Los Angeles ? 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.

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

These new “relaxation” drinks have become popular fodder for food bloggers, with some calling Mary Jane’s “weed in a bottle.”

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 effects 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 restrictions for consumers.