This is straight from www.usdoj.gov. I stumbled upon it because I'm writing a research paper on legalization/decriminalization of marijuana.
"In the case of United States v. Oakland Cannabis Club the U.S. Supreme Court ruled that marijuana has no medical value as determined by Congress"
The whole article can be read here.
http://www.jointogether.org/news/headlines/inthenews/2001/supreme-court-rules-against-3.html