Theanine is an amino acid found in tea. It is also found in some mushrooms. Theanine comes in two forms - L-theanine and D-theanine. L-theanine is the form most commonly found in tea and supplements.

L-theanine is used to improve mental function. It is also used for anxiety, mental impairment, stress, and other conditions, but there is no good scientific evidence to support these uses.

How does it work ?

Theanine has a chemical structure very similar to glutamate, a naturally occurring amino acid in the body that helps transmit nerve impulses in the brain. Some of the effects of theanine appear to be similar to glutamate, and some effects seem to block glutamate.

Uses & Effectiveness ?

Possibly Effective for

  • Memory and thinking skills (cognitive function). Taking L-theanine might help healthy people stay focused on a task over long periods of time. It might also help people with lower thinking skills perform tasks that require them to find words in a specific category. But it doesn't seem to improve other measures of memory or thinking. It isn't clear if adding L-theanine to caffeine works better than using either of those ingredients alone.

Insufficient Evidence for

  • Anxiety. Early research shows that taking L-theanine daily for 4 weeks reduces stress-related anxiety. But it doesn't seem to help with other types of anxiety.
  • Ability to pay attention. Early research shows that taking L-theanine 200 mg before a test improves attention. But lower doses might not help.
  • Attention deficit-hyperactivity disorder (ADHD). Some early research shows that taking L-theanine might improve memory and thinking skills, but not attention or impulse control, in children with ADHD. Other early research shows that taking L-theanine increases restful sleep and decreases nightly activity during sleep in males ages 8-12 with ADHD.
  • Diarrhea caused by cancer drug treatment. Taking a product containing L-cysteine and L-theanine might reduce diarrhea and loss of appetite caused by some cancer drugs in people with colon cancer. But it doesn't seem to reduce these side effects of cancer drugs in people with stomach cancer. It also doesn't seem to reduce diarrhea caused by all cancer drugs.
  • Depression. Early research shows that taking theanine by mouth at bedtime for 8 weeks decreases symptoms and improves sleep in people with depression.
  • Schizophrenia. Some early research shows that taking L-theanine by mouth along with prescribed drugs improves some symptoms of schizophrenia. More research is needed to determine the effects, if any, of L-theanine on symptoms of schizophrenia.
  • Stress. Some early research shows that taking L-theanine 200 mg before an exam or school practicum experience reduces stress. But not all research agrees.
  • Alzheimer disease.
  • Cancer.
  • Decline in memory and thinking skills in older people that is more than what is normal for their age.
  • Flu (influenza).
  • High blood pressure.
  • Insomnia.
  • Other conditions.
More evidence is needed to rate the effectiveness of theanine for these uses.

Side Effects

When taken by mouth: L-theanine is POSSIBLY SAFE when taken by mouth, short-term. Doses of up to 900 mg of L-theanine daily have been safely used for 8 weeks. It is unknown if L-theanine is safe when used for longer periods of time. L-theanine may cause mild adverse effects, such as headache or sleepiness.

Special Precautions and Warnings

Pregnancy and breast-feeding: There isn't enough reliable information to know if theanine is safe to use when pregnant or breast-feeding. Stay on the safe side and avoid use.

Children: L-theanine is POSSIBLY SAFE for children when taken by mouth, short-term. Doses of 200 mg of L-theanine have been safely used twice daily for up to 6 weeks in males aged 8-12 years.

Low blood pressure: Theanine might lower blood pressure. In theory, theanine might increase the risk of blood pressure dropping too low in people prone to low blood pressure. If you have low blood pressure, discuss theanine with your healthcare provider before starting it.

Interactions ?

    Moderate Interaction

    Be cautious with this combination

  • Medications for high blood pressure (Antihypertensive drugs) interacts with THEANINE

    Theanine seems to decrease blood pressure. Taking theanine along with medications for high blood pressure might cause your blood pressure to go too low.

    Some medications for high blood pressure include captopril (Capoten), enalapril (Vasotec), losartan (Cozaar), valsartan (Diovan), diltiazem (Cardizem), Amlodipine (Norvasc), hydrochlorothiazide (HydroDiuril), furosemide (Lasix), and many others.

  • Stimulant drugs interacts with THEANINE

    Stimulant drugs speed up the nervous system. By speeding up the nervous system stimulant medications can make you feel jittery and speed up your heartbeat. Theanine might work to slow down the nervous system. Taking theanine along with stimulant medications might decrease the effectiveness of stimulant medications.

    Some stimulant drugs include diethylpropion (Tenuate), epinephrine, phentermine (Ionamin), pseudoephedrine (Sudafed), and many others.


The following doses have been studied in scientific research:


  • For memory and thinking skills (cognitive function): A single dose of 100 mg of L-theanine before a test has been used. L-theanine 200 mg daily for 4 weeks has been used. L-theanine has also been used in combination with caffeine. Combination doses have ranged from 30-100 mg of caffeine and 12-100 mg of L-theanine.
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CONDITIONS OF USE AND IMPORTANT INFORMATION: This information is meant to supplement, not replace advice from your doctor or healthcare provider and is not meant to cover all possible uses, precautions, interactions or adverse effects. This information may not fit your specific health circumstances. Never delay or disregard seeking professional medical advice from your doctor or other qualified health care provider because of something you have read on WebMD. You should always speak with your doctor or health care professional before you start, stop, or change any prescribed part of your health care plan or treatment and to determine what course of therapy is right for you.

This copyrighted material is provided by Natural Medicines Comprehensive Database Consumer Version. Information from this source is evidence-based and objective, and without commercial influence. For professional medical information on natural medicines, see Natural Medicines Comprehensive Database Professional Version. © Therapeutic Research Faculty 2018.