In the winter of 1999, Dr. Allan Frankel, a renowned internist in Los Angeles, suffered a viral infection of the heart. Doctors told him he had six months to live. He’d rarely tried marijuana, but several of his cancer and AIDS patients urged him to use it for his heart. A year later, his heart was normal. Frankel, now 66, says he can’t be certain that cannabis healed him – but it certainly helped. “I’d been depressed and cannabis stopped the depression,” he says. “It gave me something to look forward to. My brain was turned on.”

In the following years, he combed the scientific literature on cannabis, and in 2006, opened a cannabis medical practice. He developed formulas for whole plant oils with different combinations of THC, the compound in pot that gets people high, and CBD, a non-psychoactive compound that’s believed to have broad healing properties.

Working with patients, he found that many could benefit from small doses. “A quarter of my patients are taking less than 3 mg of THC a day,” he says. He calls it the “correct dose. In all medicine, with all drugs, you look for the minimum effective dose. Period.”