Opioids like oxycodone and methadone have been prescribed for pain relief since the early 1900s. But the rise of these painkillers, most notably Oxycontin, as a panacea treatment for chronic pain in the past two decades has been costly. Dr. Barth Wilsey, a physician specializing in chronic pain at the University of California Davis Medical Center, has watched their growth with increasing concern. Although he recalls only one patient death in his 17-year career, it's not an uncommon way to go: In 2010, 22,134 people died from prescription drug overdoses, a number that has quadrupled since 1999.

“In my perspective,” says Wilsey, “we've got to look for something else.”

Wilsey is trying. He's leading a clinical trial at UC Davis that will test the effectiveness of cannabis—the preferred medical term for medical marijuana—on patients suffering from spinal cord injuries. It's a small but important step forward in a field of medicine that has seen little progress in this country.

Even as states charge forward on patients’ right to cannabis, the federal government clings stubbornly to the position that cannabis is only a drug of abuse—that there simply isn't enough science to justify its application as medicine.

“There is only no science because nobody allows you to do the research,” says Donald Abrams, a cancer and integrative medicine specialist at the University of California's Osher Center for Integrative Medicine.