DrG's Medisense Feature Article

Theanine
By Ann Gerhardt, MD
March 2025
Print Version

Theanine is an amino acid, but not one that is a building block for the body’s proteins.  Because it is not made in our bodies, it has become a popular supplement used to improve cognitive function, calm mood, and reduce anxiety related to stress.  However, it won’t cure-what-ails-you, like other over-hyped supplements and is not essential for survival.

The only natural source would be food, with the best options being white, Oolong, black and green (especially gyokuro, macha, and sencha) teas, most mushrooms and nori and wakame seaweed.  Minor food sources are soy products, barley, oats and dark chocolate (Yeah!). 

In mouse studies, l-theanine augmented alpha brain wave activity and suppressed inflammation- induced glutamate release and cell death in the brain (both good things) and boosted levels of the brain hormones GABA (gamma-amino butyric acid), dopamine and serotonin. 

In humans, these brain hormones would likely improve mood.  Studies in both mice and humans demonstrate that chronic consumption of a large, single daily dose improves short-term memory, reaction time and attention to a task.   Japanese studies suggest that chronic ingestion improves humans’ age-related memory impairment and other studies have documented reduced anxiety.  It has been well-tolerated in both large single dose and chronic moderate dose human studies.

From these studies it appears that theanine is another good reason, in addition to reducing chronic Western Society diseases, to try being vegetarian, consuming a wide variety of plant foods, including those listed above.

In summary, with or without a theanine supplement, try oats for breakfast, mushroom salad for lunch, tea and dark chocolate mid-afternoon, and barley soup for dinner, to perhaps improve sleep and remember your grandkids’ names and why you entered that room.