Owari Satsuma mandarins, grown in Placer County from the suburbs of Sacramento to Lake Tahoe and the Nevada border, had up to six times as much synephrine as the same quantity of orange juice, the only citrus previously tested, a U.S. Department of Agriculture study said.

Ten ounces of mandarin juice contain as much synephrine as one over-the-counter decongestant pill, the study found.

"I always believed that Placer County mandarins had lots of synephrine," agriculture advocate Joanne Neft told the Sacramento Bee. "Every time I ate them, I felt so much better and my sniffles went away."

Whether Placer County mandarins have more synephrine than other varieties was not studied, the newspaper said.

The county's mandarin crop was about 625 tons in 2007 and had a value of $1.2 million, county agriculture marketing Director Nancyjo Riekse said. Mandarin production is expected to drop 40 percent this year due to weather, she said.