Researchers from two medical centers in the Netherlands found that 18 categories of commonly used drugs had significant effects on the gut microbiome. The research was presented at United European Gastroenterology (UEG) Week 2019 in Barcelona, Spain. 

The gut microbiome consists of all the bacteria that live in our intestines. When in balance, the gut microbiome can provide a range of benefits for our health. However, when that balance is disturbed, we have a higher risk of developing serious infections, cancers and different chronic diseases. 

The study, conducted by the University Medical Center Groningen and the Maastricht University Medical Center, examined how 41 commonly used drug categories affected patients with inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). The population-based cohort included 1883 fecal samples using healthy patients as controls. 

There were several notable findings in the study:

Proton pump inhibitors (PPIs) - used to treat dyspepsia, peptic ulcer, H. Pylori eradication, Gastro reflux and Barrett’s esophagus. PPI users showed higher amounts of bacteria in the gastrointestinal tract, in addition to an increase in the production of fatty acid. 

Metformin - used to treat Type 2 diabetes. Associated with higher populations of E. coli. While many strains of E. coli are harmless in the gut, some can cause food poisoning when eaten or serious infections when spread to other body parts.

Oral steroids - used to reduce inflammation, were associated with a bacteria species linked to an increase in BMI and obesity.   

Selective serotonin reuptake inhibitors (SSRIs) - used to treat depression, demonstrated an increase in a potentially harmful bacteria species. 

Eight different drug categories were associated with increased antibiotic resistance. Antibiotics, which have the side effect of disrupting the gut microbiome, are necessary for treating serious infections. But with the advent of overprescription of antibiotics, more patients are unnecessarily depleting their gut microbiome or generating antibiotic-resistant bacteria strains. Stronger antibiotics needed for resistant strains cause greater damage to the gut microbiome. 

Though these drugs are important for addressing many diseases and conditions, research demonstrates a need for greater awareness of how medication use can affect the gut microbiome. 


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