Evidence Level
Moderate
L-Tryptophan has been used for decades as a sleep and mood aid. Its ability to reduce sleep latency is well-documented, though effects on total sleep time are less consistent. The 1989 eosinophilia-myalgia syndrome (EMS) outbreak was traced to a contaminated batch from a single manufacturer, not to tryptophan itself — modern pharmaceutical-grade products are considered safe. Compared to 5-HTP, tryptophan is gentler but also supports the kynurenine pathway.