08/21/2025
The balance of gut bacteria and yeast has been shown to have far reaching effects on almost every other system in the body.
A new and rather alarming study has found that many drug medications targeting various systems in the human body might also change our microbiome so that pathogens can colonise the gut more easily and cause infections. The study, directed by Professor Lisa Maier of the Interfaculty Institute of Microbiology and Infection Medicine Tübingen (IMIT) and the Cluster of Excellence ‘Controlling Microbes to Fight Infections’ (CMFI) at the University of Tübingen, has been published in the elite journal Nature.
The researchers studied 53 common non-antibiotics, including allergy remedies, antidepressants and hormone drugs. Their effects were tested in the laboratory in synthetic and real human gut microbial communities. About one-third of these medications promoted the growth of Salmonella, bacteria that can cause severe diarrhoea. Lisa Maier, senior author of the study, says, “The scale of it was utterly unexpected. Many of these non-antibiotics inhibit useful gut bacteria, while pathogenic microbes such as Salmonella are impervious. This gives rise to an imbalance in the microbiome, which gives an advantage to the pathogens.”
The researchers observed a similar effect in mice, where certain medications led to greater growth of Salmonella. The consequence was severe disease progression of salmonellosis, marked by rapid onset and severe inflammation. This involved many layers of molecular and ecological interactions, such as reduced total biomass of the gut microbiota, harmed biodiversity or the specific elimination of microbes that normally compete for nutrients with the pathogens.
“Our results show that when taking medications we need to observe not only the desired therapeutic effect but also the influence on the microbiome,” says lead author Anne Grießhammer.
The researchers recommend that the effect of new medications on the microbiome should be systematically included in research during development – especially for drug classes such as antihistamines, antipsychotics or selective oestrogen-receptor modulators. These findings call for pharmaceutical research to be rethought: in the future, medications should be assessed not only pharmacologically, but also microbiologically. “If you disrupt the microbiome, you open the door to pathogens – it is an integral component of our health and must be considered as such in medicine,” stresses Maier.
However, it is important to emphasise that this research is preliminary and needs to be confirmed, and its impact in humans has still not been clearly established. These findings contrast with the growing insight from herbal research indicating that many phytochemicals in medicinal plants have the opposite effect, acting as prebiotics and thereby enhancing the growth of beneficial bacteria.
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