The Brain Health Benefits of L-Theanine 

Cups of Green Tea

L-theanine is an amino acid found in tea. Since its discovery, there have been numerous studies that have found potential mental health benefits with its consumption. Some of the benefits provided by L-theanine appear to be related to its effects on brain neurotransmitters. 

Due to its relationship with depression, most people have heard of the neurotransmitter serotonin, often described as a “feel-good” neurotransmitter. Many antidepressants work through targeting serotonin.

L-theanine works mainly through a different neurotransmitter: glutamate. As a neurotransmitter, glutamate is excitatory, increasing certain types of activity throughout the brain. While a gross oversimplification, you can think of glutamate as a “feel-bad” neurotransmitter. When you consume L-theanine, it blocks glutamate activity, reducing its negative effects.   

Beyond effects on glutamate, L-theanine appears to impact other neurotransmitters and increase production of brain protective compounds. These effects may be relevant for helping to prevent Parkinson’s disease and Alzheimer’s dementia. 

Research suggests that L-theanine may be helpful for:

  • Stress, anxiety and insomnia
  • Depression
  • Schizophrenia
  • Parkinson’s disease and Alzheimer’s dementia

L-Theanine, Stress, Anxiety and Insomnia

The main function of the neurotransmitter glutamate is to speed up brain activity. L-theanine, by blocking glutamate, slows down brain activity. This has potential benefits for conditions related to increased brain activation from stress or anxiety. Studies in stressed individuals have mostly shown benefits with L-theanine. A small human study found that L-theanine has anti-stress effects, mostly through decreasing the stress response in the brain (Kimura 2007). A separate small study in older individuals found that L-theanine supplementation decreases stress-related symptoms, improves cognition and supports sleep (Hidese 2019). Other studies have shown similar results (White 2016, Yoto 2021).

While a small study on generalized anxiety disorder only found benefits for sleep, it’s probably not the end of the story for L-theanine’s effects on clinical anxiety (Sarris 2019). Other studies have found benefits for anxiety symptoms in patients with depression and schizophrenia, suggesting anxiety-reducing activity (Hidese 2017, Miodownik 2011).

L-Theanine and Depression

While L-theanine is known more for helping with stress, data is beginning to emerge suggesting benefits for depression. Studies on tea have found a reduced risk of depressive disorders and low mood with increasing tea consumption (Dong 2015). While it’s likely due to a number of different constituents found in tea, L-theanine may play a role (Rothenberg 2019).

In one clinical study of patients struggling with major depression, L-theanine was found to reduce depression and anxiety while improving sleep and cognitive performance (Hidese 2017). Animal studies also appear to confirm the antidepressant effects of L-theanine (Unno 2020, Shen 2019), although further human studies are warranted. 

L-Theanine and Schizophrenia 

Schizophrenia is often seen as a devastating illness that includes a combination of delusions, hallucinations, disorganized speech and problems with social functioning. The condition is difficult to manage, often with profound residual symptoms even with the use of antipsychotic medication. Additional tools and treatments, especially with a low-risk of side effects, are needed. 

One small trial combined L-theanine with standard medication and found that L-theanine improved symptoms of schizophrenia when added to standard medication (Ota 2015). Two earlier studies also found benefits for symptoms of schizophrenia with added L-theanine, with some disease symptoms showing modest to even moderate improvements (Miodownik 2011, Ritsner 2011).

L-Theanine, Parkinson’s and Alzheimer’s Disease  

A Cup of Tea

Neurodegenerative diseases associated with aging, including Parkinson’s and Alzheimer’s disease, currently have no standard treatments that slow their progression. These conditions are generally seen as a death sentence as the symptoms inexorably worsen over time. Due to the number of individuals suffering from these conditions, we desperately need new approaches to treatment. Research into L-theanine for neurodegenerative diseases appears to hold some promise. 

Parkinson’s disease is a movement disorder. The condition is characterized by an increasing difficulty in engaging muscular activity. Several environmental toxicants are known to damage the part of the brain responsible for the development of Parkinson’s disease. In a cell culture model, L-theanine was able to prevent damage and death to human cells upon exposure to toxicants implicated in the development of Parkinson’s disease (Cho 2008). 

In a rat model of Parkinson’s disease, L-theanine showed improvements in behavioral deficits, inflammation, neurotransmitter levels and cellular energy production (Raj 2021). Studies exploring tea consumption and Parkinson’s disease suggest that drinking 3 cups or more a day reduces the risk of Parkinson’s disease by 59% (Hu 2007). 

Similar to Parkinson’s disease, tea consumption has also been associated with a reduced risk of cognitive decline and dementia (Kakutani 2019). As mentioned previously, a few studies in humans have also found improved cognitive performance with L-theanine supplementation. A combination of green tea extract and L-theanine was found to improve memory and attention in older patients with mild cognitive decline. There was also evidence for increased alertness with supplementation (Park 2011). Similar to Parkinson’s, animal models of dementia and Alzheimer’s disease also appear to show benefits with L-theanine administration (Park 2018, Zhu 2018).  


L-theanine, a compound found in green tea, has been shown to have potential for supporting mental health. In addition, it also appears to have some promise for helping to prevent neurodegenerative diseases. With more research, we can hopefully better understand the effects of L-theanine and its benefits for brain health.  

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