GSK plc (an abbreviation of its former name GlaxoSmithKline plc) is a British multinational pharmaceutical and biotechnology company. It was established in 2000 by a merger of Glaxo Wellcome and SmithKline Beecham, which was itself a merger of a number of pharmaceutical companies around the Smith, Kline & French firm. It is headquartered in London, England.
GSK is the tenth-largest pharmaceutical company in the world by earnings, $9.32 billion in 2025 with $42.4 billion in revenues in the same period. As of February 2026 it is the 175th most valuable company in the world and the 12th most valuable pharmaceutical company with a market capitalisation of $122.6 billion. It was also ranked 388th on the 2025 Fortune Global 500.
The company has a primary listing on the London Stock Exchange and is a constituent of the FTSE 100 Index, the eighth largest on the London Stock Exchange behind British pharmaceutical rival AstraZeneca, which occupies the No 1 spot in London at a value of $325 billion, 2.7x more than GSK .
The company developed the first malaria vaccine, RTS,S, which it said in 2014, it would make available for five per cent above cost. Legacy products developed at GSK include several listed in the World Health Organization's List of Essential Medicines, such as amoxicillin, mercaptopurine, pyrimethamine, and zidovudine.
In 2012, under prosecution by the United States Department of Justice (DoJ) based on combined investigations of the Department of Health and Human Services (HHS-OIG), FDA and FBI, primarily concerning sales and marketing of the drugs Avandia, Paxil and Wellbutrin, GSK pleaded guilty to promotion of drugs for unapproved uses, failure to report safety data and kickbacks to physicians in the United States and agreed to pay a US$3billion (£1.9bn) settlement. It was the largest health-care fraud case to date in the US and the largest settlement in the pharmaceutical industry.
History Glaxo Wellcome
Glaxo Joseph Nathan and Co. was founded in 1873, as a general trading company in Wellington, New Zealand, by a Londoner, Joseph Edward Nathan.R. P. T. Davenport-Hines, Judy Slinn, Glaxo: A History to 1962, Cambridge University Press, 1992, pp. 7–13. In 1904, it began producing a dried-milk baby food from excess milk produced on dairy farms near Bunnythorpe. The resulting product was first known as Defiance, then as Glaxo (cf. Greek galaxias, "milky"), and was sold with the slogan "Glaxo builds bonnie babies."David Newton, Trademarked: A History of Well-Known Brands, from Airtex to Wright's Coal Tar, The History Press, 2012, p. 435. The Glaxo Laboratories sign is still visible on what is now a car repair shop on the main street of Bunnythorpe. The company's first pharmaceutical product, released in 1924, was vitamin D.
Glaxo Laboratories was incorporated as a distinct subsidiary company in London in 1935.New "Glaxo" Company. The Times, Tuesday, 15 October 1935; pg. 22; Issue 47195 Joseph Nathan's shareholders reorganised the group's structure in 1947, making Glaxo the parentJ. Nathan And "Glaxo" Reorganization. The Times, Wednesday, 8 January 1947; pg. 8; Issue 50653 and obtained a listing on the London Stock Exchange.Joseph Nathan & Co. The Times, Thursday, 20 February 1947; pg. 8; Issue 50690 Glaxo acquired Allen & Hanburys in 1958. The Scottish pharmacologist David Jack was hired as a researcher for Allen & Hanburys a few years after Glaxo took it over; he went on to lead the company's research and development (R&D) until 1987. After Glaxo bought Meyer Laboratories in 1978, it began to play an important role in the US market. In 1983, the American arm, Glaxo Inc., moved to Research Triangle Park (US headquarters/research) and Zebulon (US manufacturing) in North Carolina.
Burroughs Wellcome Burroughs Wellcome & Company was founded in 1880, in London by the American pharmacists Henry Wellcome and Silas Burroughs. The Wellcome Tropical Research Laboratories opened in 1902. In the 1920s, Burroughs Wellcome established research and manufacturing facilities in Tuckahoe, New York,"Addition to Factory" , The Eastchester Citizen-Bulletin, 19 November 1924Peter Pennoyer, Anne Walker, The Architecture of Delano & Aldrich, W. W. Norton & Company, 2003, p. 188. which served as the US headquarters until the company moved to Research Triangle Park in North Carolina in 1971."Iconic Burroughs Wellcome Headquarters Open for Rare Public Tour" , Triangle Modernist Houses, press release, 8 October 2012. The Nobel Prize winning scientists Gertrude B. Elion and George H. Hitchings worked there and invented drugs still used many years later, such as mercaptopurine. In 1959, the Wellcome Foundation bought Cooper, McDougall & Robertson Inc to become more active in animal health.
When Burroughs Wellcome decided to move its headquarters, the company selected Paul Rudolph to design its new building. The Elion-Hitchings Building "was celebrated worldwide when it was built," according to Paul Rudolph Heritage Foundation president Kelvin Dickinson. Alex Sayf Cummings of Georgia State University wrote in 2016, that the "iconic building helped define the image of RTP," saying, "Love it or hate it, Rudolph's design remains an impressively audacious creative gesture and an important part of the history of both architecture and Research Triangle Park." United Therapeutics, which bought the building in 2012, announced plans in 2020, to tear it down.
Merger Glaxo and Wellcome merged in 1995, to form Glaxo Wellcome plc. The merger was then considered the biggest in the UK corporate history. Glaxo Wellcome restructured its R&D operation that year, cutting 10,000 jobs worldwide, closing its R&D facility in Beckenham, Kent, and opening a Medicines Research Centre in Stevenage, Hertfordshire. Also that year, Glaxo Wellcome acquired the California-based Affymax, a leader in the field of combinatorial chemistry.
By 1999, Glaxo Wellcome had become the world's third-largest pharmaceutical company by revenues (behind Novartis and Merck), with a global market share of around 4 per cent. Its products included Imigran (for the treatment of migraine), salbutamol (Ventolin) (for the treatment of asthma), Zovirax (for the treatment of coldsores), and Retrovir and Epivir (for the treatment of AIDS). In 1999, the company was the world's largest manufacturer of drugs for the treatment of asthma and HIV/AIDS. It employed 59,000 people, including 13,400 in the UK, had 76 operating companies and 50 manufacturing facilities worldwide, and seven of its products were among the world's top 50 best-selling pharmaceuticals. The company had R&D facilities in Hertfordshire, Kent, London and Verona (Italy), and manufacturing plants in Scotland and the north of England. It had R&D centres in the US and Japan, and production facilities in the US, Europe and the Far East.
SmithKline Beecham Beecham
In 1848, Thomas Beecham launched his Beecham's Pills laxative in England, giving birth to the Beecham Group. In 1859, Beecham opened its first factory in St Helens, Lancashire. By the 1960s, Beecham was extensively involved in pharmaceuticals and consumer products such as Macleans toothpaste, Lucozade and synthetic penicillin research.
SmithKline
John K. Smith opened his first pharmacy in Philadelphia in 1830. In 1865, Mahlon Kline joined the business, which 10 years later became Smith, Kline & Co. In 1891, it merged with French, Richard and Company, and in 1929, changed its name to Smith Kline & French Laboratories as it focused more on research. Years later it bought Norden Laboratories, a business doing research into animal health, and Recherche et Industrie Thérapeutiques in Belgium in 1963, to focus on vaccines. The company began to expand globally, buying seven laboratories in Canada and the United States in 1969. In 1982, it bought Allergan, a manufacturer of eye and skincare products.
Smith Kline & French merged with Beckman Inc. in 1982, and changed its name to SmithKline Beckman. In 1988, it bought International Clinical Laboratories.
Merger In 1989, SmithKline Beckman merged with Beecham Group to form SmithKline Beecham P.L.C.. The headquarters moved from the United States to England. To expand R&D in the United States, the company bought a new research center in 1995; another opened in 1997, in England at New Frontiers Science Park, Harlow.
2000: Glaxo Wellcome and SmithKline Beecham merger Glaxo Wellcome and SmithKline Beecham announced their intention to merge in January 2000. The merger was completed on 27 December that year, forming GlaxoSmithKline (GSK). The company's global headquarters were at GSK House, Brentford, London, officially opened in 2002, by then-Prime Minister Tony Blair. The building was erected at a cost of £300million and was home to 3,000 administrative staff.
2001–2010
GSK completed the acquisition of New Jersey–based Block Drug in 2001, for . In 2006, GSK acquired the US-based consumer healthcare company CNS Inc., whose products included Breathe Right nasal strips and FiberChoice dietary supplements, for US$566million in cash.
Chris Gent, previously CEO of Vodafone, was appointed chairman of the board in 2005. GSK opened its first R&D centre in China in 2007, in Shanghai, initially focused on neurodegenerative diseases. Andrew Witty became the chief executive officer in 2008."Corporate Executive Team", GlaxoSmithKline. Retrieved 16 November 2013. Witty joined Glaxo in 1985, and had been president of GSK's Pharmaceuticals Europe since 2003."Andrew Witty's journey from Graduate to GSK CEO" , GlaxoSmithKline, 12 August 2008; "Andrew Philip Witty", Bloomberg.
In 2009, GSK acquired Stiefel Laboratories, then the world's largest independent dermatology drug company, for . In November 2009, the FDA approved GSK's vaccine for 2009 H1N1 influenza protection, manufactured by the company's ID Biomedical Corp in Canada. Also in November 2009, GSK formed a joint venture with Pfizer to create ViiV Healthcare, which specializes in HIV research. In 2010, the company acquired Laboratorios Phoenix, an Argentine pharmaceutical company, for US$253m, and the UK-based sports nutrition company Maxinutrition for £162million (US$256million).
2011–2022 In 2011, in a US$660-million deal, Prestige Brands Holdings took over 17 GSK brands with sales of US$210million, including BC Powder, Beano, Ecotrin, Fiber Choice, Goody's Powder, Sominex and Tagamet. In 2012, the company announced that it would invest £500million in manufacturing facilities in Ulverston, northern England, designating it as the site for a previously announced biotech plant. In May that year it acquired CellZome, a German biotech company, for US$98million,European Biotechnology News 16 May 2012. GSK acquires Cellzome 100%: Britain's largest drugmaker GlaxoSmithKline will pay about €75m in cash to acquire Cellzome AG completely ; John Carroll for FierceBiotech 15 May 2012 GSK snags proteomics platform tech in $98M Cellzome buyout and in June, worldwide rights to alitretinoin (Toctino), an eczema drug, for US$302million.John Carroll for FiercePharma. 12 June 2012 GSK continues deal spree with $302M pact for Basilea eczema drug ; Basilea Pharmaceutica Press Release. 11 June 2012 Basilea enters into global agreement with Stiefel, a GSK company, for Toctino (alitretinoin) In 2013, GSK acquired Human Genome Sciences (HGS) for US$3billion; the companies had collaborated on developing the lupus drug Belimumab (Benlysta), albiglutide for type 2 diabetes, and darapladib for atherosclerosis, and in September, sold its beverage division to Suntory. This included the brands Lucozade and Ribena; however, the deal did not include Horlicks.