Police in Edmonton, Canada are reporting the seizure of a large amount of a synthetic drug, W-18, which they say is 100 times more powerful than fentanyl, according to Fox News.

W-18 is 10,000 times more powerful than morphine, and produces a heroin-like high, the article notes. The Edmonton police seized 4 kilograms, enough to make hundreds of millions of pills, according to The Globe and Mail. The drug is likely being produced in China.

In March, the Sun Sentinel reported that a drug dealer in Florida who was convicted of importing fentanyl also had 2.5 pounds of W-18.

According to CBC News, W-18 and a number of similar compounds were invented by researchers at the University of Alberta in the 1980s as potential pain relievers. The drugs were patented in 1984, but had no known use outside of scientific research.

Laura Calhoun, a medical director at Alberta Health Service, said because W-18 cannot be detected in urine or blood drug tests, there is no way to track how many drug overdoses may be due to the drug. “Our message to the public is this: No matter what drug you use, W-18 or fentanyl may be hiding in it and it may kill you,” she said.