In a recent opinion piece, the Wall Street Journal editorial board outlined the history of the 340B program, and praised some efforts toward reform.
https://www.wsj.com/opinion/white-house-drug-price-reform-340b-hospital-lobby-e4753acf
The 340B program allows hospitals which serve Medicaid patients to benefit from discounts on pharmaceuticals prescribed for their care. The WSJ describes how the current situation has way overblown the original intent of the program, and is now affecting the entire healthcare market negatively.