Monoamine antidepressants convey secondary mechanisms that may alter gut microbiota and glutamate to impact MDD symptoms. MDD is associated with elevated glutamate levels in the frontal cortex. These antidepressants work to reduce glutamate signaling to prevent excitotoxicity. This effectively reduced NMDA functioning, increases AMPA signaling, which leads to BDNF production. In MDD, typically low BDNF levels are seen; this mechanism works to reverse this and attempt to effectively treat MDD.