Impact of L-theanine and L-tyrosine on markers of stress and cognitive performance in response to a virtual reality based active shooter training drill

McAllister MJ, et al.

Published in Stress

Methodology

Randomised placebo-controlled trial (NCT05592561) in 80 adults given a single dose of L-tyrosine 2,000 mg, L-theanine 200 mg or placebo before a mental stress challenge comprising Stroop and mental arithmetic tasks plus a virtual reality active shooter training drill; saliva (alpha-amylase, secretory IgA), state-anxiety inventory and heart rate measured before and after.

Key Findings

Eighty adults (average age 21, 46 male and 34 female) were randomly given L-tyrosine 2,000 mg (n = 28), L-theanine 200 mg (n = 25) or placebo (n = 27) before a mental stress challenge combining a Stroop task, mental arithmetic and a virtual-reality active shooter drill. The challenge itself significantly raised salivary alpha-amylase, secretory IgA, heart rate and state anxiety, confirming it produced real stress. Neither L-theanine nor L-tyrosine had any effect on these stress markers, a clear null result. L-tyrosine did produce significantly fewer missed responses than placebo on the Stroop challenge, suggesting a narrow cognitive rather than stress-buffering effect.

Conclusions

Ingestion of L-theanine or L-tyrosine does not impact markers of stress in response to a mental stress challenge but may impact cognitive performance.

Limitations

A single acute dose in about 27 young healthy adults per arm, with one favourable cognitive outcome among several measured, so the Stroop result could be chance; findings say nothing about ongoing daily use or about older or chronically stressed people.