N-Acetyl-L-Tyrosine

NALT is L-tyrosine with an acetyl group attached to its amino group. That modification improves solubility and makes the compound convenient for liquid products and parenteral nutrition, where free tyrosine is difficult to formulate. The practical formulation advantage is real; the claim that NALT efficiently turns back into tyrosine in people is much shakier.

In 11 healthy volunteers given 5 g intravenously over four hours, plasma tyrosine rose only 25%, 56% of the NALT appeared unchanged in urine within four hours, and the authors found no clear usefulness as a tyrosine precursor [1]. Another experiment found that plasma tyrosine did not rise in either healthy people or dialysis patients and that healthy controls excreted about 60% unchanged [2]. The same failure to raise tyrosine occurred in people with hepatic failure [4].

A routine parenteral-nutrition study was less negative: 13 adults excreted about 35% unchanged, leaving enough aromatic amino acid from NALT plus phenylalanine to meet estimated needs [3]. That does not show superiority to free tyrosine or efficacy for cognition. No human oral efficacy study was found for this entry.

NALT must be deacetylated to release free L-tyrosine before it can contribute to catecholamine synthesis. Human balance studies suggest that this step is inefficient: clearance is low, urinary loss is high, and plasma tyrosine often does not increase [1][2][4].

The oral evidence is even thinner. In a mouse comparison of several tyrosine prodrugs, NALT was the least effective at raising brain tyrosine [5]. That animal result cannot quantify oral availability in humans, but it gives no support to claims of enhanced brain delivery.

NALT contains 181.19 g of tyrosine moiety per 223.22 g of compound, so an equal milligram dose contains about 19% less tyrosine even before metabolic losses. Its value is solubility, not demonstrated potency. Intravenous human studies show that a substantial fraction remains acetylated and is excreted [1][3].

The small infusion studies were designed around metabolism and nutrient retention, not long-term safety or oral supplement use. They document exposure in healthy volunteers, dialysis patients, people with hepatic failure and adults receiving parenteral nutrition [1][2][3][4], but they do not establish chronic oral safety.

Renal handling matters because unchanged NALT is a major urinary product. Clearance was lower in dialysis patients [2] and in people with hepatic failure [4], even though neither group showed a useful rise in plasma tyrosine.

No direct interaction studies were found. NALT should not be assumed to escape the cautions relevant to tyrosine merely because its conversion is incomplete, and its high renal loss makes advanced kidney disease a distinct uncertainty [2].