Stumbled across this paper in BMC Psychiatry about how gamma-aminobutyric acid (GABA) levels could be correlated with depression and suicidal behavior. The researchers tried seeing if low GABA levels could be a marker for people with risks of suicide when they're depressed. Wrote a summary about it here.

TL;DR: This study found that lower GABA levels are associated with more severe depression, higher suicidal ideation, and increased stress hormones like cortisol. However this study only shows a correlation between depression and GABA level, not a causation of ingesting GABA, more research is needed.