Who is most responsible for the supply of opioids in U.S.? Well, it's definitely a "drug cartel".
From the ArsTechinca article above, the House Energy and Commerce committee holds the pharmaceutical companies responsible.
Quotes the ArsTechnica article above:
"For instance, drug companies collectively poured 20.8 million hydrocodone and oxycodone pills into the small city of Williamson, West Virginia, between 2006 and 2016, according to a set of letters the committee released Tuesday. Williamson’s population was just 3,191 in 2010, according to US Census data."
"...in Kermit, West Virginia, a town of just 406 people, the company [Miami-Luken] delivered 6.3 million hydrocodone and oxycodone pills between 2005 and 2011. For just the year of 2008, the numbers work out to Miami-Luken providing 5,624 opioid painkiller pills for every man, woman, and child in the town, the committee notes...."