Lois Jordan runs a drug counseling center in Dallas that offers rehabilitation programs for teens, and she aided several families that were caught up in the Plano heroin use in the late 1990s.

She said cheese sounds a lot like "a poor man's speedball," a mixture of cocaine and heroin. The cheap, easily obtained Tylenol PM can contain stimulants and could provide the "rush" associated with cocaine in a speedball, she said.

"It's a unique combination that could give a rush of an amphetamine combined with a floaty high of an opiate." She said the cheap cost of cheese -- it's sold in small packages for between $2 and $10 -- could entice young users.

"The marketing that these drug dealers put together is just phenomenal," she said. "They really know how to tantalize kids and [exploit] their risk factors."

Drugs that are cheap and accessible, she said, "will increase user experimentation," adding that kids who start using drugs at a young age are at greater risk of addiction.

While the mixture of heroin and Tylenol PM appears to be new, the moniker "cheese" is not. Drug dealers and users have long used the term for heroin and other drugs. For example, "macaroni and cheese" is slang for a $10 bag of cocaine and a $5 bag of marijuana.

[Dallas police narcotics Deputy Chief Julian] Bernal said the Dallas Police Department has known about the new drug since around August.

"We didn't want to glamorize this," he said. "We initially wanted to keep this quiet, thinking it would go away. That didn't happen."

Authorities haven't said how potent the heroin is in the cheese they've found. The purity of different forms of heroin varies. Black tar heroin is about 30 to 34 percent pure. A more pure form of heroin that is commonly called "white China" is 80 percent pure or higher.

Police said cheese, even though it only has between 2 and 8 percent heroin, is still highly dangerous.