Cigna (CI) reported earnings Friday and the stock dropped 2.9%. Management guidance for 2019 earnings missed Wall Street’s expectations. Analysts had predicted the company would earn $16.75 per share this year, and management said $16.25 is more likely.

That wasn’t the biggest news of the day for the Nation’s largest pharmacy benefit manager, however. U.S. Department of Health and Human Services proposed a new rule intended to lower prescription drug prices for seniors. The rule has the potential to crimp profits at Cigna...