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