L-Theanine is an amino acid found primarily in green tea (but also in other types). And it’s the reason why tea, even though it has caffeine, won’t give you the jitters or the mid afternoon crash.
L-theanine elevates levels of GABA, as well as serotonin and dopamine. These chemicals are known as neurotransmitters, and they work in the brain to regulate emotions, mood, concentration, alertness, and sleep, as well as appetite, energy, and other cognitive skills.
L-theanine also reduces levels of chemicals in the brain that are linked to stress and anxiety. This may also be a way that L-theanine can protect brain cells against stress and age-related damage.