What are Theanine Side Effects?

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  • Written By: N. Madison
  • Edited By: Jenn Walker
  • Last Modified Date: 15 February 2020
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Theanine is an amino acid often found in tea. Studies have shown it may help to relieve mental or physical stress and may even improve cognition, among other things. While some types of supplements have long lists of side effects associated with them, theanine isn’t one of them. A person can usually take theanine without fear of side effects. This doesn’t mean theanine side effects are impossible. It just means there is no scientific evidence that they occur. Since each person may react to supplements differently, however, it’s wise to be alert for signs of adverse effects while taking it and report them to a medical doctor.

Theanine, which is often referred to as L-theanine, is a supplement used to support overall good health and prevent or help treat a range of medical conditions. Theanine is an amino acid that is found in green tea. It is said to be helpful for reducing stress and lowering anxiety levels. While it is useful as a calming agent, it doesn’t normally make people feel drowsy as other relaxing substances can.

Besides its calming effects, theanine is said to facilitate the production of similar calming substances in the body, such as serotonin. It may also be helpful for the treatment and prevention of such things as high blood pressure, premenstrual syndrome, and cancer. This substance may even help to boost the immune system and improve mental performance and concentration.


Though theanine has been in use for many years, there are no known theanine side effects. This may cause people to believe that it is a 100-percent safe supplement, but that is a misconception. The lack of reported theanine side effects simply means adverse effects haven’t been demonstrated in clinical studies or reported by health care providers. This doesn’t mean there are no possible theanine side effects. Additionally, it is possible that continued studies of theanine may one day show evidence of adverse effects.

Interestingly, at least one study of rats given theanine did produce significant instances of kidney tumors. Researchers believe, however, that the tumors were caused by factors other than the theanine exposure. Studies of rats exposed to theanine haven’t produced any other significant side effects.

Pregnant women and nursing mothers should consult their doctors before supplementing with theanine. The substance is usually considered safe, but its effects in pregnancy and during breastfeeding haven’t been studied extensively. Additionally, the kidneys and the liver are important in the processing of excess amounts of theanine and other supplements. As such, a person with liver or kidney disease should seek his doctor's advice before using theanine as a supplement.


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