Theanine (L-Theanine) is an amino acid derivative and often formulated from L-glutamine. Theanine is found naturally, and almost exclusively, in tea (Camellia sinesis), where it constitutes about 1–2% of the dried leaves.

Major Health Benefits

L-Theanine may aid in decreasing stress response as well as cognitive impairments in stressful situations.1,2 Consumption of L-Theanine along with caffeine may improve cognitive function by increasing acuity and alertness while reducing self-reported tiredness.3 A lab study reported that inhibiting death of nerve cells may be the mechanism of neuroprotective effect by L-Theanine.4 The calming effects of L-Theanine may also positively affect cognition.5 It has been suggested in some studies that L-Theanine may aid in promoting normal sleep in patients with schizophrenia and in boys with attention deficit hyperactivity disorder (ADHD).1,6


  1. Ota M, Wakabayashi C, Sato N, Hori H, Hattori K, Teraishi T, Ozawa H, Okubo T, Kunugi H. Effect of l-theanine on glutamatergic function in patients with schizophrenia. Acta Neuropsychiatr. 2015 Apr 21:1-6. PMID: 25896423.
  2. Unno K, Tanida N, Ishii N, Yamamoto H, et al. Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary α-amylase activity, trait anxiety and subjective stress. Pharmacol Biochem Behav. 2013 Oct;111:128-35.PMID: 24051231.
  3. Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010 Dec;13(6):283-90.PMID: 21040626.
  4. Kakuda T. Neuroprotective effects of theanine and its preventive effects on cognitive dysfunction. Pharmacol Res. 2011 Aug;64(2):162-8. PMID: 21477654.
  5. Kelly SP, Gomez-Ramirez M, Montesi JL, Foxe JJ. L-theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance. J Nutr. 2008 Aug;138(8):1572S-1577S.PMID: 18641209.
  6. Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev. 2011 Dec;16(4):348-54.PMID: 22214254.