Health Library Home>Natural & Alternative Treatments>Herbs & Supplements>Article


Supplement Forms/Alternate Names:

L-gamma-glutamylethylamide, theanine


L-Theanine is an amino acid that is found in black and green tea as well as some mushrooms. It has been used to ease feelings of anxiety and improve sleep. It can be taken as a pill, powder, or extract.


There are no advised doses for L-theanine.

What Research Shows

May Be Effective

  • Cancer Treatment Support —may ease side effects from chemotherapy A1
  • Insomnia in children with ADHD —may improve sleep efficiency and quality B1, B2
  • Mild cognitive impairment —may improve memory and attention when used with green tea extract C1
  • Schizophrenia —may ease anxiety D1, D2

Editorial process and description of evidence categories can be found at EBSCO NAT Editorial Process.

Safety Notes

It may be safe to take L-theanine for a short time, but it may lower blood pressure and cause headaches. Not enough studies have been done to say whether it is safe to take for a long period or if it is safe for women who are pregnant or breastfeeding.


Talk to your doctor about any supplements or therapy you would like to use. Some can interfere with treatment or make conditions worse.



A. Cancer Treatment Support

A1. Tsuchiya T, Honda H, et al. Oral administration of the amino acids cystine and theanine attenuates the adverse events of S-1 adjuvant chemotherapy in gastrointestinal cancer patients. Int J Clin Oncol. 2016 Dec;21(6):1085-1090.

B. Insomnia in Children with ADHD

B1. Lyon MR, Kapoor MP, et al. 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):348-354.

B2. Barrett JR, Tracy DK, et al. To sleep or not to sleep: a systematic review of the literature of pharmacological treatments of insomnia in children and adolescents with attention-deficit/hyperactivity disorder. J Child Adolesc Psychopharmacol. 2013 Dec;23(10):640-647.

C. Mild Cognitive Impairment

C1. Park SK, Jung IC, et al. A combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment: a double-blind placebo-controlled study. J Med Food. 2011 Apr;14(4):334-343.

D. Schizphrenia

D1. Ritsner MS, Miodownik C, et al. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study. J Clin Psychiatry. 2011 Jan;72(1):34-42.

D2. Kardashev A, Ratner Y, et al. Add-On Pregnenolone with L-Theanine to Antipsychotic Therapy Relieves Negative and Anxiety Symptoms of Schizophrenia: An 8-Week, Randomized, Double-Blind, Placebo-Controlled Trial. Clin Schizophr Relat Psychoses. Spring 2018;12(1):31-41.

Last reviewed March 2020 by EBSCO NAT Review Board Eric Hurwitz, DC  Last Updated: 6/22/2020