Evidence supporting the use of: L-theanine
For the health condition: Mental Illness

Links: Go back one page, Tool main page, Ingredients list, Health conditions list, Body systems list

Synopsis

Source of validity: Scientific
Rating (out of 5): 3

L-theanine is an amino acid commonly found in tea leaves, particularly green tea. Its use for supporting mental health is grounded in scientific research, though the evidence is moderate rather than definitive. Several randomized controlled trials (RCTs) and systematic reviews have examined L-theanine’s impact on mental health, especially its effects on anxiety, stress, and cognitive function. L-theanine appears to increase alpha brain wave activity, which is associated with a state of relaxed alertness. Studies have shown that L-theanine supplementation can reduce self-reported stress and anxiety in both healthy individuals and those with mild anxiety symptoms. For example, a 2019 systematic review in Phytotherapy Research concluded that L-theanine may help reduce stress and anxiety in people exposed to stressful conditions. Additionally, some small studies suggest potential benefits for symptoms of depression and for improving sleep quality, both of which are relevant to mental illness.

However, while these findings are promising, most studies to date are small, short-term, and sometimes use mixed formulations (e.g., L-theanine with caffeine). There is less evidence for L-theanine as a primary treatment for major psychiatric disorders such as major depressive disorder or schizophrenia, though adjunctive studies are beginning to emerge. Overall, L-theanine is considered safe and well-tolerated, which supports its use as a supplementary approach for mild mental health symptoms, but more high-quality research is needed to clarify its role in treating clinical mental illness.

More about L-theanine
More about Mental Illness