Shares in GW Pharmaceuticals soared yesterday after the group said that it had signed a $273 million (£140 million) deal with a Japanese drug company to market its cannabis-based drug Sativex in the US.

GW, which has special permission from the UK Government to use cannabis to make pharmaceuticals, will be paid an initial fee of $18 million by its new partner, the privately held Otsuka Pharmaceuticals. The rest will be made available to GW in milestone payments.

Sativex is used to treat patients suffering from cancer pain, multiple sclerosis and other diseases of the central nervous system.

Under the terms of the deal, GW has granted Otsuka exclusive rights to develop and market the oral spray-based drug, which is GW’s lead product, in the US. GW will be responsible for the manufacture and supply of the drug to Otsuka.

Both companies hope to develop other cannabis-based drugs, known as cannabinoids, for a range of conditions.

“Otsuka’s scientists consider cannabinoids to be a significant potential source of new medicines and GW represents the ideal partner,” said Taro Iwamoto, Otsuka’s president. “Otsuka is committed to maxi-mizing the potential of Sativex in the US market and looks forward to exploring a range of longer-term cannabinoid product opportunities.”

Sativex has been approved for treating neuropathic pain in Canada, and European regulators are considering whether to approve it for MS spasticity. It is also entering trials in the US for treating cancer pain.

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