Acetyl-L-Tyrosine is a modified form of the amino acid L-tyrosine, which is a direct precursor to catecholamines such as dopamine, norepinephrine, and epinephrine (adrenaline) in the body. The rationale for using Acetyl-L-Tyrosine to support the "Epinephrine body system" stems from the role of tyrosine in the biosynthetic pathway of these neurotransmitters. Scientific studies show that supplemental L-tyrosine can increase catecholamine synthesis in situations where there is increased demand or depletion, such as during acute stress, sleep deprivation, or prolonged cognitive tasks. Some research has found that tyrosine supplementation may help maintain cognitive performance under stress, presumably by supporting catecholamine synthesis, including epinephrine. However, direct studies specifically on Acetyl-L-Tyrosine (as opposed to plain L-tyrosine) are limited, and evidence is not robust for routine use in healthy, non-stressed individuals.

The "Acetyl" modification is believed to improve bioavailability, but this has not been consistently demonstrated in clinical studies. Overall, there is scientific rationale and some supporting evidence for Acetyl-L-Tyrosine or L-tyrosine supplementation to support catecholamine (including epinephrine) levels during acute stress, but the quality and quantity of evidence specifically supporting its use for the epinephrine system is moderate at best.