People have been growing and smoking marijuana for thousands of years, but it wasn't until 1964 that anyone knew why it got you high. That year, the Israeli chemist Raphael Mechoulam isolated tetrahydrocannabinol, better known as THC, and went on to do groundbreaking studies on how and why marijuana affects the brain. But all along, he had his eye on another of cannabis' chemical components, one that he had discovered a year before: cannabidiol, or CBD.

It didn't get people high, but it seemed to have all sorts of other effects, including curbing seizures in laboratory animals and improving sleep in people with insomnia. In 1980, Mechoulam published the results of a small clinical trial showing that CBD reduced seizures in seven out of the eight epileptic patients tested, well outperforming a placebo. He expected funding for larger studies to flow in and drug companies to start calling. And then…nothing. "Nobody was interested," he remembers.

That's changing now. As more and more states legalize medical and even recreational pot, CBD is coming under research scrutiny again. The general hypothesis is that CBD is responsible for many of marijuana's therapeutic benefits but none of its downsides—like, you know, getting high. (For many patients using marijuana to treat symptoms like pain and nausea, the altered state of consciousness THC induces is an unwanted side effect.) Some states, including Alabama and Florida, have even legalized CBD for medical use while keeping THC illegal.

Scientists are scrambling to catch up with the hype. Medical marijuana is difficult to study, especially in the US. It's a Schedule 1 drug, and researchers hoping to work with it need approval from several federal agencies, including the Drug Enforcement Administration. "I think it does inhibit ordinary investigators who don't have the means or the knowledge or the staying power to get through the system," says Igor Grant, the director of University of California's Center for Medical Cannabis Research.