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Theanine: Uses and Risks

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Theanine is an amino acid, a building block for protein. It's naturally in tea leaves, especially green tea. Many people drink green tea because it helps them feel calm.

Why do people take theanine?

Theanine supplements may help people feel more relaxed and lower anxiety, some early studies have shown. Theanine supplements helped boys with ADHD sleep better in one small study. Another small study showed that when combined with caffeine, theanine may sharpen thinking.  More research is needed to see how theanine affects these conditions.

People who drink green tea -- which is high in theanine -- had a lower risk of stroke, one study found. We don't know if it was the theanine or another component of green tea that had the benefit.

Some animal and lab studies show that theanine could help with dementia, high blood pressure, and unhealthy cholesterol levels. Theanine could also boost the benefits -- and reduce side effects -- of some drugs for cancer treatment. But we don't yet know whether theanine supplements would have these benefits in people. We need more research to know for sure.

Standard doses of theanine have not been set for any condition. Ingredients in supplements may vary widely. This makes it very hard to set a standard dose.

Can you get theanine naturally from foods?

Theanine is found in tea, especially green tea. It is also found in mushrooms.

What are the risks?

Tell your doctor about any supplements you're taking, even if they're natural. That way, your doctor can check on any potential side effects or interactions with medications.

  • Side effects. Studies have not found side effects from using theanine supplements. Drinking lots of green tea can cause upset stomach and irritability from the caffeine. It's not clear if using theanine supplements in the long-term is safe.
  • Risks. We don't know if theanine is safe for children or for women who are pregnant or breastfeeding.
  • Interactions. If you take any medicines regularly, talk to your doctor before you start using theanine supplements. They could interact with stimulants, sedatives, and drugs for high blood pressure, cancer, and high cholesterol.

Supplements are not regulated by the FDA.

WebMD Medical Reference

Reviewed by Melinda Ratini, DO, MS on February 06, 2013

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