It seems absolutely as straigtforward as I wrote. From that article:
"American drug and law-enforcement officials, concerned about the dramatic surge in overdose deaths from pharmaceutical opioids (165,000 from 1999 to 2014), cracked down on both legal and illegal distribution, opening the door for Mexican heroin, which sold for five to ten bucks a dose"
A trusted source of a heroine-like drug was removed, so the cartels increase production of heroine. But fentanyl is more profitable, and
"The cartels mix fentanyl with heroin because once an addict has shot that mix, they won't go back to "just heroin," since they can't get high on it anymore."
"American drug and law-enforcement officials, concerned about the dramatic surge in overdose deaths from pharmaceutical opioids (165,000 from 1999 to 2014), cracked down on both legal and illegal distribution, opening the door for Mexican heroin, which sold for five to ten bucks a dose"
A trusted source of a heroine-like drug was removed, so the cartels increase production of heroine. But fentanyl is more profitable, and
"The cartels mix fentanyl with heroin because once an addict has shot that mix, they won't go back to "just heroin," since they can't get high on it anymore."
and we end up with a much more dangerous product.