http://www.nytimes.com/2010/01/19/health/policy/19marijuana....
[If] a researcher wants to use a variety of marijuana that the University of Mississippi does not grow -- and there are many with differing medicinal properties -- they are out of luck, Dr. Doblin said.
"As the National Institute on Drug Abuse, our focus is primarily on the negative consequences of marijuana use," said Shirley Simson, a spokeswoman for the drug abuse institute, known as NIDA. "We generally do not fund research focused on the potential beneficial medical effects of marijuana."
NIDA controls the supply, the strains available and the research on a proposal-by-proposal basis. They admit that their first priority is not accurate science, via their active discriminating against research into beneficial effects.
While I'm not going to declare all the research they've allowed is necessarily bad, it's clearly limited and incomplete to a dysfunctional degree.
[1]Source: Claudia Little in Psychedelic Salon podcast 218: http://bit.ly/doBrGA.
This non action is the opposite of leadership, and the Department of Justice taking a slightly less conservative stance on the issue isn't progress.
Since I have found a contrary statement, in a publication that I would expect to tell me the truth on this issue,
http://hightimes.com/news/ht_admin/295
"DEA OKs MEDICAL-MARIJUANA TRIALS
"Tue, Jun 11, 2002 12:00 am
"Peter Gorman WASHINGTON After nearly 20 years of refusing to approve a single medical-marijuana human research trial, the Drug Enforcement Administration has simultaneously approved three individual trials. All three patient trials will involve the use of smoked marijuana, and be conducted at the University of California's Center for Medicinal Cannabis Research (CMCR), at its San Diego and San Francisco campuses. The marijuana used will be supplied by the National Institute on Drug Abuse's (NIDA) federally approved Hattiesburg, Mississippi pot farm."
I would expect you to back up that statement if you want us to believe it.
I see from the expected Google Scholar search
http://scholar.google.com/scholar?q=marijuana trials
that marijuana clinical trials are going on somewhere, so if there is demonstrable medical benefit from taking marijuana that is not available from some other drug, the scientific community will eventually hear about it.