CNN’s Chief Medical Correspondent Dr. Sanjay Gupta reversed his position on marijuana’s health benefits and apologized for his previous stand against it in an article Thursday for CNN. In 2009, Gupta penned an op-ed advocating against marijuana, where he advised as a doctor that “marijuana isn’t really very good for you.” At the time, he was in the running for an appointment to Surgeon General.

Since then, additional research and his work on a documentary have convinced him otherwise.

“I apologize because I didn’t look hard enough, until now,” he said. “I didn’t look far enough. I didn’t review papers from smaller labs in other countries doing some remarkable research, and I was too dismissive of the loud chorus of legitimate patients whose symptoms improved on cannabis.”

More: Sanjay Gupta Reverses on Marijuana: ‘We Have Been Terribly and Systematically Misled’