Drug cartels are selling lethal doses of fentanyl disguised as street heroin and counterfeit OxyContin pills, two U.S. government agencies are warning. The Drug Enforcement Administration and the Department of Justice are cautioning people who buy illegal drugs and painkillers on the street or in Tijuana, Mexico, that cartels are using fentanyl because they can produce it more cheaply. Just a few grains of fentanyl can be lethal, the agencies said. In September, authorities confiscated more than 70 pounds of fentanyl and 6,000 counterfeit pills, NBC 7 reports. “It’s extremely profitable for the cartels. They aren’t having to wait for harvest. They aren’t having to harvest the poppy plants. They’re not having to manufacture that paste into heroin. They are literally just getting a chemical from China,” DEA spokeswoman Amy Roderick told NBC 7 .