When President Barack Obama signed a law last week banning bath salts and 31 other synthetic substances, Dr. Rani G. Whitfield of Baton Rouge, La., was just one of several medical doctors who breathed a sigh of relief.

“I’ve been practicing medicine for 12 years, and I’ve never seen anything like this,” he said. “When problems began surfacing in the emergency room a little over a year ago, we were seeing psychotic episodes and extreme agitation. The kids were telling us about a new drug called ‘bath salts.’ We didn’t know what it was. They were like, ‘No, it’s not what you put in your water. It’s not ‘Calgon take me away.’”