It may lead to medicines being less effective.

Researchers write that in the magazine Nature. They rely on experiments.


When we take medicines orally, they also end up in the intestines. And there they are met by a wide range of gut bacteria. That it results in an interaction between those bacteria and the medication is not new. Previous research has already shown that some bacteria alter the drugs slightly. This is also known as biotransformation.

Accumulated in bacteria

But new research now shows that something else can also happen in our gut. Certain types of gut bacteria appear to absorb our medication. The medication thus accumulates in these bacteria and changes their activity. It can also lead to a change in the composition of our microbiota (the complete collection of microorganisms that live in our gut).


The fact that bacteria absorb medication may have an influence on the effectiveness of drugs, the researchers say. Because when bacteria ‘snack’, there is less left for us and the medicines may also work less well. But the fact that bacteria absorb our medication can also affect our health in a completely different way. For example, the altered activity of bacteria or the composition of the microbial community in our gut due to the medication can lead to certain side effects.


The researchers base their conclusions on experiments. They cultured 25 common types of gut bacteria and exposed them to 15 drugs taken orally. Consider, for example, antidepressants, which have already been shown to work better in some than others and can also cause side effects such as weight gain and intestinal problems. During their experiments, the researchers encountered 70 interactions between the bacteria and the studied medication. 29 of those interactions were unknown until recently. And 17 of these 29 new interactions involved situations in which the bacteria took the medication – inappropriately.


It is surprising that most of the new interactions involved the absorption of drugs in bacteria, according to researcher Kiran Patil. “Until recently, it was thought that bacteria influence drug availability primarily through biotransformation.” In addition to duloxetine (an antidepressant), the bacteria also took rosiglitazone (a medicine for diabetes) in the experiments. And for some drugs — including asthma drug montelukast and lung drug roflumilast — researchers even witnessed them being modified by some bacteria and absorbed by others.

Proven Effects

Additional experiments also show that the absorption of medication has an influence on the bacteria. For example, the metabolism of bacteria that absorbed duloxetine appeared to change. And the metabolic products that these bacteria release again and that are consumed by other bacteria also changed. As a result, the bacteria consuming these metabolic products grew faster and the composition of the microbial community was disrupted.

A new organ

“It is only now that people are beginning to realize that medicines and our microbiome interact with each other and that this has important consequences for our health,” said researcher Athanasios Typass. His colleague Peer Bork even goes a step further. “It’s time to start treating the microbiome as one of our organs.”

More research is desperately needed, says Patil. “After this basic molecular research, we need to take the next step and find out how an individual’s gut bacteria are related to individual-to-individual responses to drugs such as antidepressants.” This does not only concern differences in the effectiveness of the drugs (they work better with some people than with others), but also differences in doses (one needs more than the other) and differences in side effects. “If we can determine how people react – depending on the composition of their microbiome – then we can start tailoring treatments.”