The Verge

That’s what prompted Greenblatt to take a surprising approach: besides psychotherapy and medication, Greenblatt also prescribed Mary a twice-daily dose of probiotics, the array of helpful bacteria that lives in our gut. The change in Mary was nothing short of miraculous: within six months, her symptoms had greatly diminished. One year after the probiotic prescription, there was no sign that Mary had ever been ill.

Her parents may have been stunned, but to Greenblatt, Mary’s case was an obvious one. An imbalance in the microbes in Mary’s gut was either contributing to, or causing, her mental symptoms. “The gut is really your second brain,” Greenblatt said. “There are more neurons in the GI tract than anywhere else except the brain.”