In an effort to lower the cost of medications for its 4.8 million members, a major health insurer in California is changing the prescription drug pricing system.

Instead of using CVS Health’s Caremark as its pharmacy benefit manager, Blue Shield of California will partner with Amazon Pharmacy and Mark Cuban Cost Plus Drug Company. Once the multi-year plan is fully implemented, the insurer expects to save up to $500 million in annual drug costs.

Pharmaceutical benefit managers negotiate rebates with drug manufacturers on behalf of insurers. Their opaque practices have drawn criticism from other players in the health care industry and from Congress. Specifically, critics are concerned about how companies are compensated and how their practices may increase drug costs. There are several large healthcare businesses that own big insurers as well as top benefit managers.

“The new pharmacy care model is intended to fix problems with the broken prescription drug system today,” Blue Shield said.

Currently, the pharmacy system is extremely expensive, extremely complicated, completely opaque, and designed to maximize profit instead of maximizing quality, convenience, and cost-effectiveness for consumers,” said Markovich, the insurer’s CEO. As a result, we are working with like-minded partners to develop a completely new system that gets the right drugs to the right people at the right time at a significantly lower cost.”

Members will receive free delivery of medications from Amazon Pharmacy, and Mark Cuban Cost Plus Drug Company will offer a pricing model that Blue Shield says will be “simple, transparent, and more affordable.” Additional services will be provided by two other companies.

He said the partnership with Blue Shield “will benefit their members and can have a profound effect on the industry.”

Blue Shield members with complex conditions will continue to receive specialty pharmacy services from CVS Caremark.

During the past two decades, CVS Health has provided complex, specialty medications for Blue Shield of California members who require them.

In morning trading, CVS (CVS)’ stock fell around 9%. Before Thursday’s drop, it had already fallen by more than 21% this year due to fears of competition from Amazon and other low-cost pharmaceutical companies.