Some everyday medicines — not just antibiotics — could influence gut bacteria in ways that affect how other treatments work, according to a new review by the United Kingdom’s Medicines and Healthcare products Regulatory Agency (MHRA) and University of Glasgow. The findings open up opportunities to better tailor treatments to individuals and improve how medicines are used together in real life. 

The review, published in Nature npj Antimicrobials and Resistance, brings together evidence that a wide range of drugs — including diabetes treatments and antipsychotics — can change the make-up of the trillions of bacteria in our gut that keep us healthy. These subtle changes could impact how medicines work in the body, particularly when treatments are taken together. 

Understanding how drugs interact with gut bacteria could help researchers and the MHRA build on the strong existing evidence around medicine safety, better understand why some people respond differently to the same medicine, and support the development of treatments that are increasingly  safer and more effective over time.  

Dr Chrysi Sergaki, senior author of the study and Head of Microbiome at the MHRA, said: “Antibiotics are well known to affect gut bacteria, but this review shows that some other common medicines can also influence the microbiome. Building this understanding helps us identify where better data could improve drug development and, ultimately, patient care — while also supporting the responsible use of antibiotics. 

“These findings could help researchers understand why some patients respond differently to the same treatment, and why certain side effects occur in some people but not others.”  

The gut microbiome — the community of trillions of bacteria that live in the digestive system — plays a key role in immunity and metabolism. While the effects of antibiotics on this balance are well established, the review highlights evidence that several non-antibiotic medicines may have similar, if more subtle, effects.  

Some examples from the review include metformin, a widely used diabetes medicine, which alters gut bacteria in ways that may contribute to both its benefits and some side effects such as bloating or diarrhoea. Antipsychotic medicines have been shown in studies to disrupt gut bacteria linked to weight gain and metabolic changes.

(Source: MHRA)

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Published on December 29, 2025