California's health insurance exchange, Covered California, has the largest enrollment of all exchanges with Kaiser Foundation Health Plan, Blue Shield of California, and Centene as enrollment leaders. In the private commercial marketplace, Kaiser Foundation Health Plans remains dominant. The Affordable Care Act continues to be a stabilizing force in the commercial sector, but carriers doing business in the heavily regulated state struggle to find ways to contain member drug costs. The state has opted to carve out the Medicaid pharmacy benefit, taking control of the preferred drug list from managed Medicaid MCOs. Medicare Advantage members continue to see more zero-premium plans.