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

Theanine is similar to glutamate, a naturally occurring amino acid. Glutamate helps transmit nerve impulses in the brain. Theanine sometimes acts like glutamate in the body. But other times it seems to block the effects of glutamate. Theanine might also affect the brain chemicals GABA, dopamine, and serotonin.

People use L-theanine 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.

Don't confuse theanine with another amino acid called threonine. These are not the same.
When taken by mouth: L-theanine is possibly safe when used short-term. Doses of up to 900 mg daily have been safely used for 8 weeks. It isn't clear if L-theanine is safe to use for longer periods of time. It might cause mild side effects, such as headache or sleepiness.

Special Precautions & 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 when taken by mouth, short-term. Doses of 400 mg daily have been safely used for up to 6 weeks in males aged 8-12 years.


NatMed Pro rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.
Likely effective Effectiveness definitions
Possibly effective Effectiveness definitions
  • Memory and thinking skills (cognitive function). Taking L-theanine by mouth might help healthy people stay focused. It isn't clear if adding L-theanine to caffeine works better than using either of those ingredients alone.
There is interest in using L-theanine for a number of other purposes, but there isn't enough reliable information to say whether it might be helpful.
Likely ineffective Effectiveness definitions
Possibly ineffective Effectiveness definitions
Insufficient evidence Effectiveness definitions

Dosing & administration

L-theanine is naturally found in tea and some mushrooms. As medicine, L-theanine has most often been used by adults in doses of 200-400 mg by mouth daily for 4-8 weeks. Speak with a healthcare provider to find out what dose might be best for a specific condition.

Interactions with pharmaceuticals

Medications for high blood pressure (Antihypertensive drugs)

Interaction Rating=Moderate Be cautious with this combination.

Theanine might lower blood pressure. Taking theanine along with medications that lower blood pressure might cause blood pressure to go too low. Monitor your blood pressure closely.

Sedative medications (CNS depressants)

Interaction Rating=Minor Be watchful with this combination.

Some medications, called sedatives, can cause sleepiness and slowed breathing. There is some concern that theanine might also cause sleepiness and slowed breathing. But most research hasn't shown this effect. For now, use theanine with caution if you are taking sedative medications.

Interactions with herbs & supplements

Herbs and supplements that might lower blood pressure: Theanine might lower blood pressure. Taking it with other supplements that have the same effect might cause blood pressure to drop too much. Examples of supplements with this effect include andrographis, casein peptides, L-arginine, niacin, and stinging nettle.

Interactions with foods

There are no known interactions with foods.
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This monograph was last reviewed on 30/04/2023 10:00:00 and last updated on 29/06/2022 07:53:26. Monographs are reviewed and/or updated multiple times per month and at least once per year.
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