Professor Thomas M. Clark of the University of Indiana, while conducting the meta-analysis, found that cannabis use correlated with a decrease in various cancers, including head, neck and lung cancer and cancers associated with obesity. However, Clark also found that cannabis use was associated with a slight increase in testicular cancer.
Despite the interesting results, Clark says that these are not necessarily conclusive. This is due to the fact that the data sets were very heterogeneous. There were also not enough data sets for many types of cancer.
Risk factors for cancer types
Clark also noted that cannabis users tended to show a low rate of obesity. Obesity is a known risk factor for many cancers. He also noted that most cannabis users have a low rate of inflammation. This is also a risk factor for cancer. This finding is supported by previous research that has already shown links between cannabis use and a reduced risk of inflammation.
The results also showed that cannabis users tended to have improved insulin resistance and thus a lower risk of diabetes than non-users. This association could also contribute to a reduced risk of cancer. This is because poor insulin resistance and diabetes are associated with a higher risk of cancer, as well as faster cancer growth.
As a conclusion, Professor Clark summarised:
“The current analysis does not support the average recreational use of cannabis as an effective stand-alone cure for cancer. However, the results suggest that cannabis therapy added to established cancer treatment regimens not only significantly improves the quality of life of cancer patients, but could also improve the effectiveness of treatment without stimulating tumour growth”.
Clark added that cannabis use could potentially reduce the cancer-related death rate in the USA (around 600,000 people die of cancer every year). However, the available data would give little confidence in this conclusion. This is because there seem to be different responses among cancers. There would also be little or no data available for many cancers.
In addition, Clark notes that although a relationship between cannabis use and cancer can be proven, a causality cannot. Therefore, caution should be exercised in interpreting the data.