Police say 35-year-old Nicholas deSpoelberch, of Darien, was arrested last week in Wilton, Connecticut.
Despoelberch is the dean of students at Regis High School.
He had heroin, prescription pills and drug paraphernalia on him at the time, according to authorities.
Police say they found deSpoelberch's 2005 Nissan Altima parked in the middle of the road on Old Highway Road, a dead-end street, around 10 p.m. on July 11. Further examination found deSpoelbergh asleep in the front seat with the car turned off.
He allegedly had glassy eyes and was talking unusually slow, and he admitted to the officer that he was under the influence of medication and in possession of pills not prescribed to him.
He was arrested for possession of narcotics, possession of drug paraphernalia and retaining prescriptions pills outside of their original container.
He has since been suspended from his job.
"We have zero tolerance for such activities, and as such Mr. deSpoelberch has been suspended pending further investigation," Regis president Philip Judge said in a statement.
The school's website lists deSpoelberch as a graduate of Sarah Lawrence College and The College of New Rochelle.