CVS is the sole supplier of drugs for many "managed care" medical plans, and gouges both the patients and the plans.

Furthermore, it tries to stop states from publishing the data to show how much it gouges.

There has been a lot of concentration in the pharmacy business in the US. That surely helped put CVS in a position to do this. Thus, it is misguided to judge business mergers in terms of direct, short-term effect on the retail price of their products. A large company is ipso facto dangerous.