The St. Louis area has been flooded with a cheap new form of potent heroin, leading to a wave of overdoses, addiction and crime, The New York Times reports.

Mexican drug traffickers have been bringing this new form of heroin into the area, reducing prices and increasing the drug’s strength to attract people from the suburbs, the article notes.

Chicago, Baltimore, Milwaukee and Philadelphia have also seen increases in homicides partly due to trafficking of cheap heroin by Mexican cartels, who work with local gangs.

“The gangs have to have a lot of customers because the heroin is so cheap,” said Gary Tuggle, the Drug Enforcement Administration’s (DEA) chief in Philadelphia. “What we are seeing is these crews becoming more violent as they look to expand their turf.”

Cartels instruct gangs, usually through a local middleman, to sell heroin for as little as $5 per button—about a tenth of a gram, which is often enough to last a new user the entire day. DEA agents say sometimes gangs distribute free samples.

The drug’s purity level has greatly increased in recent years, according to federal officials. Purity levels have grown from 5 percent to 50 percent in St. Louis, while in Philadelphia they have reached as high as 90 percent.

Police data indicates while most heroin consumers and overdose victims in St. Louis are young whites in their 20s from suburbs and rural areas, almost all of the shooting victims and suspects have been African-American men and boys.

“What I’m seeing at street level are violent disputes about money owed around heroin debts, with sometimes the dispute being about money, and sometimes about drugs,” said St. Louis Police Chief D. Samuel Dotson III.