Merck (MRK) Stock After Hours Today (Dec. 15, 2025): What’s Moving Shares and What to Watch Before Tuesday’s Open
Merck & Co., Inc. (NYSE: MRK) — known as MSD outside the U.S. and Canada — is ending Monday’s session (December 15, 2025) with investors focused on a mix of “quiet tape” trading, fresh analyst commentary, and a key shareholder