Does Theanine Decrease Serotonin?

L-theanine is an amino acid derivative that is found rarely in nature, but is abundant in the leaves of the Camellia sinensis, or tea, plant. Recently discovered to be psychoactive, L-theanine has become the subject of research into its possible therapeutic utility in the treatment of conditions as varied as hypertension, cancer and psychiatric disorders. As research on this compound is only in its fledgling stages, there is as yet no conclusive evidence for its efficacy in the treatment of any condition. If you are considering taking L-theanine or any other supplement, first discuss it with your physician.


Serotonin is a neurotransmitter found both in the brain and throughout the body. It is responsible for the regulation of a complex variety of body systems, one of which is mood. It has long been presumed that since drugs that increase extra-cellular levels of serotonin treat depression, then elevated levels of serotonin in the brain produce elevated mood. With the approval of novel antidepressants such as tianepeptine, which treats drug-resistant depression by lowering synaptic levels of serotonin, this neurochemical model has been substantially eroded.

New Research

A new report from Johns Hopkins has presented an alternative model for the mechanism by which antidepressant drugs work, one which accounts for the unexplained four-to-six-week delay between initiating treatment and treatment efficacy. According to Dr. Vassilis Koliatsos, a neuropathologist with the clinic, "Serotonin reuptake modulators increase the density of nerve synapses, especially in the front part of the brain, which may offer a better explanation of why antidepressants are effective and why they take time to work. This disparity between simple pharmacological effects and clinical experience might be due to the time it takes for serotonin axons to grow." In other words, antidepressants may work not by increasing serotonin levels in the brain, but by rewiring the parts of the brain responsible for mood and motivation.


Although the research is conflicted on the effect of L-theanine on the levels of extra-cellular serotonin in the brain, this data may not be the most reliable indicator of L-theanine's effect on mood. Until studies are performed on the effect of L-theanine administration on the growth of serotonin axons in the frontal and parietal lobes of the neocortex and limbic system, the part of the brain that regulates motivation and emotion, then clinical studies will provide the best gauge of L-theanine's effect on depression. At present, while there are a number of studies that suggest that L-theanine may complement conventional treatments for anxiety disorders, there are none that support L-theanine's use in treating depression.


L-theanine has only recently begun to be used in as a treatment for psychiatric disorders. Consequently, you should talk to your doctor about the latest research on L-theanine and determine whether or not this supplement is right for you. L-theanine produces few side effects, the most common of which is headache, followed by dizziness and stomach upset. Consuming enough L-theanine to produce a toxic reaction is unlikely to occur in the course of normal use, according to The Food and Drug Administration, which does not claim that L-theanine is an effective treatment for any condition, does classify the compound as "generally recognized as safe."

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