Tobacco firm Imperial Brands is investing in UK biotech company Oxford Cannabinoid Technologies (OCT).
The move comes as campaigning to allow marijuana products for medicinal purposes gathers pace.
A company subsidiary, Imperial Brands Ventures, is taking a stake in the UK firm, but its size is unknown.
Tobacco companies are trying to diversify away from their core product. Imperial's website bears the motto: "From tobacco to something better."
Imperial now sees itself as "a dynamic fast-moving consumer goods company borne out of a strong tobacco heritage".
OCT is a firm licensed by the UK Home Office that researches, develops and licenses cannabinoid-based compounds and therapies.
Imperial Brands' chief development officer, Matthew Phillips, said: "Our investment enables Imperial to support OCT's important research while building a deeper understanding of the medical cannabis market."
Imperial no longer makes cigarettes in the UK. Its last UK manufacturing site, the Horizon factory in Nottingham, closed down two years ago.