GW Pharma said it would receive a signature fee of 12 million pounds, within total potential milestone payments of 46 million pounds, and that it would maintain a significant share of long-term product revenues.
At 8:05 a.m., GW Pharma shares were up 14.5 percent at 134.5 pence, valuing the firm at 153 million pounds.
Almirall is Spain's largest pharmaceutical company and one of Europe's biggest private drug companies, with 2005 sales approaching 1 billion euros (673 million pounds), GW Pharma said.
GW Pharma grows thousands of marijuana plants at a secret location in the English countryside, having been granted a dispensation by the government to use the plant for medical research.
Canada became the first country to approve Sativex, an under-the-tongue spray, for sale in April 2005 as a treatment for neuropathic pain in multiple sclerosis patients.
Sativex was initially expected to be approved in Britain by the end of 2003, but has suffered numerous delays.
German drugmaker Bayer (BAYG.DE: Quote, Profile, Research) is GW Pharma's marketing partner in Canada and the UK.