Two simple avenues of research to follow would be Health Canada, our nation being the first in the world to approve Sativex for prescription to adults with MS. They might be able to provide you with some of the trial study publications for Sativex. On an added note, the Health Canada guidelines for drug approval are usually far more stringent than US FDA and their criteria for acceptance. Quite likely, if Canada says it's okay, Argentina will likely follow suit.
And quite simply, as GW Pharmecetucals. Every drug company keeps a list of where their products have appeared in respective medical journals. Most all of those studies can be purchased, but the abstract alone will indicate an efficacy or not.
If you haven't found it already, try NCBI at http://www.ncbi.nlm.nih.gov/
and search within the PubMed section of their database. There are both full studies and study abstracts available to read. If there are any paid studies that you may be interested in reading, ask your largest local library if they're connect to the EBSCO database. Their resident book worm geek should be able to show you through the specifics of accessing those database publications they subscribe to (with your tax dollars), a wealth of information that makes Google look lame.
Just be prepared to read, a lot.