Police are searching for the source of the drug Molly (MDMA), which hospitalized 12 people at Wesleyan University on Sunday with overdose symptoms. Middletown Police Chief William McKenna described it as a “bad batch.”

According to the National Institute on Drug Abuse (NIDA), Molly is the “pure crystalline powder form” of MDMA, also known as ecstasy. It is a psychoactive drug with similarities to the hallucinogen mescaline and the stimulant amphetamine. It produces feelings of euphoria, increased energy, emotional warm and empathy toward others, as well as distortions in time and sensory perception. Although it faded from popularity in the mid-2000s, MDMA has returned as a major concern among drug-abuse prevention advocates.

Potentially dangerous side effects of using Molly include an increase in blood pressure and heart rate. Once it wears off, users can experience depression, confusion, sleep problems, anxiety and drug craving for hours or even weeks.

Another big risk with use of MDMA, even in the Molly form, is additives. A long list of additives are associated with Molly pills, according to the NIDA, all of which can cause potentially dangerous side effects when mixed either with MDMA or any other substances, such as marijuana or alcohol, that may be consumed at the same time. However the idea that Molly is a safer form of MDMA persists. The Drug Enforement Administration says that most often Molly is not pure MDMA, but a toxic mixture of lab-created chemicals.

Use of ecstasy on college campuses, which was a major concern of drug abuse prevention groups in the early 2000s, dropped off by 2006. MDMA, this time in the form of Molly, has returned to the category of dangerous campus drugs in the last two years. Two New Hampshire college students have died with symptoms consistent with an overdose of MDMA. A University of Virginia sophomore died, also linked to Molly use, and there have been several reported overdoses among Boston-area college students.

As of Monday, four of the people involved in the Wesleyan Molly overdose are still hospitalized. Police are interviewing people at a coed group house at the university. Some students said that overdose symptoms occurred after the drugs were taken at a party held at that house.