Pfizer Inc. (/ˈfaɪzər/)[3] is an American multinational pharmaceutical corporation. One of the world's largest pharmaceutical companies, it is ranked 57 on the 2018 Fortune 500 list of the largest United States corporations by total revenue.[4][5]

Headquartered in Manhattan, Pfizer develops and produces medicines and vaccines for a wide range of medical disciplines, including immunology, oncology, cardiology, endocrinology, and neurology. Its products include the blockbuster drug Lipitor (atorvastatin), used to lower LDL blood cholesterol; Lyrica (pregabalin) for neuropathic pain and fibromyalgia; Diflucan (fluconazole), an oral antifungal medication; Zithromax (azithromycin), an antibiotic; Viagra (sildenafil) for erectile dysfunction; Celebrex (also Celebra, celecoxib), an anti-inflammatory drug; and Prevnar 13, a pneumococcal conjugate vaccine.

In 2016, Pfizer Inc. was expected to merge with Allergan to create the Ireland-based "Pfizer plc" in a deal that would have been worth US$160 billion.[6] The merger was called off in April 2016, however, because of new rules from the US Department of the Treasury against tax inversions, a method of avoiding taxes by merging with a foreign company.[7] The company has made the second-largest pharmaceutical settlement with the United States Department of Justice.

On December 19, 2018, Pfizer announced a joint merger of their consumer healthcare division with UK pharma giant GlaxoSmithKline; the British company will maintain a controlling 68% of shares.[8]

Pfizer was a constituent of the Dow Jones Industrial Average from 2004 to 2020, when it was announced that the company would be replaced by Amgen in the Dow Jones. The change took effect at start of trading on August 31, 2020.[