Free form amino acids, particularly those like tryptophan, tyrosine, and phenylalanine, have been studied for their potential role in depression because they are precursors to neurotransmitters such as serotonin, dopamine, and norepinephrine. The rationale is that deficiencies or imbalances in these neurotransmitters are associated with depressive symptoms, so supplementing with precursor amino acids may help alleviate depression. Some clinical trials have shown modest improvements in depressive symptoms with supplementation, especially in individuals with mild to moderate depression or those with low baseline levels of these amino acids. However, the evidence is inconsistent and often limited by small sample sizes, short durations, or lack of rigorous controls. Reviews and meta-analyses generally conclude that while there is a biochemical basis for the use of certain amino acids in mood disorders, the clinical efficacy is not robustly established compared to standard antidepressant therapies. Therefore, free form amino acid supplementation is sometimes used as an adjunct or alternative therapy, but it is not considered a first-line or well-validated treatment for depression. More research is needed to clarify which subgroups may benefit and to establish appropriate dosing and safety profiles.