He added that the three worst words a parent can say are: "Not my child."
Gamarello, at Daytop, said parents should remain alert and engaged.
"They would certainly notice a change in behavior, some kind of withdrawal from activities their kids were involved in, failing grades, cutting classes, a disinterest in family activities ... a change in friends, basic changes in social activities. Maybe they went out and went to the movies, maybe they played sports, and now they are going to someone's house for a party."
Parents should have a conversation with their children about what they are witnessing, talk to a counselor at school and have their children evaluated.
"The really important thing is for them just to be involved and not ignore signs," Gamarello said.
Natalie went into rehab after what she described as an Ambien-fueled "day of hell." Her friends had already threatened to cut her off because of her drug use. A week later, the thought of losing those friends drove her to enroll in an intensive outpatient rehabilitation program, she said.
Natalie has been clean for nearly two years, she said.
She is earning good grades, but her overall grade-point average may not be high enough for her to get into the school she wants to attend, she said.
Still, she talks to groups about her struggles in the hope that she will help save someone, she says. She attends alumni meetings once a week and a several 12-step programs a week.
"I get to share where I was and where I am now to try to give kids hope," she said.