Merck says its board of directors approved the buyback of up to $5 billion in common stock for the drug developer's treasury.
The company, based in Whitehouse Station, N.J., says the purchases have no time limit. Overall, the company is now authorized to buy back up to $6.4 billion in common stock.
Merck has about 3.08 billion shares of common stock outstanding.
Shares closed at $35.06 Tuesday.