New Trial Establishes Safe Daily L-Tyrosine Intake for Healthy Adults

A four-week course of L-tyrosine supplementation appears to be safe and well-tolerated in healthy adult men, according to a new study published in the journal Nutrients.

L-tyrosine is an amino acid naturally found in protein-rich foods such as meat, dairy products, and soy. It plays an important role in the production of neurotransmitters involved in mood, attention, and stress responses. While previous studies have suggested potential cognitive and stress-related benefits of L-tyrosine, data on its long-term safety at different doses have been limited.

To address this gap, researchers in Japan conducted a randomized, double-blind, placebo-controlled trial involving 30 healthy men aged 20 to 60 years. Participants received placebo or L-tyrosine supplements at doses ranging from 1 to 4 grams per day for four weeks, with washout periods between treatment phases.

The researchers monitored a wide range of health measures, including liver and kidney function, blood cell counts, cholesterol levels, blood sugar, electrolytes, and other biochemical markers. They also tracked adverse events, dietary intake, body measurements, and blood amino acid levels throughout the study.

Results showed no significant differences between any L-tyrosine dose and placebo for clinical safety markers. Liver function, kidney function, blood counts, and metabolic measures remained stable across all treatment groups. Although 18 mild or moderate adverse events were reported during the study, no serious adverse events occurred, and researchers found no evidence of a dose-related increase in side effects.

Based on the findings, researchers concluded that daily L-tyrosine supplementation of up to 4 grams for four weeks produced no observable adverse effects in healthy adult men. However, they noted that larger studies involving women, individuals with medical conditions, higher doses, and longer follow-up periods are needed to fully evaluate its long-term safety.

REFERENCE: Matsumoto H, Miura N, Naito M, Elango R (2026). Evaluation of the Safety and Tolerability of L-Tyrosine Supplementation in Healthy Adult Men: A Randomized Crossover Trial. Nutrients, 18(12), 2020. DOI: 10.3390/nu18122020, https://www.mdpi.com/2072-6643/18/12/2020