New research has shown, for the first time, how mixtures of commonly used medications that end up in our waterways and natural environments might increase the development of antibiotic-resistant bacteria.

When humans or animals take medications, as much as 90% can pass through the body and into natural environments, via waste water, or run-off from fields, ending up in the ocean.

In the environment, this build-up of antibiotic medicines can accumulate to a strength sufficient to kill the bacteria that live there. This can result in bacteria evolving defenses that help them to survive these concentrations, which can mean they are also resistant to antibiotics used to treat them if they later infect humans.

However, less is known about how the build-up of other medicines also affects bacteria, and until now, scientists have largely investigated the effect of these medications on triggering this antibiotic resistance one-at-a-time.

Now, new research led by the University of Exeter and published in the journal ISME Communications, has revealed that regular drugs used for pain relief, diabetes medication, and hormone replacement can increase the tendency for bacteria to develop the genes needed to resist antibiotic treatments, when combined with a common antibiotic as happens in the environment.