[There are many] obstacles and frustrations scientists face in trying to study the medical uses of marijuana. Dating back to 1999, the Department of Health and Human Services has indicated it does not see much potential for developing marijuana in smoked form into an approved prescription drug. In guidelines issued that year for research on medical marijuana, the agency quoted from an accompanying report that stated, If there is any future for marijuana as a medicine, it lies in its isolated components, the cannabinoids and their synthetic derivatives." Scientists say this position has had a chilling effect on marijuana research. Though more than one million people are thought to use the drug to treat ailments ranging from cancer to seizures to hepatitis C and chronic pain, there are few rigorous studies showing whether the drug is a fruitful treatment for those or any other conditions. A major reason is this: The federal government categorizes marijuana as a Schedule 1 drug, the most restrictive of five groups established by the Controlled Substances Act of 1970. Drugs in this category - including heroin, LSD, peyote and Ecstasy - are considered to have no accepted medical use in the United States and a high potential for abuse, and are subject to tight restrictions on scientific study. In the case of marijuana, those restrictions are even greater than for other controlled substances. Marijuana remains illegal under federal law, though nearly half the states and the District of Columbia allow its medical use and two, Colorado and Washington, have legalized its recreational use.