A 2025 systemic review published in BMC Psychiatry involving 34 clinical trials and more than 3,300 people found that depression symptoms could be effectively treated by targeting gut bacteria with the use of probiotics (beneficial bacteria), prebiotics (nutrients that feed good bacteria) and synbiotics (a combination of both). The therapies were shown to reduce depression scores, increase levels of BDNF (an important protein for brain health) and mitigate systemic inflammation.

Notably, synbiotics exhibited the most pronounced effectiveness, followed by prebiotics and probiotics. Treatment for longer than 12 weeks was not considered helpful. Those without other medical conditions fared better, while individuals with digestive disorders and pregnant women did not experience the benefits. These findings suggest that enhancing gut health may be a useful complementary tool for depression management.