L theanine is one of the non essential amino acids, which is having a very special role in the human body. The body makes L-theanine with the help of other essential amino acids. L theanine nourishes the brain and provides relief from stress. L- theanine can be extracted from the natural source other than the human body. The green tea plant has a great amount of theanine in it.  People often use green tea and black tea in their routine life. Increased amount of theanine in the human body does not cause any harm to the body. Theanine extracted from tea has many vital functions in the human body, such as sleep, immune system strength and controlling the blood pressure.

According to some medical specialists using theanine as a food supplement has no side effects. Individuals who are taking green tea (rich in theanine) never complained about any adverse effects on their health. Some people think that if a greater amount of theanine is present in the body, the individual may feel dizzy or in some cases nausea and headache are also seen. However, no experimental proof is available. A survey was carried out a few years ago by medical students, they found that people who are having greater amounts of theanine in their body were having fresh and glowing skin. Although the reason for this effect is unknown and requires further research. No harmful effects of theanine are seen untill now. Theanine may act as a mind relaxant and in a few cases it may prevent the individual from stroke and memory loss. Few researchers say that theanine helps in the release of dopamine. Dopamine is a hormone that produces a sense of well being; it is released during pleasurable activities such as sex or eating. Greater levels of theanine results in the increased amount of dopamine in the body. This increased amount of dopamine may sometimes cause nausea to the individual. Although, no scientific proof is available about this phenomena. Theanine as a food supplement acts as an immune booster and also prevents the body from bacterial infections. No side effects of the theanine are reported yet. People who use green tea claim that it is safe and can be taken several times in a day. Green tea contains a great amount of theanine in it, taking tea frequently in a day may lead to increased amounts of theanine in the body. Greater amount of theanine has no harmful effects to the human body. There might be some possible interactions when using L-theanine that can cause problems. Still there is no research indicating that theanine is problematic when used as a food supplement.

Although it is stated by some medical professionals that people who are taking sedatives in routine must not take theanine rich diets. The reason behind is that theanine is a mind relaxant and people who are taking sedatives may feel prolonged sedation. Again, there are  no studies that indicate potential side effects of theanine. It is not possible to find evidence that L- theanine has negative side effects; every person is different and their body may show a different response towards theanine. L- theanine is a naturally occurring substance, so it is considered to be safe for all the people. L-theanine is found to be having no side effect on pregnant women and children. The theanine extract from the green tea plant is considered safe for all the individuals.