The incident took place at Ward Melville High School in East Setauket.
All of the students were taken to Stony Brook University Hospital with elevated heart rates.
The students were treated and released.
"The word was kids were eating brownies with pot during the lunch period. Right, that's what's come out," a parent said.
Parents arrived at a school board meeting looking for answers on Tuesday night.
"I got a robo call about cap and gown, I didn't get a robo call about toxic brownies," said Kelly Campanella, a parent.
Those toxic brownies threatened to overshadow a meeting about the school budget even though district officials say they still don't have all the facts.
"The police are investigating and we have started an internal investigation," said Dr. Jeffrey Kerman, the President of the School Board.
Between 11:30 a.m. and 2 p.m. at Ward Melville High School district officials confirmed that five students had to be transported to the hospital after experiencing symptoms that included elevated heart rate.
Officials say the symptoms developed after the students ate brownies potentially containing harmful toxins.
Officials say they don't know definitively what was baked into the brownies, but privately many here say they believe it was marijuana.
"I think that anyone that would bring drugs into school, sell them to kids or give them to kids unknowingly is a moron," a student said.
Authorities are trying to determine who is responsible.
Meanwhile some parents are withholding judgment.
"I think one needs to find more information about it until one speaks," a parent said.
The Three Village Central School District released a statement saying: "Between the hours of 11:30 a.m. and 2 p.m. five tenth-grade Ward Melville High School students were transported to Stony Brook University Hospital after experiencing symptoms, including elevated heart rate. The district believes that these symptoms were the result of the consumption of brownies potentially containing harmful toxins, which were obtained by a fellow classmate. The district's utmost concern is for the safety and well-being of these students, each of which have been released from the hospital. In addition to the police investigation, the district is conducting an internal investigation and appropriate disciplinary action will be taken as necessary."