Dr. Sanjay Gupta, American neurosurgeon (Photo credit: Wikipedia)

By Dr. Sanjay Gupta

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.”

Well, I am here to apologize.

I apologize because I didn’t look hard enough, until now. 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.

Instead, I lumped them with the high-visibility malingerers, just looking to get high. I mistakenly believed the Drug Enforcement Agency listed marijuana as a schedule 1 substance because of sound scientific proof. Surely, they must have quality reasoning as to why marijuana is in the category of the most dangerous drugs that have “no accepted medicinal use and a high potential for abuse.”

Read More Dr. Sanjay Gupta: Why I changed my mind on weed – CNN.com.