Not long ago, a friend started telling about L-Theanine [1], a natural supplement that she'd started taking to help her sleep.

It helped her get a great night's rest, she told me, but it also generally made her feel more relaxed. Taking it made her feel calm, cool, and collected throughout the day.

I'd never heard anything about L-Theanine, but after hearing about her experience, I started poking around on Google to learn more about it.

What I learned was that L-Theanine is an amino acid that's found only in tea [2]. In fact, it's the ingredient that gives green tea such a distinct flavor.

It's believed to reduce stress and increase relaxation without causing drowsiness. It's also been shown to increase alpha waves in the brain, which measure relaxation.

There's evidence [3] to show that it increases the body's ability to fight infection and boost immunity. Limited research also shows that it could help the body fight tumors and lower blood pressure.

It seems very safe [4]. It's been used extensively in Japan since 1964, and years of research have shown no negative side effects.

Now, I've never been too big on supplements, in general. I take a multivitamin, and occasionally some Omega-3 fatty acid [5] capsules.

And many, many years ago, I tried some popular supplments that promised the same benefits, including St. John's Wort and SAM-e. But they didn't seem to do much for me personally, and I quit taking each one after a couple of weeks.

A few days ago, I decided to give L-Theanine a try. I bought a bottle of capsules at a nearby natural foods store. Then, as directed, I took one and waited to see how I felt. They're supposed to take effect within an hour or so.

My verdict: I'm pretty sure that it worked.

I felt more relaxed, but not in a strange way. If anything, I feel like I went to a yoga [5] class earlier in the day. I didn't feel blissed out, but I liked feeling some of that post-yoga sense of calm and balance for the rest of the day.