Merck (MRK) Stock After Hours: Key News, Analyst Calls, and What to Watch Before the Dec. 19, 2025 Market Open
Merck & Co., Inc. (NYSE: MRK) ended Thursday, December 18, 2025, on a strong note—and then barely budged after the closing bell—after a day that mixed a bullish analyst upgrade with a fresh round of healthcare-policy headlines and pipeline developments