L-Theanine is an amino acid most commonly found in green tea. It has a similar chemical structure to glutamate, the most abundant neurotransmitter in the brain, which plays a part in normal brain function, including learning, mood stabilization, and memory.

Studies show that L-Theanine may have similar effects on the brain and many additional benefits.

How It Works

Not only does L-Theanine elevate calming brain chemicals, like serotonin and dopamine, but it also reduces the chemicals that are likely to cause anxiety and stress.

The amino acid also triggers alpha waves in the brain, which are linked with relaxation. These three effects can have a significant impact on how a person copes with anxiety and stress.

digital illustration of neurons on brain background


Cognitive Function

L-Theanine may positively affect cognitive function in healthy adults. One study looked at the effects of four weeks of L-Theanine supplementation on brain function by scoring participants across a variety of categories.

Scores for stress-related symptoms, like anxiety and depression, decreased, while those for cognitive function, like fluency and problem-solving, increased. Study participants with low performance in verbal fluency at baseline saw notable improvement after using L-Theanine.

intelligent woman problem-solving at work



Another study looked at how L-Theanine affected stress levels, asking participants to complete tasks at baseline and then again one hour and three hours after consuming a drink with L-Theanine. Results show that not only were stress levels significantly lower at the one-hour mark, but cortisol responses were also significantly reduced at three hours. Cortisol is known as the "stress hormone" and helps control blood sugar and blood pressure and affects multiple body systems.

hand turning cubes to spell Less Stress


Opioid Dependence

Between 21 and 29 percent of people prescribed opioids for chronic pain use them other than as intended, and between 8 and 12 percent develop an addiction.

One reason people have a hard time coming off of opioids is because of withdrawal symptoms, but one study shows that L-Theanine may help. When morphine-addicted monkeys in this study received L-Theanine, signs of withdrawal — like pacing, retching, and fighting — decreased.

doctor holding a handful of prescription pills



L-Theanine may also have sleep benefits. Many medications taken to help with sleep problems have unexpected side effects and can either lead to dependence or stop working when used long-term.

One study showed that when L-Theanine was taken with GABA, another amino acid available as a supplement, both the quality and duration of sleep improved. Interestingly, the combination of L-Theanine and GABA was more effective than either of these supplements alone.

older man sleeping in his bed


Blood Pressure

One study shows that L-Theanine may also help manage blood pressure. This study looked at how L-Theanine and caffeine affect the ability to complete tasks when under stress. The results show that L-Theanine inhibited blood pressure increases in study participants whose blood pressure increased more than an average amount after taking the placebo.

These results indicate that not only does L-Theanine reduce the feeling of anxiety, but it also moderates blood pressure in those prone to having a high-stress reaction.

hand holding weight while blood pressure test; healthy concept



L-Theanine is most commonly found in green tea, and many studies have looked at the effects of green tea on cancer. Various studies show tea drinking is associated with a lower risk of lung cancer, breast cancer, esophageal cancer, colon cancer, and liver cancer. Another study showed that L-Theanine can enhance the effects of several chemotherapy agents. More data is needed, but the research suggests that L-Theanine may be effective at preventing or treating cancer.

smiling mother with cancer hugging daughter


Pros of L-Theanine

In addition to all of its reported health benefits, L-Theanine is generally safe to take, though dosing has not been determined. Studies have demonstrated that it is well-tolerated, and there are no serious side effects. It is not habit-forming, and there are no signs of dependence when used for longer periods of time.

woman about to drink green tea


Cons of L-Theanine

The biggest downside to L-Theanine is that it may interact with some medications and supplements. Some people choose to take L-Theanine supplements rather than drinking green tea. Supplements are not regulated by the FDA, so consumers cannot be sure of the efficacy, safety, or dosing of the one they choose.

supplements on a table


Who Should Avoid L-Theanine

People who are pregnant, breastfeeding, or have an allergy or sensitivity to green tea should avoid taking L-Theanine. It can also interfere with the effects of caffeine or cause blood pressure to drop too much in people who are taking other medications to control it.

People taking medications or supplements to manage sleep disorders, anxiety disorders, or hypertension should talk to their doctors before taking L-Theanine.

smiling pregnant woman and her partner


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