"The student said she had a pain in her wrist and distributed them," Woolf told ABCNews.com. "One girl ate [multiple] pills and the other girls took one."
The school counselor noticed one of the girls "not feeling well" in the hallway and intervened. Two other girls not involved in the incident reported that they had overheard conversations in the hall and worried the teens may have taken medicine.
"These young girls are not aware of how serious it could be," said Woolf, who called the paramedics.
The girls probably became nauseated after taking the painkillers, according to Dr. Lynn Willis, a pharmacologist from the Indiana University School of Medicine.
"The same thing would have happened to them if they had overdosed on Demerol, OxyContin or any other of the opioids," he told ABCNews.com.
Tramadol has been around since about 1977 but was approved as a nonscheduled painkiller -- the least-addictive type of drug, according to the U.S. government -- in 1995 and marketed by Ortho-McNeil Pharmaceutical as Ultram.
Doctors say its abuse record has been "fairly low," but that is changing.
"These girls were naive," said Dr. Andrew Kowal, director of the Pain Center at Lahey Clinic in Massachusetts. "They take one or two pills and it makes them feel dizzy, but you take too much and you can die."
The so-called "nonaddictive" nature of tramadol is precisely why it can be so dangerous, Kowal told ABCNews.com. Users don't get a euphoric "buzz," so they tend to take more of it.
But, like alcohol and heroin, tramadol is a central nervous system depressant and can cause respiratory distress in larger quantities. And because it has anti-depressant properties, it can cause seizures, even at lower doses.
Kowal has noticed an "increasing diversion" of tramadol in New England. "It's available on the street for purchase and it came from mom or dad's cabinet."
Tramadol also can be easily obtained over the Internet with a credit card and, on many sites, without a medical history or physician approval.
The National Institute on Drug Abuse offers advice on how parents can reduce the likelihood of children "pilfering" dangerous drugs from the medicine cabinet.
"If you're not taking it, dispose of it," said Dr. Wilson Compton, director of the institute's division of epidemiology services and prevention research. "If you need it on a regular basis, keep it locked up -- no matter how much you trust your own teen. There are others in the house."
Meanwhile, rather than be expelled, the four girls from Utah face the possibility of 45 days in a detention center under the school's Safe School policy. Their fate will be decided after they appear before a district committee with their parents.
Woolf went on student TV to warn of the dangers of prescription drugs and plans to speak before parents during a seminar. The school will also address the issue with counselors and in health classes.
"It was a very unusual situation, and that's why we acted so quickly and aggressively," said Woolf. "I really believe they took them with no knowledge of what it would do to them, just to have a nice time. Now we have to take care of the health of those students and educate others to those kinds of behaviors."