Scientists have discovered more than 140 medications that alter the gut microbiome, forcing bacteria to compete for nutrients, a phenomenon known to cause an intestinal imbalance and prompt cancer-promoting inflammation. 

Stanford University researchers focused on common medications 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.

The impactful drugs included 51 antibiotics, certain chemotherapy medicines, antifungal medications and antipsychotics used to treat bipolar disorder and schizophrenia. 

The drugs created a new environment in the gut in which the most drug-resistant bacteria survived and weaker strains were killed off.

When drugs kill weaker populations of gut bacteria, however, all the sugars, amino acids and other molecules they were sustained on are left in the gut for the more dangerous strains to thrive on.

This allows harmful, inflammatory species to explode in growth, which can permanently alter the gut balance, creating a state that promotes cancer. 

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.

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