Q. I've heard that L-theanine (a compound in tea) can reduce stress. Is it safe as a supplement? How much should I take?

A. The amino acid L-theanine is found almost exclusively in the Camellia sinensis plant, whose leaves are used to brew tea—the second-most widely consumed beverage in the world, after water. L-theanine contributes to tea's unique taste and counteracts some of the stimulant effects of caffeine. A typical cup of tea contains between 20 and 60 mg of L-theanine. To get the greatest calming effect from L-theanine, without any of the stimulating effects of caffeine, you can drink decaffeinated tea or take L-theanine as a stand-alone supplement.

Taking L-theanine as a dietary supplement can promote a relaxed but alert state of mind. By altering levels of serotonin, dopamine, and other neurotransmitters in the body, it encourages relaxation without leading to drowsiness. In one study of university students, taking 200 mg of L-theanine eased anxiety and increased alpha brain wave activity (the type associated with relaxation) after 40 minutes. In laboratory and animal research, L-theanine has also been shown to lower blood pressure, improve learning ability, and combat cancer.

If you're feeling stressed, give L-theanine a try. It's very safe, with no reported side effects or adverse reactions. Take 200 mg, once or twice a day, for an improved sense of well-being.

This Q&A was written by Victoria Dolby Toews, MPH, author of User's Guide to Sexual Satisfaction (Basic Health, 2003).