Ten students with "medical complaints" were reported Thursday at Van Nuys Middle School, with seven of them transported to hospitals, Los Angeles fire officials said.
The incident was reported around 10:30 a.m. at the school in the 5000 block of Vesper Lane.
An L.A. Fire Department official said 10 students ages 12 to 14 were evaluated for suspected overdoses and found to be in "mild to moderate distress." Seven were transported to local hospitals, and three were released at the scene.
Dozens of firefighters and police officers searched the school to ensure there were no students unaccounted for.
"Crews on scene confirmed that this was NOT fentanyl-related. Specifics of the medical complaints and possible substance(s) used will be completed by hospital personnel," the Fire Department said in a statement.
In a statement, a Los Angeles Unified School District spokesperson said the campus remained "safe and open for instruction."
"Today, we were made aware of a group of students who suffered a medical incident at Van Nuys Middle School," the spokesperson said in the statement. "In an abundance of caution, we requested medical assistance."
LAFD Capt. Erik Scott said the students possibly ingested "edibles" but added that the investigation was ongoing.
"It was not opioids; we didn't have to administer Narcan," Scott said outside the school.
Emergency officials prepared for a mass casualty event when they arrived as officials located several more sick students. Officials searched the campus for more patients but didn't find any more.
By 1 p.m. Thursday, fire engines and other emergency vehicles were still present at the school and students' voices could be heard on campus.
A parent who did not want to be identified said he spoke to his 12-year-old daughter and she was not worried.
The parent had received an email regarding the situation and was told that his child would remain at the school for the rest of the day.
But some parents still wished to bring their children home.
Several parents handed blue check-out slips and their photo IDs to school officials at a side gate. School lets out at 3 p.m.
School officials scrolled through a laptop on a coffee table to find the student.
Christopher Angel, a 12-year-old 7th grader, walked out with his mother, Angela Valle.
"Only three people were drugged in my class," he said.
Angel said he heard the students ate edibles and he saw them in his science class.
"They were acting weird, tired, high," he said.
School officials repeatedly told parents that their children were safe.
"Your children are fine in the classroom," one school official said as he handed out blue slips.
Karla Rivera waited outside the school about an hour before students would be let out.
She said she was not immediately notified by the school about the medical emergency. She said her 12-year-old son called her.
"He told me something happened," Rivera said. "He thought it was someone trying to break into the school."
An hour later, Rivera said, she received an automated call from the school telling her about the medical emergency.
"I immediately thought of fentanyl," Rivera said. "The school has done a very poor job of communicating of what is going on."
Times staff writer Howard Blume contributed to this report.
This story originally appeared in Los Angeles Times.