L-Theanine for Sleep Quality

A 2025 review analyzed multiple trials on L-theanine, an amino acid found in tea. It found that L-theanine improved sleep quality. L-theanine is thought to act as a competitor to glutamate, the brain’s main excitatory neurotransmitter, and it may increase GABA, the brain’s main inhibitory neurotransmitter. However, L-theanine may not necessarily improve anxiety. L-theanine may cause digestive or other side effects.

Cotter J, Caddick CE, Harper JL, Ebajemito JK. Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials. Nutr Neurosci. 2026 Feb;29(2):224-238. doi: 10.1080/1028415X.2025.2556925. Epub 2025 Nov 1. PMID: 41176609.

Sarris J, Byrne GJ, Cribb L, Oliver G, Murphy J, Macdonald P, Nazareth S, Karamacoska D, Galea S, Short A, Ee C, Birling Y, Menon R, Ng CH. L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trial. J Psychiatr Res. 2019 Mar;110:31-37. doi: 10.1016/j.jpsychires.2018.12.014. Epub 2018 Dec 8. PMID: 30580081.