A deal between the two would create a health-services giant and a bigger competitor for UnitedHealth Group Inc., which is the largest U.S. health insurer and has its own own clinics and a pharmacy-benefits unit.

The deal comes as Express Scripts, a pharmacy benefit manager (PBM), is facing challenges on a number of fronts, including the possible loss of its largest customer, health-insurance giant Anthem Inc.

If the online retail giant does enter the pharmacy market, it would pose an immediate near-term threat to retail pharmacy chains such as CVS Health Corp. and Walgreens Boots Alliance Inc.

Walgreens Boots Alliance Inc. clinched regulatory approval for a deal to buy Rite Aid Corp. stores, a hard-fought victory following two years of failed attempts.

Amid an outbreak of dangerous infections by pain drug abusers, the U.S. FDA has asked Endo to stop sales of its powerful opioid painkiller Opana ER.

A 15-month fight between Anthem and Express Scripts spilled into public view as the companies spar over whether or not the insurer will renew its PBM contract.

Seemingly inexplicable pricing is widespread in the U.S. market for generic antibiotics. Recently, the DOJ gave a possible explanation for spiraling prices of at least some drugs.

While Mylan says its discounts were consistent with federal guidance, the government says the company owed bigger discounts on EpiPen.