The company, which develops medicines using cannabis extracts, spent £43.5mln on testing and other product development activities in the year to September, a £10.8mln increase on last year.
The spending spree widened pre-tax losses to £19.6mln over the twelve months, which is nearly double last year’s loss of £10.4mln.
GW and its investors have been pumping money into advancing Epidiolex, a drug program in the field of childhood epilepsy.
Justin Gover, GW's chief executive said he expects to complete much of the Epidiolex development program by 2015 as well as start to build a US commercial presence in anticipation of future launch.
Clinical trials are set to be completed by the middle of 2016 and launch the drug in early 2017.
The firm’s flagship product is its cannabinoid prescription drug Sativex, which is approved in 27 countries outside the US to treat spasticity due to multiple sclerosis.
Sativex is in phase three clinical development as a potential treatment of pain linked to advanced cancer.
Total revenue climbed to £30mln, up from £27.3mln. Sativex product sales revenues totalled £4.4mln.
Cover added that the company is looking to progress multiple clinical trials for its cannabinoid product pipeline.
Shares were 20p lower at 372p, a drop of 5%.