L-Threonine
Threonine is an essential amino acid: the body cannot make it and needs it from food to build proteins.
Also listed as Threonine
A newer human study, with clear boundaries
A 2025 controlled trial tested graded doses up to 12 g daily, each for four weeks, in 30 healthy Japanese men. No serious adverse events were reported. The highest tested dose was identified as a no-observed-adverse-effect level for this experiment, not a general upper limit. Manufacturer employees were among the authors. 1
Who was outside that study?
The trial excluded people with several medical conditions, including kidney, liver and intestinal disease. It cannot establish safety for those groups, pregnancy, children or prolonged use. BfR also cautions that high additional amounts of individual amino acids can cause unwanted effects. 1 2
For information, not individual medical advice. Ingredient studies do not establish the effectiveness of these products.