May 19, 2016 8:35 AM

WHO Report: Can Cannabis Cause Cancer?

A report recently released by the World Health Organization (WHO) contains a comprehensive review of all the significant research on the health consequences of the regular use of recreational cannabis. The experts assess the risks of cancer in cannabis smokers based on the last 20 years of research.

In the 20 since the publication of the previous WHO report on recreational cannabis, the situation with recreational marijuana use changed dramatically. The total number of U.S. states to legalize marijuana approached 24. The majority of those states allowed marijuana for medical use, however, recreational pot is now fully legal in Colorado, Washington, Alaska, Oregon, and the District of Columbia.

The WHO summarized the available knowledge on the plant and published a report on the health consequences of non-medical cannabis use. It is titled “The health and social effects of non-medical cannabis use” and contains the overview of the key studies on the subject.

The goal of the WHO was to publish the latest information on the effects of recreational cannabis use on physical and mental health. In this report, you can find everything we currently know about the relationship between long-term marijuana use and health problems.

Marijuana Use and Risk of Lung Cancer

A lot of people a concerned about the safety of cannabis, especially as the idea of marijuana legalization is gaining support across the nation. We all know that smoking tobacco can cause cancer. Could the same be true for cannabis?

In several studies, microbial assays and different tests in mice and rats showed that THC, as well as other cannabinoids, are not a carcinogenic. However, this cannot be said about marijuana smoke.

It is common knowledge that tobacco use sometimes leads to lung cancer in chronic heavy users. Careful scientific analyzes have identified nearly 50 carcinogenic chemicals—toxins, carcinogens, and irritants—in cannabis smoke similar to those present in tobacco smoke. This suggests that cannabis smoking may cause certain types of cancer, especially in teenagers: upper aerodigestive tract cancers, cancers of the pancreas, bladder, kidneys, stomach, liver, testicular cancer, and so on.

However, the cohort of studies provides little evidence for an increased risk of lung cancer among heavy cannabis users. Furthermore, certain compounds in the marijuana plant have been shown to possess anti-cancer properties.

Although subject to ongoing debate, the available study in the area suggests that cannabis smokers are at elevated risk for lung cancer and related illness, but the level of this risk lower than in tobacco smokers.

While a few low-quality studies associate marijuana use among youngsters with increased incidents of lung cancer. The studies in question, however, failed to use controls and did not account for confounding factors like tobacco use; no large case-control analyzes have been able to replicate these results. All available scientific data are based on poor lab information and strong qualitative similarity between the carcinogens found in pot and tobacco smoke.

In 2013, a group of Swedish scientists found that those smoking cannabis 50 or more times by the age of 18 were two times more likely to get lung cancer than non-smokers. This study was able to control only for baseline tobacco use but failed to include other confounding factors. Another study in North Africa has found a definite connection between cannabis and cancers. But all existing results cannot be considered as irrefutable evidence for the hypothesis due to the fact that in all the studies cannabis smoking has been confounded by cigarette smoking and other factors.

Although marijuana smoke contains a number of “bad” chemicals, findings from a small number of epidemiological studies do not suggest an increased risk for the development any type of cancer from light or moderate use; possible risks of heavy, long-term smoking marijuana raise concerns.

Anyway, the scientists claim that long-term cannabis smoking may produce symptoms of bronchitis, microscopical injury to bronchial lining cells, and different respiratory diseases.

All in all, cannabinoids themselves currently seem safe; it is the smoke that may be dangerous. Based on this, vaping or consuming cannabis edibles may be a safer option than smoking.

Upper Aerodigestive Tract Cancers

Cancers of the upper aerodigestive tract include cancer of the tongue, lip, throat, glands, gums, nose, and other organs and tissues. According to the Information and Statistics Division of Scotland, many of these cancers are caused by alcohol and tobacco use.

The hypothesis of a potential link between smoking marijuana and cancers includes a growing number of large-scale studies which, however, were unable to provide consistent evidence of the risks.

Several lines of evidence, including the presence of carcinogens and cocarcinogens in cannabis smoke, suggest that marijuana may predispose to cancers, particularly digestive tract cancers.

However, when the scientists adjusted the data to account for smoking tobacco and other common risk factors, they found that the link with marijuana was blurring. They concluded that if cannabis impacted cancers, the contribution is relatively small and cannot be considered significant. Some studies even showed a decreased risk of the upper aerodigestive tract cancers in cannabis smokers.

Testicular Cancers

All existing studies provide moderate and consistent relationships between cannabis smoking and testicular cancer. Since tobacco smoking is not linked to testicular cancer, there was no potential confounding by cigarette smoking. Three case-control studies in the United States showed that a history of cannabis use was associated with double the risk of nonseminoma testicular cancer. A meta-analysis found an odds ratio of 1.5 for chronic users and the same ratio for the patients consuming marijuana for ten or more years compared to those who have never used the substance.

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