Earlier this month, the United States Supreme Court ruled that federal drug laws trump policies in ten states that permit medicinal marijuana use.
The decree reignites a smoldering debate among scientists, activists, and lawmakers about how to leverage marijuana's medical benefits while minimizing its potential for abuse.
Known by the scientific name Cannabis sativa, marijuana is an annual herb closely related to the hops used in beer brewing.
Cannabis has been "used since antiquity for both herbal medication and intoxication," according to a 1999 study commissioned by the Institute of Medicine (IOM), a Washington, D.C.-based component of the National Academy of Sciences.
"There is scientific evidence that [marijuana] helps with pain relief and nausea and vomiting from chemotherapy, for example, in terminal cancer patients," said John A. Benson, Jr., a principal investigator of the IOM study and a professor of internal medicine at the University of Nebraska Medical Center.
In addition, some HIV/AIDS patients suffering from decreased appetites use marijuana to "get the munchies," another oft-noted effect of the drug.
Roger Pertwee, a professor of neuropharmacology at the University of Aberdeen's Institute of Medical Sciences in Scotland, noted that "cannabis contains lots of different chemicals called cannabinoids." The most active chemical is delta-9-tetrahydrocannabinol, or THC.
THC binds to specific receptors in the human brain to create the euphoric high associated with smoking pot.
In the early 1990s Pertwee's research group helped to uncover human-produced chemicals similar to THC that stimulate our appetites and help us control pain. "We produce our own cannabis, in effect," he said. "It often seems to have a protective role."
According to Benson, of the University of Nebraska Medical Center, the debate should not be about whether marijuana works to relieve symptoms, but how to best deliver its chemical constituents.
"Smoking is a terrible delivery system," he said. Aside from the potential risk of lung damage, the potency of smoked marijuana is difficult to measure, because THC levels vary widely from plant to plant.
Currently, a synthetic version of THC is available to cancer and HIV/AIDS patients in the U.S. as an oral drug known by the brand name Marinol. Approved by the U.S. Food and Drug Administration, the drug (dronabinol) allows patients and doctors to control the amount of active compound that is delivered.
Benson noted, however, that some patients prefer smoking pot to taking pills because the effects set in much faster. "When you inhale something into the lungs, it's very rapidly absorbed—you get an effect in five minutes," he said. "When you take a capsule, it may take an hour and a half."
THC drugs would be more effective, Benson added, if they were delivered through a fast-acting oral spray similar to asthma inhalers.
According to the 1999 IOM report, the legal status of marijuana has greatly colored the scientific debate over the plant's use in medicine.
The broad U.S. federal drug law known as the Controlled Substances Act of 1970 lists marijuana as a Schedule I substance. The designation describes drugs with a high potential for abuse and no accepted medical use. Other Schedule I drugs include heroin and LSD.
In 1972 the National Organization for the Reform of Marijuana Legislation, a nonprofit advocacy group, unsuccessfully lobbied the U.S. government to relist marijuana as a Schedule II substance. That class includes drugs such as morphine and cocaine that are highly addictive but have well-established medical uses.
Based on the IOM study, the U.S. Drug Enforcement Administration (DEA) maintains that smoked marijuana should remain a Schedule I drug. Any medical effects from smoking marijuana cigarettes can be met more effectively with approved commercial drugs, the agency says.
In fact, DEA has placed the THC drug Marinol in Schedule III—a less restrictive category—and supports research to find new delivery methods and therapeutic uses for cannabinoids.
Pertwee, of the University of Aberdeen, believes the potential for patients to become addicted to manufactured cannabinoid drugs is relatively low. However, conflicting data exist as to whether long-term THC use leads to dependency.
Benson also believes that medical marijuana, even when smoked by terminal patients, is unlikely to trigger addiction if use remains carefully monitored. "If you have a controlled distribution system for medical use, as with morphine, for example, I don't see the risk," he said.
On June 6 the U.S. Supreme Court declared that federal drug law overrides policies in ten states that allow marijuana for medical use. The ruling upholds the federal government's right to destroy homegrown plants and to arrest anyone possessing the drug, even if they are using it following a doctor's advice.
California passed the first medical marijuana law in 1996. Between 1999 and 2004, nine more states followed suit. Police in these states allow local doctors to recommend that special medical-marijuana-use licenses be issued to needy patients.
The Supreme Court's decision doesn't overturn the states' liberalized stance. But Benson believes it will affect the drug's accessibility.
"I think this ruling is going to inhibit physicians from recommending [marijuana]," he said, noting worries by some that the government could revoke doctors' licenses to prescribe other controlled substances. "But it will remain a drug purchased on the street, grown in cellars and backyards."