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L-Theanine is an amino acid that is not commonly obtained through dietary sources. It is structurally similar to the neurotransmitters GABA and glutamate, and acts in a similar manner in the brain following oral ingestion.
L-Theanine has been found to act as a relaxing agent without causing sedation, as well as reducing stress and improving attention. These properties make it ideal for combining with stimulants as a way to attenuate some of their side effects. The combination of L-Theanine and Caffeine, for example, has been shown to be very effective at improving both general cognitive function and the ability to pay attention.
The typically recommended dosage of L-Theanine is 100 – 200 mg, although when combined with Caffeine a dosage of 200 mg is more common. There is evidence that exceeding a dosage of 200 mg has little additional benefit, as when more than 200 mg is taken the excess is used by the body as a raw material for protein production.
While the standard 200 mg dosage can be exceeded without much risk of adverse side effects, it is generally a waste of money and is not recommended.
L-Theanine is very well tolerated by the body and is not toxic. Adverse side effects are rare, but include headaches, dizziness, and mild gastrointestinal discomfort.
One other potential side effect of L-Theanine is a temporary reduction in blood pressure. While this is normally a beneficial side effect, caution should be used when combining L-Theanine with prescription medications that also reduce blood pressure.