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Side Effects of Suntheanine L-Theanine

By Rae Uddin ; Updated August 14, 2017

Suntheanine is the brand name of the generic natural supplement L-theanine. L-theanine is an amino acid derived from green tea leaves. This amino acid may help promote relaxation and is believed to help limit cancer cell growth by enhancing the effect of certain chemotherapeutic drugs, according to Memorial Sloan-Kettering Cancer Center. Few side effects are associated with tea extracts, such as L-theanine; however, you may experience side effects after consuming large amounts of green tea.

Upset Stomach

Stomach discomfort may occur as a side effect of tea extracts or excessive green tea consumption. As part of this stomach discomfort you may feel nauseated and experience a diminished appetite. Digestive irritation from consuming this tea extract is typically temporary and subsides quickly. Seek care from your physician if you experience persistent or severe stomach-related side effects.


You may experience headache pain after consuming tea extracts such as Suntheanine, warns Sensations of pain may develop across any region of your head and may range from mild to severe. If headache pain does not subside on its own, consider taking an over-the-counter pain medication to alleviate your discomfort.


Episodes of dizziness may develop as a side effect of this green tea extract, causing you to feel unstable or unsteady when you stand up or attempt to walk around. If you experience dizziness, remain seated until this sensation passes.

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