This information describes the common uses of L-Theanine, how it works, and its possible side effects.

Common Name

Theanine, Gamma-glutamylethylamide, N-ethylglutamic acid

How It Works

L-theanine has not been shown to treat or prevent cancer.

L-theanine is an amino acid found in green tea. An epidemiological study showed that the incidence of stroke was reduced in individuals who consumed green tea. However, it is unclear whether L-theanine contributed to this benefit.

Laboratory and animal studies showed that L-theanine increases efficiency of chemotherapy drugs and also reduces their side effects. However, patients undergoing chemotherapy should discuss the use of L-theanine with their physicians because these effects are not based on clinical trials, and another component found in green tea called epigallocatechin-3-gallate (EGCG) reduces activity of the chemotherapy drug bortezomib.

Purported Uses

  • Relaxant
    In patients with schizophrenia, two studies have shown that L-theanine alleviates anxiety, and improves sleep and other related symptoms when combined with antipsychotic treatment.
  • Cancer prevention
    There is no scientific evidence to substantiate this use.
  • Cancer treatment
    Laboratory and animal studies indicate that L-theanine has antitumor properties, but human data are lacking.
  • Stroke
    Results from a study done in Japan suggest that green tea consumption decreased the risk of stroke in individuals. However, it is unclear if L-theanine contributed to this benefit.
  • Attention deficit hyperactivity disorder (ADHD)
    A small study suggests L-theanine can improve sleep quality in boys with ADHD.

Patient Warnings

Although there are no reported side effects from taking L-theanine, consumption of large amounts of green tea can cause nausea, irritability, and GI upset because of its caffeine content.

Side Effects

Please see monograph on green tea.