In Los Angeles, where medical marijuana dispensaries outnumber Starbucks and McDonald’s restaurants combined, a mood-altering beverage with a Cannabis-oriented marketing campaign is gaining traction.

Southern California has become the best-selling market for Mary Jane’s Relaxing Soda, a sugary drink laced with kava, a South Pacific root purported to have sedative properties.

Matt Moody, a Denver nutritional supplement developer who created the beverage, said the name is an unabashed reference to weed, though the relaxant compounds in kava are chemically unrelated to those in marijuana.

Along with new drinks like Slow Cow and Ex Chill, Mary Jane’s is part of a new group of so-called slow-down or anti-energy drinks, and are expected to be one of the top food trends of 2010, according to advertising agency J. Walter Thompson.

They rely on folk medicine sedatives, including kava, chamomile and valerian, to provide an alternative from caffeine-laced and jitter-inducing energy drinks such as Red Bull.

The drinks purportedly promote calming and also take on the energy-drink category directly by claiming to also boost mental focus and concentration, said Ann Mack, director of trendspotting at the agency.

“It is a new category, kind of like energy drinks, but designed to relax people,” Travis Arnesen, spokesman for Ex Drinks of Henderson, Nev., said. “Just recently it has been picking up steam.”

Its Ex Chill drink comes in an 8.4 ounce can and sells for $2 in Albertsons and 7-Elevens. Slow Cow, made by Boisson Slow Cow Inc. of Quebec, plans to start distribution in the U.S. next year.

Kava has long been “a popular recreational drug through much of the Pacific, especially Vanuatu, Fiji, Samoa and Tonga,” said Lamont Lindstrom, a University of Tulsa anthropologist who has studied the use of the plant in Pacific Islander culture.

The calming effect that people enjoy from kava is probably real, said Michael Pollastri, a pharmaceuticals chemist at Boston University.

“If there were not therapeutic affects it would not be a thousand-year-old folk medicine,” Pollastri said.

Kava warrants a closer look by drug chemists to figure out how it works as a relaxant and what it else it might be useful for, but that work is just beginning, he said.

There are no age limits or other restrictions for consumers. Medical experts, however, caution that drinks containing kava and other supplements could have a downside, depending on the chemical compounds used as ingredients and how the plants are processed.

The Food and Drug Administration has issued a warning that people with “liver disease or liver problems, or persons who are taking drug products that can affect the liver, should consult a physician before using kava-containing supplements.” But the agency has not restricted sales of kava-based products.

The kava root’s “awful taste” was one reason why it has not gained the same acceptance of other folk-based nutritional supplements, Moody said. But blending it into a drink that contains cane sugar solved that. Another beverage company makes it on contract for his Denver-based Mary Jane’s Soda Inc. Moody said his beverage also sells in scattered bars and cafes, and online through the Mary Jane’s Soda Inc. Web site.

Nathan Scholl, a waiter at a Santa Monica restaurant, said he’s “hooked” on the cola-colored liquid that comes packed in a clear 12-ounce bottle with a blue label.

While the drink doesn’t make him high, Scholl said he finds “the whole Mary Jane thing funny.”

“I drink it after a long day. It takes five or 10 minutes to sink in and then I feel relaxed and slightly euphoric,” Scholl said.