L-theanine is an amino acid found most commonly in tea leaves and in small amounts in Bay Bolete mushrooms. It can be found in both green and black tea. It’s also available in pill or tablet form at many drugstores.

Research indicates that L-theanine promotes relaxation without drowsiness. Many people take L-theanine to help ease stress and unwind. Small studies and tests on animals have shown that L-theanine may offer a range of benefits. Experts consider it to be generally safe, but there is currently a lack of high-quality research in humans to confirm its benefits.

What are the benefits of L-theanine?

The following sections discuss the existing evidence for the possible benefits of L-theanine.

1. Better mental focus

Many people drink black or green tea while at work, believing that it boosts their mental focus. A 2012 study supports this idea.

The researchers found that people who took 100 milligrams (mg) of L-theanine made fewer errors in an attention task than those in the placebo group. Drinking 50 mg of caffeine or combining the L-theanine and caffeine also improved people's focus.More research is necessary to determine how L-theanine might affect a person's attention and focus.

2. Improved sleep

L-theanine may help people sleep more easily.Several studies have suggested that L-theanine could help people relax before bedtime, get to sleep more easily, and sleep more deeply.These benefits may result from the specific effects that the amino acid has on brain chemicals that play a role in sleep.

A 2018 study found that people reported having greater sleep satisfaction after taking 450–900 mg of L-theanine daily for 8 weeks. The study participants had generalized anxiety disorder and were taking antidepressants.

3. Relaxation

People often drink a cup of tea or another hot beverage to help them relax. Research suggests that the L-theanine in green or black tea may contribute to this feeling of relaxation by reducing a person's resting heart rate.

4. Increased cognitive performance

In 2016, researchers reviewed the existing research on the benefits of L-theanine and concluded that this compound could benefit a person's mental and physical health. They noted that it seems to have neuroprotective effects, which improve brain function.

On its own, L-theanine may improve a person's attention and reaction times. In combination with caffeine, it may lead to improvements in their number skills and alertness. Caffeine is a stimulant, so it can help people stay alert and focused.

However, not all research has found that L-theanine can improve people's cognitive abilities. There is a need for more high-quality research to clarify the effects of this compound on people's mental functions.

5. Weight loss

As part of a calorie-controlled diet, replacing a snack with green tea or another low-calorie hot beverage could aid weight loss.The L-theanine in green tea can create a savory taste, also known as umami flavor. Research suggests that umami flavors may reduce appetite, which often helps with weight loss.

6. Boosting the immune system

L-theanine may support the body in fighting off illness. Several studies have suggested that taking L-theanine could boost a person's immune system, making them less likely to get common colds or the flu.Its potential anti-inflammatory effects could also help fight illness.

7. Reducing blood pressure

Research has linked high blood pressure with a higher risk of several health problems, including heart attack and stroke.L-theanine may help reduce stress, and a reduction in stress and increased relaxation can lower the heart rate. In turn, this may help lower blood pressure.

8. Supporting certain cancer drugs

Some research on animals suggests that L-theanine may increase the effectiveness of a chemotherapy drug called doxorubicin. It is possible that it makes doxorubicin more effective by increasing the amount of the drug in cancer cells. However, scientists need to do more research to understand the specific interactions between these chemicals.