Ten Wesleyan University students and two campus visitors were hospitalized in Connecticut over the weekend with “overdose symptoms consistent with the use of the drug Molly (MDMA),” school spokeswoman Lauren Rubenstein told the Hartford Courant. Of the 12 hospitalized individuals, two were in critical condition.

Police are looking into the source of the drug, which Middletown Police Chief William McKenna described to the Associated Press as a “bad batch,” adding: “Our first and foremost goal is to obtain information on the batch of Molly that was distributed to the students on the campus.”

According to the Courant:

Wesleyan officials did not say whether the students had been together or where the drugs had come from.

In a letter distributed to students on Monday, Wesleyan President Michael S. Roth wrote: “I ask all students: Please, please stay away from illegal substances the use of which can put you in extreme danger. One mistake can change your life forever.”

Although MDMA faded from the public conversation about drug use during the mid-2000’s, it’s come back as a major concern among drug-abuse prevention advocates.

And it’s become especially concerning to college administrators.

What is Molly, and why is it so dangerous?

Molly is the “pure crystalline powder form” of MDMA, which is also the active ingredient in ecstasy, the National Institute on Drug Abuse explains. Users take it for the euphoric and empathetic state it often produces, which can last three to six hours.

But there are potentially severe side effects. MDMA is a stimulant, so it increases the heart rate and blood pressure. The drug effectively releases a large amount of seratonin into the body at once, meaning that once the high wears off, users can experience “confusion, depression, sleep problems, drug craving, and anxiety” for hours, days, or even weeks after use, according to the NIDA.

There’s another big risk with MDMA, even in the “pure” Molly form: additives.

Although ecstasy tablets have long been known to contain additives, the NIDA warns that the same substances can appear in Molly pills, too. Here’s their list of additives found in these drugs: “ephedrine (a stimulant), dextromethorphan (a cough suppressant), ketamine, caffeine, cocaine, methamphetamine, or even, most recently, synthetic cathinones (the psychoactive ingredients in ‘bath salts’).” All can cause potentially dangerous side effects when mixed with MDMA, or with any other substances (like alcohol or marijuana) consumed at the same time.

Still, the idea that Molly is a safer form of MDMA persists, and hardly just among adolescents and college students. A 2013 story in the New York Times noted that the Molly version of MDMA “has found a new following in a generation of conscientious professionals who have never been to a rave and who are known for making careful choices in regard to their food, coffee and clothing.”

It’s impossible to prove causality, but the rise of Molly as a more socially acceptable drug in some circles has coincided with its increasing prevalence in pop culture. Nowhere is that more apparent than in song lyrics, from the likes of Miley Cyrus, Tyga and Trinidad James, whose “popped a Molly/I’m sweatin'” line made it onto the lips of LeBron James.

When did Molly become a college campus problem?

Although drug abuse prevention groups have expressed concern about MDMA use on campuses for years, that concern was primarily about ecstasy and its use in clubs and at all-night “raves,” especially among students who were already heavy multi-drug users. In a 2006 pamphlet, the Department of Education noted that the percentage of students using ecstasy or other club drugs was “relatively low” and falling. Ecstasy usage over a 30-day span among college kids was at 2.5 percent in a 2000 Monitoring the Future study, but dropped to 0.6 percent in 2006.

However, student deaths attributed to MDMA — this time in Molly form — brought it back into the discussion of risky campus drug use at the beginning of the 2013 school year. Two New Hampshire college students died at concerts, with symptoms consistent with an MDMA overdose.

There were also several reported overdoses among college-aged individuals in the Boston area, and a University of Virginia sophomore’s death at around the same time was also linked to Molly use.

How have campuses responded?

Many New England campuses built resources to discuss the drug with their students, and sent out information about the dangers of Molly use, the Huffington Post reported at the time. Pat Ketcham, president of the board of directors at the American College Health Association, told the Chronicle of Higher Education in 2013 that MDMA “has fallen off our radar a little bit and now recently is back on.”

Since then, facing some evidence that Molly is becoming increasingly popular among students, many colleges have increased awareness among students of the drug, particularly its potential adverse effects.

That’s appropriate, given one of the factors Monitoring the Future tracks in order to anticipate increases in popularity among specific drugs: People have a tendency to forget the adverse effects of a drug as it declines in popularity, paradoxically opening up the risk that it could then become more popular. “In the 2000’s we have seen drug use subside to some degree, which once again has created the conditions for generational forgetting of the dangers of many of these drugs,” the 2013 report on college drug use writes.

How widespread is Molly use?

MDMA, like many drugs, has come in and out of popularity through the years, but the percentage of users has always remained relatively low. Data indicates that there was a surge in MDMA use from about 1999 to 2001, before rates fell sharply. And that surge itself followed a few years of declined usage in the mid to late ’90s.

In addition to the increased attention on Molly incidents at colleges, there is some statistical evidence to suggest that Molly use is increasing. In 2013, the Drug Abuse Warning Network reported a sharp rise in MDMA-related hospitalizations between 2005 and 2011 among people 21 and under. In 2005, there were 4,460 estimated visits; in 2011, the estimated number jumped to 10,176 visits.

The 2013 New York Times piece on Molly also has some evidence suggesting that the drug is rising in demand, citing U.S. Customs and Border Protection data. The agency reported 2,670 MDMA confiscations in 2012, compared to 186 in 2008.

However, the annual Monitoring the Future data hasn’t quite caught up to the perception that MDMA has made a big comeback on campus: The most recent data on college students is from 2013, and the report doesn’t even contain the word “Molly.” (A 2014 Monitoring the Future report on high school student drug use notes that the study began asking about “Molly” usage for the first time in 2014.)

As for usage rates, the study’s authors note that in 2009, they warned that a decrease in the perceived risk of the drug could lead to yet another rebound. “There was some evidence that just such a rebound was occurring, at least through 2010 or 2011, but there was no further increase in 2012 and 2013,” they write. As of 2013, 0.8 percent of college students reported using ecstasy over a 30-day period.