Theanine

Theanine is a non-protein amino acid analogue of glutamate and glutamine, and is found primarily in particular plants, especially teas, but also in some mushrooms.

Theanine is present in many plants commonly ingested, and along with caffeine is a principal component of the effects of green and black tea. Theanine can enter the brain, and has been demonstrated to increase the levels of several neurotransmitters*, including GABA, glycine, serotonin, and dopamine. Theanine is similar in structure to the excitatory neurotransmitter glutamate, and theanine has a complex relationship with glutamate receptors, stimulating some while blocking others.* Theanine is often used to promote relaxation without causing drowsiness.*

Theanine is not required for humans and dietary deficiency does not exist.

L-theanine has been studied for its potential ability to reduce mental and physical stress*, and in this context, it is typically used as a dietary supplement. A randomized-controlled trial found theanine “may assist in the reduction of stress… in people exposed to stressful conditions.”* [https://pubmed.ncbi.nlm.nih.gov/31758301/] Theanine is also often used to support cognition and focus*, an effect of tea drinking that is not solely related to the caffeine content.

Theanine is water-soluble and considered to be generally non-toxic. Theanine might lower blood pressure, and thus is a potential concern in those with hypotension. However, side effects are rare at usual doses used in supplementation.

Laboratory testing is neither available nor clinically useful.