Dennis Sponer writes for WorkersCompensation.com:

Physician dispensing—the practice of physicians providing medications directly from their offices rather than through licensed pharmacies—has
evolved into a commercial model that reliably drives higher drug costs while circumventing the utilization controls embedded in the traditional
pharmacy channel. What began as a limited convenience has become a material and persistent cost driver within the workers’ compensation
pharmacy system...

The price premium is one of the main reasons physician dispensing remains so pernicious. The fact is that these incentives translate into significantly higher costs. The Workers’ Compensation Research Institute (WCRI) found that physician-dispensed drugs cost, on average, between 60% and more than 300% more than identical medications dispensed through retail pharmacies. In states where physician dispensing is permitted, it can account for as much as 20% to 45% of total workers’ compensation drug spend. While limited in-office dispensing may occasionally benefit injured workers immediately following an injury or in remote settings, industry analyses show that the practice more often results in substantially higher costs, reduced clinical oversight, inappropriate utilization, and poorer overall claim outcomes. 

You can read the full article here.  

He references the WCRI articles The Impact of Physician Dispensing on Opioid Use (2014), WCRI Research Brief: A Multistate Perspective on Physician Dispensing 2011-2014 (2017), and Are Physician Dispensing Reforms Sustainable? (2015).  Also potentially of interest is WCRI's more recent study of Interstate Variation and Trends in Workers’ Compensation Drug Payments, 5th Edition., which includes analysis of physician dispensing.