(CNN) -- Over the last year, I have been working on a new documentary called "Weed." The title "Weed" may sound cavalier, but the content is not.
I traveled around the world to interview medical leaders, experts, growers and patients. I spoke candidly to them, asking tough questions. What I found was stunning.
Long before I began this project, I had steadily reviewed the scientific literature on medical marijuana from the United States and thought it was fairly unimpressive. Reading these papers five years ago, it was hard to make a case for medicinal marijuana. I even wrote about this in a TIME magazine article, back in 2009, titled "Why I would Vote No on Pot."
For the rest of the story: http://edition.cnn.com/2013/08/08/health/gupta-changed-mind-marijuana/index.html