A new study in the journal Chirality suggests that dietary supplements that do not use pure L-theanine may not deliver the expected benefits. Researchers from an Iowa State University (ISU) study compared the pharmacokinetics of L-theanine, D-theanine, and an ingredient commercially marketed as "L-theanine' that actually was a racemic mixture of theanine (a 50:50 D- and L-theanine mixture, also known as a racemate).
The research team orally supplemented rats with three different theanine ingredients: a commercially available "L-theanine" that actually was a racemate, pure D-theanine and pure L-theanine. They then followed blood concentrations, urinary excretion and a marker of theanine metabolism in the blood.