Larry, who asked that his last name not be used because of his habit, recited his rules after hearing that a mixture of heroin and a powerful painkiller has been killing users who believe they are taking heroin alone.

Officials from Philadelphia to Chicago have reported deaths from the drug, called fentanyl and considered 80 times more powerful than morphine. In the Detroit area — the apparent hub of the problem with more than 100 confirmed cases since last fall and as many as 41 possible deaths in the past eight days — officials from the national Centers for Disease Control and Prevention are investigating and community organizations are scrambling to get the word out to users.

The CDC says it has no national statistics on fentanyl deaths. But individual reports from a scattering of states indicate the drug mixture is widespread.

Philadelphia has had 20 confirmed deaths from heroin mixed with fentanyl since April 17, and test results are pending in eight suspected cases, the city health department said.

In New Jersey, where officials first raised the alarm about the drug in April, there have been about 10 confirmed fentanyl deaths and 10 to 20 suspected cases since last month, according to the state’s poison control center.

In Chicago, 30 people died from fentanyl or fentanyl-laced heroin from September 2005 to March 2006, said Christopher Hoyt, a spokesman for the U.S. Drug Enforcement Administration in that city. In addition, 23 suspected cases were reported in April and May.

"This is a huge, huge problem," said Stephen Marcus, medical director of the New Jersey Poison Control Center.

In Wayne County, which includes Detroit, Medical Examiner Carl J. Schmidt said he began noticing a rise in fentanyl-related deaths in September. In total, medical examiners found 63 people who died in Wayne County with fentanyl in their blood last year. From the beginning of 2006 to mid-April, there were 70 such cases.

County officials did not begin treating fentanyl as a crisis until last week, when the number of overdoses began to soar.

"Sometimes divining what the role of fentanyl is in an individual’s death is more an art than a science," Schmidt said, noting that drug users often have multiple substances in their blood.

Still, it was clear something was amiss when 12 people died of overdoses May 18-19, Schmidt said. In total, there have been 41 drug-related deaths since May 18, said Teresa Blossom, a spokeswoman for the Detroit-Wayne County Community Mental Health Agency. The county of 2 million typically sees two to three drug deaths a day.

The drug kills by inhibiting respiration, Schmidt said. "It literally suppresses your natural impulse to breathe," he said.

Before the recent surge, Wayne County saw 20 to 30 fentanyl deaths a year, Schmidt said. Those cases tended to be severely ill people with legitimate prescriptions who committed suicide or people who had stolen the drug, he said.

The fentanyl behind the current problem appears to be manufactured illegally and mixed with heroin long before it gets to the user, Schmidt said.

In one case, three people found dead in a car last month took fentanyl not with heroin but with cocaine. Schmidt said he fears that could indicate a new trend.

Organizations that run needle exchanges and other health programs for drug users are trying to spread the word. Officials emphasize there is help for people who have overdosed if they get to an emergency room immediately.

But to some drug users, the warnings are an advertisement.

"When they hear about people OD’ing somewhere, they want to go there" to get the more potent drugs, said Larry, the Detroit heroin user.

Like Larry, 37-year-old Latonja said she would do her best to stay away from the tainted heroin by sticking to dealers she knows. However, she acknowledged it may be difficult, because users can never know for sure what they’re buying.

"We’re not analyzers when we’re trying to shoot our dope," said Latonja, of Detroit, who also asked that her last name not be used. "We’re like, ‘OK, it’s time to get happy.’"