Cannabis is now linked to rising cancer rates in young people, and the evidence is growing harder to ignore. A major new study suggests that cannabis and young adult cancer risk are more closely connected than previously thought, with cannabis use potentially driving an alarming increase in breast and testicular cancer among adolescents and young adults aged 15 to 39. Cancer incidence in this group has risen by 30% over the past four decades.

Obesity, sedentary lifestyles, and hereditary factors have long been cited as possible causes. But the role of cannabis has only recently come under the spotlight.

A Pattern Emerging Across Borders

Dr Rebecca H. Johnson led the study. She is Medical Director of the Adolescent and Young Adult Oncology Programme at Mary Bridge Children’s Hospital in Tacoma, Washington. Her team compared breast and testicular cancer rates across US states that had legalised cannabis and those that had not. They also examined trends in Canada, where cannabis became legal for medicinal use in 2001 and for recreational use in 2018.

The findings were striking. In cannabis-legalising US states, breast cancer rates in women aged 20 to 34 rose by 26%. In non-legalising states, the rise was 17%. Testicular cancer in males aged 15 to 39 climbed by 24% in legalising states, against 14% elsewhere.

Canada painted an even more alarming picture. Breast cancer rates among young Canadians rose by 35% over the same period. Testicular cancer surged by 83%. Dr Johnson links Canada’s sharper increases to its earlier and broader legalisation of the drug.

Why Cannabis May Pose a Cancer Risk

Cannabis is a known endocrine disrupter. It acts on reproductive organs through cannabinoid receptor 1 (CB-1), present in both breast and testicular tissue. When adolescent breast cells encounter cannabis, structural changes occur. These changes may raise cancer vulnerability during a critical window of development.

There is also a hormonal element. Cannabis suppresses luteinizing hormone, which activates several gonadotropin receptors. One of those, gonadotropin-releasing hormone 2, protects against breast cancer. Suppressing it could plausibly raise risk.

Cannabis potency has also increased sharply. THC concentration rose from around 4% in the 1990s to over 14% in 2019. Today’s young users are exposed to a far stronger substance than any previous generation.

Australian researchers have separately concluded that cannabis meets the epidemiological criteria for causality in 25 of 41 cancer types. They also found it to be a more potent carcinogen than alcohol or tobacco. That finding alone places cannabis and young adult cancer risk at the centre of a serious public health debate.

The Speed of the Effect Is Alarming

Dr Johnson’s study raises another troubling question: how fast does the risk develop? Population-level data suggests that cannabis accelerates these cancers within five to ten years of exposure. Some evidence points to even less time than that.

“It appears that the carcinogenic effect of cannabis on AYAs is rapid, leading to cancer within just a few years of exposure,” said Dr Johnson.

Cannabis use disorder peaks among 18 to 25 year olds. This is precisely the group most affected. Young people who start using cannabis in their teens could face elevated cancer risks long before they reach middle age.

Triple-Negative Breast Cancer: A Particularly Worrying Finding

The study found that cannabis-linked cancer in young adults appears strongly associated with triple-negative breast cancer. This subtype carries a worse prognosis than hormone-receptor-positive forms. It is also harder to treat.

Researchers do not yet fully understand why this link exists. Further investigation is ongoing.

Cannabis During Cancer Treatment

Beyond the question of cancer risk, the study raises concerns about cannabis use during treatment. A prospective observational study found that cancer patients using cannabis during immune checkpoint inhibitor therapy fared significantly worse. Their median time to cancer progression was 3.4 months. Non-users reached 13.1 months. Median overall survival was 6.4 months for cannabis users, against 28.5 months for those who did not use it.

Many young patients use cannabis to manage side effects such as nausea and pain. If larger trials confirm these figures, the consequences for treatment outcomes could be serious.

A Generation at Risk

Today, 47 US states permit medical cannabis use. Twenty-four allow recreational use. The drug is accessible nearly everywhere. Yet awareness of cannabis and young adult cancer risk remains low among the people most affected.

Dr Johnson is calling for more research into the biological mechanisms involved. She also wants greater public awareness of the potential harms, especially for young people still in critical stages of development.

Other factors do play a role. Children and adolescents in the United States now get 62% of their daily calories from ultra-processed foods, a pattern researchers have linked to rising cancer rates. The causes are clearly multiple. But cannabis now demands a place in that conversation.

Source: ascopost