Published in the journal Clinical Gastroenterology and Hepatology, a total of 21 subjects were studied that had been unresponsive to other treatments for Crohn's Disease. Half were administered a placebo cigarette and half were treated with THC rich cigarette. It was found that in those who were treated with smoked, THC rich cigarettes saw a 100 point decrease in their CDAI (Crohn’s Disease and activity index) which is the standard measure of severity of this disease.
Beyond the fact that all participants that received THC rich cigarette treatments seeing an average of a 100 point drop in their CDAI scores, five  of the participants reported complete remission of the disease, (represented by a 150 point reduction in their CDAI scores). This shows that even as a smoked joint, marijuana has clear and undeniable medical benefits, at very least, to those suffering from Crohn's Disease. Irritable Bowel Syndrome (IBS) is another bowel disease that has been reported to ease with marijuana treatments. Several States that have medical marijuana programs include IBS in their list of illnesses that can be treated using medicinal marijuana.
According to the LA Times, as recently as January, 2013, US Justices denied activist appeals against the Schedule I designation of cannabis, (putting it in the same boat as heroin and crack; "no accepted medicinal value" and "high risk of abuse"). Instead, the Justices ruled in favor of the DEA's judgement that cannabis should remain a Schedule I drug. LA Times reported,
Judge Harry Edwards, writing for the Court of Appeals for the District of Columbia, said the judges did not dispute that "marijuana could have some medical benefits." Instead, he said, they were not willing to overrule the DEA because they had not seen large "well-controlled studies" that proved the medical value of marijuana. ~ LA Times