Think you've never touched cocaine in your life? Think again, says a new study, which found traces of the drug on more than 85 per cent of Canadian paper currency.

Researchers from the University of Massachusetts at Dartmouth conducted chemical tests on banknotes from 30 cities in five countries: Canada, the United States, Brazil, China and Japan.

They found the highest levels of cocaine on U.S. and Canadian currency, which had an average contamination rate of between 85 and 90 per cent.

China and Japan had the lowest contamination rates, between 12 and 20 per cent. Brazil was still high at 80 per cent of notes contaminated with coke.

The researchers presented their findings Sunday at a meeting of the American Chemical Society in Washington.

The findings suggest cocaine abuse is a more widespread problem than the average person realizes, and may be on the rise in some regions, lead study author Yuegang Zuo said in a news release.

According to Zuo, the percentage of contaminated U.S. currency rose nearly 20 per cent compared to a similar study conducted two years ago.

"I'm not sure why we've seen this apparent increase, but it could be related to the economic downturn, with stressed people turning to cocaine," Zuo said.

The research may offer some help to law enforcement and outreach agencies that want to study patterns of drug use in a given community, Zuo said.

Researchers are not at all surprised to find traces of cocaine on banknotes, which can become contaminated during drug deals or when a user snorts cocaine through a rolled-up bill.

Bills can also become contaminated when they pass through currency-counting machines at banks.

For their research, Zuo and his colleagues analyzed 234 U.S. banknotes and found that up to 90 per cent contained traces of cocaine.

Amounts ranged from .006 micrograms (which is several thousands of times smaller than a grain of sand) to more than 1,240 micrograms of cocaine (about 50 grains of sand).

But the highest levels were found on Canadian notes, with amounts ranging from 2.4 micrograms to more than 2,530 micrograms.

While the number of contaminated notes is high, the amount of cocaine is actually so small that average folks need not worry about potential health, or legal, problems.

"For the most part, you can't get high by sniffing a regular banknote, unless it was used directly in drug uptake or during a drug exchange," Zuo said. "It also won't affect your health and is unlikely interfere with blood and urine tests used for drug detection."