk of developing lung cancer. This is largely due to the fact that smoking pot was illegal for so long and therefore not easy to study in a long term way.

Its medicinal use was first legalized just 25 years ago, and it has been just nine years since the first states approved recreational use of the drug.

Further compounding the problem is the fact that a high percentage of marijuana smokers also use tobacco products.

In fact, a 2017 study by researchers at Columbia University's Mailman School of Public Health found that “marijuana use occurred nearly exclusively among current cigarette smokersdaily or non-daily smokerscompared with former smokers and those who have never smoked.”

Experts tell SurvivorNet that a large scale study is necessary to definitively examine the link between marijuana and lung cancer, as well as to help educate millions of people who are smoking marijuana recreationally.

"Given the expanding legalization of marijuana, and the anticipated wave of increased use, there is clearly a need to study the cancer risks of marijuana with the same rigor that has been devoted to tobacco smoke," Dr. Joseph Friedberg, head of the Division of Thoracic Surgery at the University of Maryland School of Medicine, previously told SurvivorNet. "Both types of smoke contain some of the same carcinogens, so the widely held belief that tobacco smoke causes cancer and marijuana smoke does not is inherently flawed."

He also noted: “Just as cigarettes come with health risk warnings, the risks of marijuana smoke need to be defined for users to allow them to make an informed decision about smoking pot.”

In 1965, Congress passed an act the required every pack of Marlboros, Camels, and Pall Malls sold in the United States to come with a warning that read: “Caution: Cigarette Smoking May Be Hazardous to Your Health.”

Thirty-one years after the passage of the Federal Cigarette Labeling and Advertising Act of 1965, California became the first state to legalize the medical use of marijuana.

In the years since, 36 states have followed suit and passed legislation that allows for the use of medicinal marijuana. And half of those states have gone one step further and also legalized recreational use of the drug.

There has not, however, been any law passed that requires a warning label which states the potential risks associated with smoking or consuming cannabis.

Dr. Donald Tashkin, a pulmonologist from UCLA, has studied marijuana for 30 years. He has published research, written review articles, and given talks to doctors on the topic. He says there is a lot of evidence to suggest marijuana may cause cancer. This includes:

• Known carcinogens in the smoke of marijuana
• Genes implicated in the development of lung cancer are over expressed in the lungs of pot smokers
• Tissue in the lungs of marijuana smokers compared to non-smokers have a higher proportion  precancerous changes

But Tashkin says when you look at human studies the evidence is not there. Tashkin says of the six well done human studies five showed no association between marijuana and lung cancer and the sixth actually shows a benefit. “The weight of evidence thus far available would argue against a significant association,” Tashkin says. And he says when he gives talks to doctors they “scratch their head when they look at the evidence because the expectation is that there should be a positive association between marijuana smoking and lung cancer.”

Learn more about SurvivorNet's rigorous medical review process.

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