GW Pharmaceuticals was founded in 1998 by doctors Geoffrey Guy and Brian Whittle. That year, they obtained a cultivation license from the United Kingdom Home Office and the MHRA, allowing the company to cultivate, possess and supply cannabis to conduct scientific research concerning medical cannabis.
Later in 1998, GW Pharmaceuticals entered into a contract with Hortapharm B.V., a cannabis research and development corporation based in Amsterdam.
In 2001, GW Pharmaceuticals listed on the Alternative Investment Market, the junior market of the London Stock Exchange. In May 2013, the company became dual-listed on the NASDAQ and AIM.
In 2014, the company made a deal with New York to develop clinical trials using cannabidiol (CBD) to treat children who suffer from seizures and other medical complications. In May 2021, Jazz Pharmaceuticals acquired the company.