There are the Sacklers, the family that controls Purdue Pharma, the maker of OxyContin. There are the doctors who ran pill mills, and the rogue pharmacists who churned out opioid orders by the thousands.

But the daunting financial muscle that has driven the spread of prescription opioids in the United States comes from the distributors — companies that act as middlemen, trucking medications of all kinds from vast warehouses to hospitals, clinics and drugstores.

The industry’s giants, Cardinal Health, McKesson and AmerisourceBergen, are all among the 15 largest American companies by revenue. Together, they distribute more than 90 percent of the nation’s drug and medical supplies.

New civil suits from the attorneys general in New York, Vermont and Washington State accuse distributors of brazenly devising systems to evade regulators. They allege that the companies warned many pharmacies at risk of being reported to the Drug Enforcement Administration, helped others to increase and circumvent limits on how many opioids they were allowed to buy, and often gave advance notice on the rare occasions they performed audits.