Background: Studies on the effects of microorganisms living in the guts of human health
and the etiopathogenesis of diseases, especially psychiatric disorders, have rapidly increased in recent
years. According to the results of these studies, evidence has been found that there is direct and
indirect (immune system) interaction between the microbiota bacteria and their metabolites and
Objective: The purpose of this review is to discuss the current research findings focusing on the
relationship between the gut microbiota and psychiatric disorders. In this context, the effectiveness
of microbiota-based treatments (probiotics and fecal microbiota transplantation) on the treatment of
psychiatric disorders is also discussed.
Method: A review of the literature was conducted that includes the following words: gut-brain axis,
microbiota, dysbiosis, psychiatry and mental disorders.
Results: There are few clinical studies examining the gut-brain relationship. In the light of the evidence
from these clinical trials and animal experiments, it can be suggested that gut microbiota has a
distinct and determinative role in brain function.
Conclusion: Gut microbiota creates a determining and life-long effect on the emergence of the immune
system and the brain in the fetus starting with birth. Delivery mode, breastfeeding, diet, drugs
(antibiotics, psychotropics) and aging may change the composition of gut microbiota. Disruption of
microbiota composition (dysbiosis) may lead to the emergence of psychiatric disorders. Microbiotabased
treatments have a therapeutic potential by repairing dysbiosis. There is a need for more randomized
controlled studies in order for the effects of gut microbiota on psychiatric disorders to be