At a party not long ago in Park Slope, Brooklyn, Kaitlin, a 22-year-old senior at Columbia University, was recalling the first time she was offered a drug called Molly, at the elegant Brooklyn home of a cultural figure she admired. “She was, like, 50, and she had been written about in the Talk of the Town,” said Kaitlin, who was wearing black skinny jeans and a tank top. “This woman was very smart and impressive.”

At one point, the hostess pulled Kaitlin aside and asked if she had ever tried the drug, which is said to be pure MDMA, the ingredient typically combined with other substances in Ecstasy pills. “She said that it wasn’t cut with anything and that I had nothing to worry about,” said Kaitlin, who declined to give her last name because she is applying for jobs and does not want her association with the drug to scare off potential employers. “And then everyone at the party took it.”

Since that first experience, Kaitlin has encountered Molly at a birthday celebration and at a dance party in Williamsburg. “It’s the only drug I can think of that I have to pay for,” she said. “It makes you really happy. It’s very loose. You just get very turned on — not even sexually, but you just feel really upbeat and want to dance or whatever.”

Molly is not new, exactly. MDMA, or 3,4-methylenedioxy-N-methylamphetamine, was patented by Merck pharmaceuticals in 1914 and did not make much news until the 1970s, when psychotherapists began giving it to patients to get them to open up. It arrived at New York nightclubs in the late 1980s, and by the early ’90s it became the preferred drug at raves at Limelight and Shelter, where a weekly party called NASA later served as a backdrop in Larry Clark’s movie “Kids.”