More than 140 Medications Disrupt Gut Health and Drive Colorectal Cancer Risk
Scientists have identified more than 140 medications that alter the gut microbiome, forcing bacteria to compete for nutrients—a shift known to cause an intestinal imbalance and prompt cancer-promoting inflammation. Stanford University researchers focused on common drugs that impact the vast array of microbes in the gut, with potentially far‑reaching consequences for metabolism, immune system response and overall health. They found that potentially deadly changes in the gut result from certain medications killing off populations of bacteria and changing the availability of nutrients.
In This Article:
- Drugs reshuffle the gut buffet, allowing drug‑resistant bacteria to thrive
- The experiment that mapped 707 drugs on a human‑like gut ecosystem
- A striking example: antifungal bifonazole disrupts bacterial food supply
- Damage often permanent; dysbiosis fuels chronic inflammation and cancer risk
- Dysbiosis and cancer‑promoting byproducts like colibactin
- Superbugs and a rising colorectal cancer tide among younger adults
- A new tool for predicting drug impacts and guiding microbiome‑preserving therapy
- Personal stories connect science to real people
Drugs reshuffle the gut buffet, allowing drug‑resistant bacteria to thrive
The drugs created a new environment in the gut in which the most drug‑resistant bacteria survived and weaker strains were killed off. Lead researcher Dr Handuo Shi said in a statement: ‘In other words, drugs don’t just kill bacteria; they also reshuffle the "buffet" in our gut, and that reshuffling shapes which bacteria win.’ Dr KC Huang, a microbiologist and immunologist at Stanford, and lead researcher, added: ‘Understanding how microbes are competing for food ends up telling a really large part of this collateral damage story. It enables us to predict who is going to live, who is going to die, and makes the ensuing chaos seem really intuitive. I think that’s what we’re most excited about.’ The surviving bacteria are able to reshape the body's microbiome, the collection of healthy bacteria that boosts the immune system and fights viruses, into a pro‑inflammatory state, raising the risk of colorectal cancer.
The experiment that mapped 707 drugs on a human‑like gut ecosystem
The research team took a human fecal sample, used it to colonize a mouse, and then used its gut contents to create a stable microbial community that they could grow in a lab dish. The bacterial community in their guts contained dozens of different species interacting as they would in a human gut. Then, they exposed the mice to 707 different drugs, one per experiment, all at the same concentration. After growing over a dozen communities of bacteria with the drugs, they tested how many of those communities of bacteria survived after being introduced to the medications, the nutrients and waste products left behind from dying strains and measured the overall growth of the community as a whole to see how much each drug inhibited it.
A striking example: antifungal bifonazole disrupts bacterial food supply
A key example researchers found pertained to two beneficial bacterial species, which survived in a test tube when exposed to the antifungal drug bifonazole. The bacteria rely on an iron‑containing molecule called heme for food, which scientists added. In the gut, these same bacteria do not get their heme directly and must rely on other bacteria to produce and supply it. The antifungal drug, however, killed the bacteria that usually provide this crucial compound, cutting off the species' food supply. Suddenly starved and weakened, the beneficial bacterial species became vulnerable to a drug they could previously resist, allowing harmful strains of bacteria to take up the leftover nutrients and flourish.
Damage often permanent; dysbiosis fuels chronic inflammation and cancer risk
The damage caused by the 141 drugs that wiped out entire communities of bacteria was often permanent, with communities failing to return to their original states after the drugs were removed. The resulting imbalance creates a state of chronic inflammation in the gut, which can damage colon cell DNA and fuel processes that lead to colorectal cancer. An imbalanced microbiome also disrupts the mucosal barrier lining the intestines, allowing toxins and other harmful substances to leak into the intestinal tissue, which further fuels constant low‑grade inflammation and spurs the development and clumping of cancer cells into tumors.
Dysbiosis and cancer‑promoting byproducts like colibactin
An imbalance, also known as dysbiosis, can produce harmful waste and byproducts known to promote cancer, including colibactin produced by certain E. coli bacteria. Colibactin damages the DNA of colon cells, leading to mutations that influence the development of cancer.
Superbugs and a rising colorectal cancer tide among younger adults
Doctors across the US have been sounding the alarm for years about a rising number of bacterial strains that have become resistant to common antibiotics, requiring high doses of less commonly used drugs. These drug‑resistant infections have since been dubbed ‘superbugs.’ The American Cancer Society's most recent investigation revealed a dramatic surge in colorectal cancer among adults under 55, with diagnoses in 45‑ to 49‑year‑olds accelerating from a one percent annual increase before 2019 to a 12 percent yearly rise through 2022. A separate analysis posited that colon cancer is among the fastest‑growing cancers in young adults, particularly 20 to 29‑year‑olds, where cases are surging by 2.4 percent per year on average. The disease has already been projected to become the most common cancer in people under 50 by the year 2030.
A new tool for predicting drug impacts and guiding microbiome‑preserving therapy
The Stanford team’s work gives other scientists a tool to predict a drug's impact on gut bacteria, opening the door to strategies that protect or rapidly rebuild a healthy microbiome after treatment. Shi said: ‘Our study pushes a shift from thinking of drugs as acting on a single microbe to thinking of them as acting on an ecosystem.’ ‘If we can understand and model the ecosystem response, we could one day choose drugs and accompanying diets or probiotics not only based on how well they treat a disease, but also on how they preserve or promote a healthy microbiome.’ Their findings were published in the journal Cell.
Personal stories connect science to real people
Marisa Peters, a mother of three from California (pictured here), then 39, was diagnosed with stage three rectal cancer in the summer of 2021. Peters' cancer is considered early‑onset, referring to cases in people under 50, which are on the rise in the US Trey Mancini (pictured here) was diagnosed with 'aggressive' stage three colon cancer at 28. He told DailyMail.com if he had not had routine bloodwork done for baseball, he may not have been diagnosed 'until it was too late'.
