Psychobiotics is a term used in preliminary research to refer to live bacteria that, when ingested in appropriate amounts, might confer a mental health benefit by affecting microbiota of the host organism.^[1] Whether bacteria might play a role in the gut-brain axis is under research. A 2020 literature review suggests that the consumption of psychobiotics could be considered as a viable option to restore mental health^[2] although lacking randomized controlled trials on clear mental health outcomes in humans.^[3][4]

This article needs more reliable medical references for verification or relies too heavily on primary sources. (December 2018)

In experimental probiotic psychobiotics, the bacteria most commonly used are gram-positive bacteria, such as Bifidobacterium and Lactobacillus families, as these do not contain lipopolysaccharide chains, reducing the likelihood of an immunological response.^[1] Prebiotics are substances, such as fructans and oligosaccharides, that induce the growth or activity of beneficial microorganisms, such as bacteria on being fermented in the gut.^[1][5] Multiple bacterial species contained in a single probiotic broth is known as a polybiotic.^[6]

A 2021 review showed that treating anxiety in young people with psychobiotics had no significant effect.^[7] There is a need for more diverse human studies, mainly because those that exist have contradictory outcomes.^[3][4][7]