Loaded with caffeine and taurine to stimulate the central nervous system, energy drinks have become the go-to solution when you need a quick, energizing pick-me-up.

But sometimes energy isn't what you need. Concentration and attention can start to fade in the face of those midafternoon doldrums and a host of distractions. Something to perk up the mind and enhance focus would do the trick.

Some beverage manufacturers say they have just the solution. They're touting a new kind of drink that emphasizes focus over ferocity. The key substance is the amino acid L-theanine, which preliminary research suggests might calm the brain to enhance concentration and mental stamina.

Certain formulations of SoBe Lifewater and Vitamin Water contain L-theanine, as does a new beverage called ViB. And Gatorade recently introduced a drink with the amino acid as well. That product -- Tiger -- was named for and marketed by golfer Tiger Woods, the king of concentration in the sports world.

''Focus and concentration is the next generation of the energy drink,'' says Scott Smith, vice president of Taiyo International, a major producer of L-theanine in a patented tea extract called Suntheanine. ``This will put you in an alert state -- in a zone -- but it's not going to keep you up at night.''

L-theanine is not a new discovery. The substance comes from the Camellia sinensis plant species, otherwise known as tea.

Despite its caffeine content, tea is cherished for its soothing effects.

''It's one of the reasons people drink tea,'' says Dr. Jack F. Bukowski, a scientist with the Nutritional Science Research Institute, an industry-based nonprofit organization that studies nutritional supplements. ``The combination of the caffeine and the L-theanine gives people the same amount of energy as caffeine alone but less of a jittery-ness.''

That may be true for a cup of tea. But much less is known about the benefits of L-theanine when it's extracted from tea and packed into pills or blended into beverages at quadruple the dose.

''We've gotten that wrong before,'' says Lenore Arab, a professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles. ``We've learned so often that we make a mistake if we pull a substance out and take it in a supplement. But L-theanine is an interesting substance.''

The studies done on L-theanine thus far have been small, funded largely by companies with an interest in the product. That's not surprising. Early research on a potential supplement is often done by companies that believe there's a profit to be made. What remains to be seen is whether large-scale studies will back up early findings.

What intrigues researchers thus far is evidence that L-theanine is readily absorbed in large quantities, crosses the blood-brain barrier and gets into the brain fast.

Several studies suggest that the substance stimulates alpha waves in the brain, which are associated with alertness. The brain generates a range of electrical activity that reflects various mental states, such as sleep, daydreaming, agitation or concentration. The alpha waves represent the alert state.

• In one study, the alpha rhythms of 13 people were monitored with electroencephalography, more commonly called EEG, which records electrical activity in the brain. Participants performed a demanding visual-spatial attention task after being given either 250 milligrams of L-theanine or a placebo.

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