In this 2015 systematic review that assesses the effectiveness of tyrosine supplementation in healthy adults on improving cognitive or physical performance under stress, ten randomized controlled trials and four controlled clinical trials were included. Of the six studies examining tyrosine on cognition during stressful situations that deplete catecholamines (sleep deprivation, extreme climate conditions, military combat training) – all six demonstrated some benefit on several psychological parameters (assessing attention, reaction time, memory.)
Attipoe S, Zeno SA, Lee C, Crawford C, Khorsan R, Walter AR, Deuster PA. Tyrosine for Mitigating Stress and Enhancing Performance in Healthy Adult Humans, a Rapid Evidence Assessment of the Literature. Mil Med. 2015 Jul;180(7):754-65. doi: 10.7205/MILMED-D-14-00594. PMID: 26126245.