10/10/2026
L-theanine is a naturally occurring amino acid found in green tea that may influence brain chemicals involved in stress, attention, mood, and relaxation, including GABA, dopamine, and glutamate. A 2024 systematic review published in BMC Psychiatry investigated whether L-theanine supplementation could improve symptoms in people with mental health disorders. Researchers screened 419 publications and selected 11 randomized controlled trials conducted across six countries, including the United States, Japan, Australia, Iran, Israel, and Italy. The studies examined conditions such as schizophrenia, ADHD, anxiety disorders, depression, OCD, sleep disorders, and Tourette syndrome, with L-theanine sometimes used alongside prescribed psychiatric medications.
The review found promising evidence that L-theanine could help reduce certain psychiatric symptoms, particularly in people with schizophrenia, anxiety disorders, and ADHD. The clinical trials used different doses depending on the condition, including approximately 250–400 mg daily for schizophrenia, 400 mg daily for ADHD, and 450–900 mg daily in a generalized anxiety disorder trial. Some studies reported improvements in anxiety-related symptoms, attention, and other measures of mental health, although results were not consistently positive across all conditions. Importantly, the generalized anxiety disorder trial did not demonstrate a significant advantage over placebo on its primary anxiety outcome. Researchers concluded that L-theanine may have potential as a supportive treatment, but larger, longer clinical trials are needed to establish its effectiveness, optimal dosage, and long-term safety.
PMID: 39633316
