Everyday Prescriptions Leave Lasting Mark on Gut Bacteria, Large Estonian Study Finds

Antibiotics have long carried the reputation as the gut's worst chemical landlord. A study published this month in the American Society for Microbiology's journal mSystems suggests the list of culprits is considerably longer, and the damage lasts considerably longer than most clinicians have discussed with patients.

Researchers at the University of Tartu Institute of Genomics in Estonia linked stool metagenomic data from 2,509 people to their electronic health records, capturing up to five years of prescription history per participant. As ScienceDaily reported on August 24, the team found that medications can influence gut microbial communities long after a patient stops taking them.

The drug classes showing lasting effects weren't fringe prescriptions. According to findings reviewed in the mSystems commentary, nearly half of the 186 drugs tested were associated with microbiome changes that persisted for years after the last dose, with antibiotics, beta-blockers, benzodiazepine derivatives, proton-pump inhibitors, and antidepressants all on that list. For some medications, the effects were additive: the longer and more frequently a person had used a drug, the more pronounced the microbial disruption.

Among individual drug classes, benzodiazepines showed some of the strongest independent effects. The researchers also found, per The Scientist's coverage of the findings, that 42 percent of the drugs studied were still associated with microbiome changes even when last used more than a year before the stool sample was collected.

For patients who take multiple medications continuously, as millions of Americans do for conditions like hypertension, depression, or reflux, those effects can stack. A commentary on the paper published in mSystems noted that researchers studying links between disease and the microbiome should start treating past drug use as a confounding variable, not just current prescriptions.

The study population is an important caveat here. These are Estonian adults whose prescription patterns and dietary habits differ in meaningful ways from, say, a patient on Medicaid in rural Mississippi managing type 2 diabetes and depression simultaneously. The findings offer a signal, not a map that translates cleanly to every clinical context.

What the data do challenge is a common clinical assumption: that once a patient stops a medication, its GI effects resolve. For a drug like a proton-pump inhibitor, the standard counseling tends to focus on rebound acid hypersecretion. Whether the same conversation should include a longer conversation about microbial recovery isn't something most prescribers are trained to raise, and this study doesn't yet give them specific guidance on what to say if they did.

The researchers used a second stool sample from a sub-cohort of 328 participants collected roughly 4.4 years after the first, which gave the study more durability than a pure cross-sectional snapshot. That's a methodological strength worth noting, because much microbiome research leans on single time-point data and draws conclusions that don't hold up at follow-up.

The clinical translation is still early. Gastroenterologists and primary care physicians don't yet have a protocol that says: patient on long-term benzodiazepines, here's how you monitor or restore microbial balance after discontinuation. But the study does move the conversation from 'only antibiotics do this' to 'a lot of what we prescribe does this, and we should probably know it when we're deciding how and whether to deprescribe.'

Sources cited:
- ScienceDaily (University of Tartu / Estonian Research Council) (https://www.sciencedaily.com/releases/2026/08/260824065605.htm)
- mSystems / NCBI (commentary by Pamela Ferretti, University of Chicago) (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12542764/)
- The Scientist (https://www.the-scientist.com/medication-use-associated-with-gut-microbiome-changes-years-later-73530)