FOR DECADES, RESEARCHERS HAVE KNOWN OF THE CONNECTION BETWEEN THE BRAIN AND THE GUT Her parents were running out of hope. Their teenage daughter, Mary, had been diagnosed with a severe case of obsessive-compulsive disorder (OCD), as well as ADHD. They had dragged her to clinics around the country in an effort to thwart the scary, intrusive thoughts and the repetitive behaviors that Mary felt compelled to perform. Even a litany of psychotropic medications didn’t make much difference. It seemed like nothing could stop the relentless nature of Mary’s disorder.