There is a really good description of how the Sacklers (owners of Purdue Pharma) used the marketing prowess gained from introducing valium to the market in the 1950s to push oxycontin later in this article:
https://www.newyorker.com/magazine/2017/10/30/the-family-that-built-an-empire-of-pain.
They marketed oxy as revolutionary, non-addictive alternative to normal opiate delivery systems, then lied and covered up the fact that their assurances to doctors were wrong. They also had an amazing amount of luck co-opting docs to push oxy to colleagues. Nothing like an all-expenses paid "speaking engagement" in Hawaii for a week to spread the word to colleagues. Plus a couple grand in cash as the "honorarium." Oh--and quite often , the "speaking" part of the deal got canceled, but they were very generous and never asked for the money back when that happened.
Big pharma is just as crooked as big oil or the MIL.