In a new study, researchers found that antidepressants and other psychiatric drugs can change the quantity and composition of gut bacteria.
These results raise questions about the specificity of psychoactive drug action.
The research was conducted by a group of Irish-based scientists.
Scientists are increasingly finding that the microbiome—the bacterial content of the digestive system—has effects on other functions in the body, and vice versa.
In the study, the team tested 7 groups of rats (8 animals in each group). These rats received normal or slightly elevated levels of individual psychopharmaceuticals, including Lithium, valproate, and the antidepressants fluoxetine (Prozac) and escitalopram.
After 4 weeks of treatment, the scientists examined the gut bacteria—the microbiome—to see what the effects the drugs had.
They found that some drugs consistently increased the number of certain bacteria in the gut.
For example, lithium and valproate (both used for bipolar disorder) increased the numbers of Clostridium and other bacteria.
In contrast, the (SSRI) antidepressants escitalopram and fluoxetine significantly inhibited the growth of bacterial isolated strains such as E.coli.
The findings show that certain drugs, including the mood stabilizer lithium and the antidepressant fluoxetine, influenced the composition and richness of the gut microbiota.
Although some psychotropic drugs have been previously investigated in vitro settings, this is the first evidence in an animal model.
The team says some previous studies have shown that depressed or schizophrenic patients can have altered microbiota composition, therefore psychotropic drugs might work on intestinal microbes as part of their mechanisms of action.
If confirmed in humans, psychiatrists might need to consider the effects on the body before prescribing.
The research team is currently carrying out a large-scale human observational study which aims to answer the questions posed by these findings.
The lead author of the study is Ms. Sofia Cussotto (University College).
The study is presented at the ECNP Conference in Copenhagen following part-publication in a peer-review journal.
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