By / November 16, 2020

The use of cannabis could reduce the risk of cancer

Cannabis smoke contains ingredients that have anticancer properties – the best known are THC and CBD. But it also contains substances that increase the risk of cancer, including nitrosamines and polycyclic aromatic hydrocarbons.

It is not yet clear how this combination affects cancer risk. According to a detailed meta-analysis of all studies conducted on the subject to date, a researcher from the Department of Biological Sciences at Indiana University in South Bend, USA, concludes that smoking cannabis significantly reduces the risk of cancer in the USA (Clark 2020).

However, in order to make optimal use of the cancer-inhibiting properties of cannabis, cannabis should not be smoked. It should be vaporized, or taken orally. A total of 34 studies were considered.

Quality control in the meta-analysis

The results show a trend towards a reduced risk of developing cancer from smoking cannabis by about 10 percent. If studies with a high probability of bias were excluded, the reduced risk was statistically significant at 14 percent.

The author assumed a high probability of studies distorting the results if the studies were from North Africa, or if tobacco consumption was not taken into account, or where there were fewer than 20 cases sampled.

Not all cancers affected equally by cannabis use

For testicular cancer, there was a non-significant increase in cases of 12 percent. Yet, even after the additional risk for testicular cancer, the remaining data still showed a significant overall decrease in risk by 13 percent.

Cancers of the head and neck showed a highly significant decrease in cancer risk of 17 percent while, for other cancers like lung cancer, there were no significant differences between cannabis smokers and non-smokers.

In summary, only testicular cancer showed a tendency towards a slightly increased risk, but this was not statistically significant. For all other cancers, there was a tendency to a slightly decreased risk, but this was only statistically significant for head and neck cancer. The author wrote that the “current analysis suggests that cannabis use in the United States could reduce the risk of cancer by 10 % (…). “

The results of the study

Given the importance of cancer in the total number of deaths in the United States – about 600,000 people die of cancer every year in the United States – the authors point out that “cannabis use could significantly reduce the cancer-related death rate in the United States. However, the available data gives little confidence in this conclusion. There appear to be different responses among cancers and, for many cancers, there is little or no data available.”

In addition to the great variation in results between different studies and other factors, the author notes that although a relationship between cannabis and cancer can be demonstrated, “no causality can be established. Therefore, caution is needed when interpreting these data. Nevertheless, the data suggest that cannabis use may reduce cancer risk in the United States.”

Reduced risk of cancer due to cannabis use not surprising

A reduced risk of cancer in cannabis users should not come as a surprise, as cannabis and cannabinoids reduce obesity, inhibit chronic inflammation, lower fasting insulin levels and insulin sensitivity, and have direct anti-tumor effects. These are all factors that can have a beneficial effect on the development of cancer.

In addition, the respiratory tract and bladder would be exposed to the highest concentrations of carcinogens of cannabis smoke, but the risk of cancer of the mouth, throat, larynx, and bladder is significantly reduced in cannabis users. This shows that the carcinogenic effects of cannabis constituents outweigh the carcinogenic effects of cannabis smoke itself in the respiratory tract and bladder, where exposure to carcinogens is high.

Cannabis contribution to reduced cancer risk could be greater than initial estimate

It is possible that the actual reduction in cancer risk from cannabis use is even greater than the estimated 10 percent reduction in risk that emerges from the current analysis.

This is because there is little data on the effects of cannabis use on the relative risk of cancers other than those that are exposed to the carcinogens of smoke, such as those associated with obesity, such as cancer of the liver, breast, colon, stomach, and prostate. There are also studies that show that regular cannabis users are less obese and have a lower body mass index.

More data is needed to explore effects of cannabis on other cancers

Some cancers are relatively common, while others are rare, and some types have a much higher mortality rate than others. In the current data set, only testicular cancers show a trend towards an increased risk among cannabis users, and testicular cancer is a relatively rare cancer with a high survival rate.

For many other cancers, there is little to no data on the association with cannabis use. The actual impact of cannabis use on cancer cases and deaths can therefore not be estimated with certainty using the data currently available. The author of the review points out that “given the large number of cancer diagnoses and the large number of people who use cannabis, however, even a moderate effect on cancer risk will have a significant public health impact.“

(Featured image by TerreDiCannabis via Pixabay)


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First published in Hanf Journal, a third-party contributor translated and adapted the article from the original. In case of discrepancy, the original will prevail.

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