KIRKWOOD • Bryan Gavan climbed the steps up to the stage at Kirkwood High School to tell the story of how his son became addicted to heroin as a teen and died three years later, a needle in his arm.

Later he would speak to students, but first he talked to parents. He told them he once thought as some of them probably do, that his child at a suburban high school couldn’t be using hard drugs.

Then he drug-tested his son after noticing changes in his behavior. Gavan prepared himself for alcohol or pot to show up in the results.

“I never considered what we were about to find out,” Gavan said. “We had absolutely no clue what we were dealing with.”

Heroin. When confronted, Klaeton Gavan told his father his addiction began with the painkillers a doctor prescribed after having wisdom teeth removed several months earlier. Soon it was heroin, which teens can now get for as little as $5 to $10.

It’s a story of addiction that counselors and advocates are trying to drive home. Users are all too often starting with painkillers and graduating to heroin. And they are doing it at an age when such drug use isn’t even on their parents’ radar.