A STUDY published in June that I have just come across provides unsurprising but nonetheless devastating and irrefutable evidence linking increased cannabis use with rising rates of breast and testicular cancers in young Americans.
The study covers the period between 2000 and 2019. The aim was clear: to test the hypothesis that the increasing incidence of testis and breast cancer in adolescent and young adult (AYA) Americans correlates with their increasing cannabis use. Its conclusions are stark: that North America has evidence which implicates cannabis as a potential etiologic factor contributing to the increasing incidence of breast carcinoma in young females and testis cancer in older adolescent and young adult males, and in most races and ethnicities. Temporal correlations suggest that a carcinogenic effect of cannabis is rapid, leading to cancer within a few years after cannabis exposure. You can read this extremely detailed and careful study here.
Its overall study design involved comparing breast and testis cancer incidence trends in jurisdictions that had and had not legalised cannabis use. In the US, both breast carcinoma in 20- to 34-year-old females and testis cancer in 15- to 39-year-old males had annual incidence rate increases that were highly correlated (Pearson’s r = 0.95) with the increase in the number of cannabis-legalising jurisdictions during the period 2000–2019. Both were significantly greater during the period 2000–2019 in the cannabis-legalising than non-legalising states. (My italics)
During the period 2000–2019, registries in cannabis-legalising versus non-legalising states documented a 26 per cent versus 17 per cent increase in breast carcinoma and 24 per cent versus 14 per cent increase in testis cancer.
In the same age groups, the study (predictably) found Canada had an even greater increase in both breast and testis cancer incidence than the US. A UNICEF study on the well-being of children had already confirmed that Canadian adolescents (aged 11 to 15) have the highest rate of cannabis use among the 29 advanced economies of the world. Of particular concern that legalising advocates would do well to note is the considerable percentage of the Canadian youth who are daily or weekly users – approximately 22 per cent of boys and 10 per cent of girls. And that amongst the older 16-19s the upward trend in use which increased to 43 per cent in 2023 compared with 36 per cent in 2018 follows the country’s nationwide legalisation of cannabis for over-18s in 2018.
This link between cannabis and these forms of cancer should come as no surprise. A report from the American Cancer Society (ACS) in February this year identified non-seminoma testis cancer as the cancer type most closely linked to cannabis use.
More shocking is that this relationship has been known about for years. In 2009, scientists at the Fred Hutchinson Cancer Research Centre in Seattle investigated the possibility of a link ‘after learning that the testes were one of the few organs in the body to contain receptors for the main psychoactive substance in the drug, tetrahydrocannabinol (THC)‘. The same scientists noted that there had also been a rise in testicular cancer cases that had ‘mirrored the rise in marijuana use since the 1950s’.
The 2025 study is of course of a different type and order of magnitude. It was certainly needed. Its findings warrant the utmost attention of our national and local public health authorities which were so zealous to promote child covid vaccination but have remained over the years so strangely silent about cannabis.
This valuable study should also serve as a warning to cannabis legalisers including Sir Sadiq Khan that their endorsement of the drug and indifference to the impact of legalisation on teen health is not just irresponsible but near-criminal.
Postscript: There are other disturbing elements regarding the underlying mechanisms noted in the study’s findings. These, its authors state, ‘may involve genotoxic effects, oxidative stress, and mitochondrial dysfunction caused by cannabis, leading to genomic instability’. For further elucidation of this a 2024 study published in Addiction Biology provides some key insights into cannabis-cancer pathobiology and genotoxicity. You can read this report here.
