By Hampton Sides, National Geographic

There’s nothing new about cannabis, of course. It’s been around humankind pretty much forever.

In Siberia charred seeds have been found inside burial mounds dating back to 3000 B.C. The Chinese were using cannabis as a medicine thousands of years ago. Marijuana is deeply American too—as American as George Washington, who grew hemp at Mount Vernon. For most of the country’s history, cannabis was legal, commonly found in tinctures and extracts.

Then came Reefer Madness. Marijuana, the Assassin of Youth. The Killer Weed. The Gateway Drug. For nearly 70 years the plant went into hiding, and medical research largely stopped. In 1970 the federal government made it even harder to study marijuana, classifying it as a Schedule I drug—a dangerous substance with no valid medical purpose and a high potential for abuse, in the same category as heroin. In America most people expanding knowledge about cannabis were by definition criminals.

But now, as more and more people are turning to the drug to treat ailments, the science of cannabis is experiencing a rebirth. We’re finding surprises, and possibly miracles, concealed inside this once forbidden plant. Although marijuana is still classified as a Schedule I drug, Vivek Murthy, the U.S. surgeon general, recently expressed interest in what science will learn about marijuana, noting that preliminary data show that “for certain medical conditions and symptoms” it can be “helpful.”

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