There are a number of reasons why tea is good for you: the antioxidant content is incredible, for instance, and it decreases risk of stroke, diabetes, cholesterol, obesity, hypertension, and even depression. But it also contains an excellent nootropic (substance that enhances cognition): L-Theanine.

L-Theanine’s Biochemical Cousins

Protein (one of the three major macronutrients) is made from twenty foundational amino acids. L-Theanine is not one of them, but it is derived from glutamine (which is). Glutamine can also convert into two amino acid neurotransmitters, glutamate and GABA. Glutamate and GABA share a receptor, called the NMDA receptor, though glutamate stimulates the receptor while GABA calms it down. Since L-Theanine is a biochemical cousin to glutamate and GABA, in order to understand how it works, we first need to understand how they work.

Glutamate is the primary excitatory neurotransmitter in the body, acting both on motor neurons for movement, and also on the neurons responsible for learning and memory. Too much stimulation to glutamate’s NMDA receptor leads to excitotoxicity, and GABA, the neurotransmitter affected by both alcohol and benzodiazepines (the principle class of anti-anxiety meds), is responsible for shutting this process down.

L-Theanine’s Unique Effects on Anxiety and Focus

What makes L-Theanine a bit strange is that, while it is generally calming like GABA, it appears to act as an agonist (stimulant) to the NMDA receptor, just like the excitatory neurotransmitter glutamate. It also protects against neurotoxicity from excess dopamine, the primary neurotransmitter associated with focused concentration. In this way, it helps to mitigate both of the major types of anxiety, biochemically speaking: excess dopamine, and excess glutamate.

Yet unlike alcohol and benzos, L-Theanine manages to decrease anxiety in such a way that it simultaneously increases focus. It’s like a buffer in that way, preventing both high highs and low lows. It increases alpha frequency waves in the brain: these are associated with relaxed concentration. It works even better when combined with caffeine: this study shows that the potent combo of L-theanine and caffeine (like what you’d get from tea) particularly improves cognitive performance.

L-Theanine’s Effects on Mood

At the same time, L-Theanine readily crosses the Blood Brain Barrier, and according to this study, stimulates the release of both serotonin and dopamine. Low levels of each of these are responsible for two different types of depression: low serotonin depression is probably best known (as it is most often treated with SSRIs such as Prozac), but low catecholamine depression is also quite common. The latter can be difficult to treat in people who also have simultaneous anxiety, since giving catecholamine precursors for dopamine can also worsen anxiety symptoms, if the anxiety is of the high dopamine variety.

Fortunately, L-Theanine offers a way around that quandary. It’s balancing. You get the best of both worlds. 

The Upshot:

It might sound like I’m saying L-Theanine is a panacea for neurotransmitter imbalance, but that’s not quite true. In some cases, other choices might be better (if there’s a pure catecholamine deficiency, for instance, or too little GABA, or too little serotonin). But for mixed cases, particularly where greater concentration and focus is desired, L-Theanine is a great choice.

L-Theanine can be found in both black and green tea, though the levels are higher in the former: about 24 mg per cup of black tea, and 8 mg per cup of green tea. These levels are still pretty low, so you might wish to supplement to maximize its effects. I generally recommend starting at 100 or 200 mg daily.