A large study led by researchers at the University of Tartu Institute of Genomics has found that common medications can leave a lasting imprint on the community of microbes living in the human gut, with differences still detectable long after a person stops taking the drug. The work drew on stool samples and prescription records from more than 2,500 people and reported that the effect was not limited to antibiotics, which are already known to disrupt gut bacteria. Antidepressants, beta-blockers, acid-reducing drugs and anti-anxiety medications were each associated with distinctive microbial signatures that persisted well beyond the end of treatment.
The findings describe statistical associations between past prescriptions and later microbiome composition rather than proof that any single drug caused a specific change in a given person. Even so, the pattern was consistent enough that the authors argue a person’s prescription history may help explain differences in gut bacteria that researchers have often struggled to account for. The gut microbiome, the vast collection of bacteria and other organisms in the digestive tract, is thought to influence digestion, metabolism and immune function.
How the Estonian Biobank data were analyzed
The researchers examined participants in the Estonian Microbiome cohort, part of the Estonian Biobank, linking each person’s stool sample to detailed prescription records. That linkage let the team look backward in time and ask whether a drug taken months or years earlier still tracked with the makeup of the microbiome measured in the present. Most of the medications examined were associated with differences in gut bacteria, and for a substantial number of drugs those differences remained visible years after people had stopped taking them. The full peer-reviewed report describes the cohort and the statistical approach in detail.
Why past prescriptions, not just current ones, matter
Most microbiome research considers only the medications a person is taking at the time a sample is collected. The Tartu team found that approach can miss a major influence. Oliver Aasmets, the study’s lead author, said past drug use can be just as important as current use and is a surprisingly strong factor in explaining individual microbiome differences. That distinction has practical consequences, because studies searching for links between the microbiome and disease could mistake the lingering fingerprint of an old prescription for a signal related to illness.
Antidepressants and other everyday drugs leave marks
Beyond antibiotics, the study flagged several widely prescribed drug classes. Antidepressants, beta-blockers used for high blood pressure and heart conditions, proton pump inhibitors that reduce stomach acid, and benzodiazepines used for anxiety were all associated with distinctive microbial patterns. Because these medications are taken by large numbers of people, sometimes for years, their collective footprint on the population’s gut bacteria may be considerable. The associations were drawn from real-world health records rather than a controlled laboratory setting, which the authors present as a strength for understanding everyday exposure.
Anxiety medications rival broad-spectrum antibiotics
One of the more striking findings involved benzodiazepines, the class commonly prescribed for anxiety. Their association with the gut microbiome was comparable in magnitude to that of broad-spectrum antibiotics, which are designed to kill many kinds of bacteria and are expected to reshape the gut substantially. The study also found that drugs within the same class did not necessarily affect the microbiome in the same way. Diazepam and alprazolam, both prescribed for similar conditions, differed in how strongly they appeared to disturb gut microbes, suggesting that grouping medications only by class may obscure important differences.
Follow-up samples point toward the drugs themselves
To test whether the medications were driving the changes rather than merely coinciding with them, the researchers examined follow-up stool samples from a smaller group of participants, observing what happened when people started or stopped a drug. Those transitions were accompanied by predictable shifts in gut microbes, evidence that the medications themselves were responsible for at least part of the difference. The team confirmed persistent effects tied to proton pump inhibitors, selective serotonin reuptake inhibitors and certain antibiotics, including penicillin combinations and macrolides, though the authors noted the second analysis involved relatively few people.
What the results mean for medical research
The study adds to growing evidence that the gut microbiome reflects more than a person’s current diet, lifestyle and health. Elin Org, the corresponding author, described the work as a comprehensive systematic evaluation of long-term medication effects using real-world medical records and said she hopes it encourages researchers and clinicians to factor in medication history when interpreting microbiome data. Accounting for that history could help scientists more cleanly separate microbiome changes associated with disease from changes that trace back to drugs taken in the past. The journal article in mSystems frames the issue as a hidden confounder that microbiome studies have often overlooked.
Context and cautions for readers
The study does not suggest that people should stop taking prescribed medications, and its authors did not draw clinical recommendations about treatment. The associations describe population-level patterns, and the persistence of a microbial fingerprint does not by itself establish that a person’s health has been harmed. What the work does highlight is that the timeline over which drugs interact with the gut is longer than often assumed, stretching from months into years for some compounds. A plain-language summary of the findings notes that the results emerged from more than 2,500 participants and were published in a peer-reviewed microbiology journal, underscoring that medication history may deserve a larger role in how the microbiome is studied.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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