Dirty habit millions admit to daily linked to 20x higher colon cancer death rate, says shock study

People who smoke weed are up to 20 times more likely to die from colon cancer, a shock study suggests.

The study appears to blow the idea that cannabis can treat cancer – a myth that has prevailed in pro-weed circles for decades.

Researchers in California looked through health records from more than 1,000 people – all of whom had colon cancer.

They then compared cannabis users to non-users.

They found colon cancer patients with a history of using cannabis every day  or nearly every day had a 56 percent chance of dying within five years. 

This was an 11-fold difference compared to people who never used marijuana. 

And people formally diagnosed with cannabis use disorder – cannabis addiction – within months of being struck by colon cancer were 24 times more likely to die in five years compared to their peers.

The experts, from the University of California San Diego, believe THC, the active ingredient in cannabis that causes hallucinogenic effects, may cause inflammation in the colon, which causes cancer cells to grow.

THC may also block the production of disease-fighting T cells, which normally destroy cancer cells.

Additionally, cannabis use disorder may lead to depression and anxiety, making patients less likely to commit to cancer treatments. 

However, just three percent of participants had cannabis use disorder, and it’s unclear what stage their cancers were. 

The researchers said more studies are needed to understand how exactly cannabis addiction may increase the risk of colon cancer death. 

About 18million Americans use marijuana daily or nearly everyday, and about one in three are addicted to the substance. 

CUD is defined as using cannabis every day or nearly every day to the point where it negatively impacts a user’s life, such as making it difficult to hold down a job. 

Dr Raphael Cuomo, associate professor in the Department of Anesthesiology at UC San Diego School of Medicine, said: ‘This study adds to a growing body of evidence suggesting that heavy cannabis use may have underrecognized impacts on the immune system, mental health and treatment behaviors — all of which could influence cancer outcomes.’ 

Though the findings seem surprising, they come from the same institution that published a groundbreaking study last week tying the colon cancer epidemic in young Americans to childhood exposure to the common bacteria E. coli.

This would put nearly 100,000 Americans at risk. 

According to the latest data, early-onset colon cancer diagnoses in the US are expected to rise by 90 percent in people 20 to 34 years old between 2010 and 2030.  

In teens, rates have surged 500 percent since the early 2000s. 

Cannabis use is also on the rise, largely due to recent decriminalization across the US. 

From 1992 to 2022, for example, daily and near-daily use has seen a 15-fold rise. 

The new study, published Monday in the Annals of Epidemiology, look at medical records from 1,088 colon cancer patients in the University of California Health system between 2012 and 2024.

Of those, 34 were also diagnosed with cannabis use disorder. 

The average age at colon cancer diagnosis was 59. On average, patients with CUD were diagnosed four months before learning they also had colon cancer. 

After accounting for other health factors like age, gender and disease severity, the researchers found the risk of dying within five years of diagnosis for patients with an active cannabis addiction was 56 percent compared to five percent in non users. 

Additionally, patients diagnosed with CUD before colon cancer had a 24-fold increased risk of death within five years of diagnosis. 

The researchers wrote: ‘The results of this study indicate that a history of cannabis use disorder prior to colon cancer diagnosis is independently associated with an increased risk of mortality, even after adjusting for demographic and clinical confounders.’

The experts are unsure exactly what caused the surge in mortality rate, but based on past research, they suggested THC could lead to harmful inflammation in the colon. 

This inflammation suppresses T cells, a type of white blood cell meant to kill cancer cells. 

Inflammation also damages colon tissue over time, causing cells to rapidly form to help repair the destruction. The faster cells form, the more likely they are to divide and mutate into cancer cells. 

Additionally, cannabis may lead to mental health consequences. 

Dr Cuomo said: ‘High cannabis use is often associated with depression, anxiety and other challenges that may compromise a patient’s ability to engage fully with cancer treatment.’

The study directly contradicts some earlier research which has suggested some compounds in cannabis may inhibit cancer cell growth. 

A 2019 study from Penn State researchers of 370 synthetic cannabis compounds, for example, found 10 of them slowed the growth of seven forms of colon cancer. 

However, those researchers cautioned the mechanism behind this is unclear.

Dr Cuomo said further research is needed to understand the mechanisms of cannabis addiction and colorectal cancer. 

He also emphasized the findings don’t mean cannabis users have to quit entirely.

He sadi: ‘This isn’t about vilifying cannabis. It’s about understanding the full range of its impacts, especially for people facing serious illnesses. 

‘We hope these findings encourage more research — and more nuanced conversations — about how cannabis interacts with cancer biology and care.’