If you live in the United States or Canada, chances are you have cocaine in your wallet.

Nearly nine out of ten bills circulating in the U.S. and its northern neighbor are tainted with cocaine, according to what's being called the most definitive research to date on the subject.

What's more, researchers were surprised to find hints that more Americans are using the illegal drug, said study leader Yuegang Zuo of the University of Massachusetts in Dartmouth.

In a similar study by the same team in 2007, 67 percent of U.S. bills were found to be tainted with cocaine. The new study puts the percentage at 85 to 95—a jump of roughly 20 percent, Zuo said.

The drug gets on paper money during drug transactions and when people roll bills to snort cocaine powder, Zuo said.

Stress spurred by the worldwide financial crisis may be driving people to abuse cocaine, one of the most common illegal drugs in the world, Zuo said in a phone interview.

The new findings could "help raise public awareness about cocaine use and lead to greater emphasis on curbing its abuse," Zuo said in a follow-up email.

Cocaine Country

Part of the reason the new study is so complete, Zuo said, is because the team used new equipment, a gas chromatograph-mass spectrometer, which doesn't ruin the money—allowing the scientists to test more bills without breaking the bank.

The team collected banknotes from Brazil, Canada, the U.S., China, and Japan.

With 5.8 million people having used the drug at least once in 2007, the U.S. is the world's biggest cocaine market, according to the 2009 UN World Drug Report.

Perhaps not surprisingly, then, the U.S.—along with Canada—had the highest percentage of cocaine-permeated bills in the study.

Of the 234 U.S. bills collected in 17 large and small cities, nearly 90 percent had traces of cocaine, especially in larger cities such as Baltimore, Boston, and Detroit. Ninety-five percent of the dollars found in

In keeping with their reputations for having relatively low rates of cocaine use, China and Japan yielded bills with relatively low levels of cocaine contamination.

Asian drug-taking practices could conceivably be partly responsible for the lower percentages of cocaine-tainted bills. Zuo doesn't know, for example, whether Asian cocaine users inhale through rolled bills as many Western users do.

"It is for sure that drug abuse in different countries and regions has different use patterns which may affect cocaine contamination on money," he said via email.

Regardless of where you live, though, there's little chance of getting buzzed off your bills, Zuo said. Even in the U.S. and Canada, the concentrations are simply too small.