N-Acetyl-L-Tyrosine (NALT)
N-Acetyl-L-Tyrosine (NALT) is a unrated form of L-Tyrosine, used in 933 on-market products .
Basis: Tyrosine C9H11NO3 (181.19) / N-acetyl-L-tyrosine C11H13NO4 (223.23) = 0.812, anhydrous free acid; stoichiometric tyrosine content only, NOT adjusted for absorption or conversion
Why this tier: No verified oral human comparison with free tyrosine. The only human data located were intravenous: in healthy volunteers and hemodialysis patients plasma tyrosine did not rise after infused N-acetyltyrosine (unlike alanyl- and glycyl-tyrosine), and about 60% of the infused amount was excreted in controls -- parenteral nutrition findings that do not directly transfer to oral supplements.
Source: Druml W et al. 1991, Am J Physiol 260(2 Pt 1):E280-E285, PMID 1996632 (intravenous, not oral)