MEXICO CITY (AP) — Fifteen grade school students in Mexico have been treated after apparently taking part in an internet “challenge” in which groups of students take tranquilizers to see who can stay awake the longest.

The incident occurred Monday in the north-central city of Guanajuato. It came just days after health authorities issued a national alert about the craze. It was the fourth school in Mexico to suffer such incidents in the last year.

Guanajuato Mayor Alejandro Navarro said the students were treated at the school, and urged parents to supervise their kids’ use of social media.

“As a rule, girls and boys shouldn't have social media accounts, it's bad to start with,” Navarro wrote in his Facebook account.

There was no immediate information on the condition of the students, believed to be fifth and sixth graders, or where they got the tranquilizers.

The Health Department issued an alert on Jan. 25 about the dangers of clonazepam, a tranquilizer, and called on the public to report any store selling it without a prescription.

That alert came one week after eight students at a Mexico City middle school were treated after taking a “controlled medication.” Some were hospitalized. Just days before, three students at another middle school near the northern city of Monterrey were treated for taking doses of clonazepam.

The department warned about the social media challenge, dubbed “the last one to fall asleep wins,” calling it dangerous.