L-theanine increases brain levels of several neurotransmitters
The amino acid l-theanine found in green tea is widely used in China, Japan, and other Asian countries to treat anxiety and depressed mood. Animal studies confirm that l-theanine increases brain levels of serotonin, dopamine, and gamma-amino-butyric acid (GABA) (an important inhibitory neurotransmitter) and may have general neuroprotective effects.
L-theanine reduces anxiety by increasing alpha brain wave activity
Anxiety-reducing effects of l-theanine are believed to be mediated by enhanced alpha brain wave activity in the occipital and parietal regions that are dose dependent and similar to EEG changes observed during meditation. Calming effects may last 8 to 10 hours and are usually experienced within 30 minutes following ingestion of l-theanine at doses between 50 and 200 mg.
Promising research findings need to be confirmed
However, findings of clinical research studies on l-theanine in anxiety are inconsistent. In one small placebo-controlled study (16 patients), healthy adult volunteers randomized to the prescription medication alprazolam (1 mg) versus l-theanine (200 mg) or placebo experienced equivalent and non-significant anxiety reducing effects during an experimentally induced anxiety state. In another small placebo-controlled study (12 patients), individuals taking l-theanine experienced relatively greater reduction in acute stress response as measured by changes in heart-rate variability (HRV) and salivary immunoglobulins (s-IgA) compared to the placebo group. These findings suggest that stress-reducing effects of l-theanine may be mediated by inhibition of cortical neuron excitation. In a crossover study, healthy adults were randomized to l-theanine (250 mg) alone or in combination with caffeine (150 mg). Compared to the l-theanine–only group, the combination group experienced improved visual information processing, reduced mental fatigue, faster reaction time and faster working memory, generally increased alertness, and fewer headaches. Moderately severe anxiety symptoms may respond to l-theanine taken at a dose of 200 mg twice daily however more severe anxiety may require doses up to 600 to 800 mg per day divided into 200-mg increments every 3 to 4 hours. Large well designed placebo-controlled studies on l-theanine are needed before more definitive comments can be made about its anti-anxiety benefits.
No safety problems
l-Theanine is generally well tolerated, and there are no published reports of serious adverse side effects or interactions with other natural products or conventional prescription medications