Why do drug dealers overfose (but not enough to kiII) a user on purpose?

Heroin is stronger and cheaper than pharmaceutical opioids and is therefore attractive to users whose addictions began with prescription drugs.

And fentanyl, lethal as it is, is stronger and cheaper than heroin.

By adding fentanyl, dealers are able to augment a diluted supply of heroin or offer users a stronger kick.

“Obviously, there are no regulations, no quality controls,” said Robert Bell, assistant special agent in charge of Drug Enforcement Administration’s Milwaukee district office.

In other words, it's a guess how much fentanyl to add, Bell said.

"You don't have to be wrong by much to kill somebody," he said.

Fentanyl looks the same as heroin; users have no idea which they are using. And fentanyl available on the street is made in illegal labs — not pharmaceutical companies — so the quality or consistency varies.

Used correctly, fentanyl can work wonders, easing extreme pain in patients. Used incorrectly, an amount the size of three grains of sand can be deadly. The musician Prince died of a fentanyl overdose, and the drug is becoming so widespread that the Drug Enforcement Administration and the Centers for Disease Control and Prevention say it has reached the level of another national health crisis.

Of the more than 100 people who have died from drug overdoses so far this year, at least 42 deaths involved fentanyl or one of its analogs, such as carfentanil, according to data compiled by the Milwaukee County Medical Examiner’s Office. In all deaths but two, fentanyl was mixed with other drugs, usually other opioids. In 20 deaths, that opioid was heroin.

Investigators say that many who died of overdoses are not even aware that the drug they are using has been cut with fentanyl.

A recent arrest at Mayfair mall illustrates the problem. It was laid out in a criminal complaint charging 21-year-old Amari Hampton with, among other counts, felony possession with intent to deliver heroin and felony possession with intent to deliver narcotics.

According to the complaint:

On May 7, Wauwatosa police patrolling the parking lot at Mayfair mall discovered a white van with stolen license plates parked near Macy's department store.

Officers searched the van, finding a loaded handgun beneath the driver's seat. A few minutes later, Hampton and a female companion returned to the van and got inside. Police arrested them and searched the van again.

This time officers found 19.7 grams of fentanyl wrapped in a plastic bag and tucked into a cloth bag. In another bag, they found 9.3 grams of fentanyl, 23.8 grams of heroin and 2.5 grams of marijuana.

"Fentanyl is being integrated into the heroin supply," the complaint says.

"Unlike heroin, fentanyl can be cheaply manufactured — costing $2,000 to $3,000 per kilogram as compared to heroin, costing $60,000 per kilogram," it says.

While dealers stand to profit from spiking their drugs, the complaint says "the addition of fentanyl to heroin magnifies the unpredictability of the heroin's potency thus increasing the risk of an overdose."

That dealers are willing to introduce that risk without telling their customers underscores what Bell sees as their most fundamental rationale.