l-theanine

L-theanine is an amino acid found naturally in tea leaves (Camellia sinensis), the plant used to make green and black tea. It is sold on its own as a dietary supplement, usually in capsule or tablet form, and is also consumed through brewed tea.

These describe how people use L-theanine, not benefits proven by authoritative US government health sources. The NIH Office of Dietary Supplements and NCCIH do not currently publish a dedicated fact sheet evaluating isolated L-theanine supplements, so rigorous, government-vetted conclusions about whether it works are not available. NCCIH's page on green tea — the natural dietary source of L-theanine — does not address L-theanine on its own and cautions that, even for green tea overall, "definite conclusions cannot yet be reached on whether green tea is helpful for most of the purposes for which it is used." Treat any claimed benefit of isolated L-theanine as unproven.

There is no official US government recommended dose for L-theanine, and authoritative sources do not establish an effective amount; product strengths vary widely between brands. Because the evidence is limited, talk to a doctor or pharmacist before starting L-theanine, and do not use it as a substitute for medical evaluation or treatment of a condition such as anxiety or insomnia.

Authoritative US government sources do not provide a safety review specific to isolated L-theanine supplements, so its safety profile is not well established by these sources. As a general precaution, pregnant or breastfeeding people, children, and anyone with a health condition or taking medication should consult a clinician before use. Note that L-theanine is often paired with caffeine and that tea-derived products contain caffeine; NCCIH advises that caffeine intake should not exceed moderate levels during pregnancy and that anyone who is or might be pregnant should ask their health care provider about caffeine.

Government sources do not publish a side-effect profile specific to isolated L-theanine. Because L-theanine is frequently combined with caffeine and is naturally present in caffeinated tea, any caffeine-related effects (such as jitteriness, increased heart rate, or trouble sleeping) would generally come from the caffeine rather than the L-theanine itself. Because the safety of isolated L-theanine is not well characterized by authoritative sources, stop use and contact a healthcare provider if you have an unexpected reaction.

No authoritative US government source documents drug interactions for isolated L-theanine, so its interaction profile is not established. The interaction information below is for green tea, the food source of L-theanine, and not for the isolated amino acid: NCCIH reports that green tea can interact with certain medications, including reducing blood levels of nadolol (a beta-blocker) and atorvastatin (a cholesterol drug), and an NCCIH-funded study found an interaction between green tea and raloxifene. Tell your doctor or pharmacist about every supplement and medication you take so they can check for possible interactions.