As she spoke, tears spilled from her eyes. She wiped them with the cuff of her sweater, which covered track marks and a tattoo that said “freedom” — her goal, to be unshackled from the prison of addiction.

Ms. Harvey had been a popular honors student. But she developed anorexia. Alcohol was next. By 21, she was hooked on heroin.

In 2015, she was arrested on charges of prostitution. In an extraordinary act of contrition, she wrote a public apology online to her friends and family.

Still, she plunged in deeper. She estimated that at her worst, she was shooting up a staggering number of times a day, perhaps as many as 15 — heroin, cocaine, fentanyl. She overdosed five times. In Massachusetts, almost five residents die every day from overdoses.

“I don’t know how I’m alive, honestly,” Ms. Harvey said.

That night in October, she went into detox. Four days later, she checked out. She went back to her friends and drugs, developing an abscess on her arm, probably from dirty needles.

Two weeks later, she was back in detox. This time, she stayed, then entered a 30-day treatment program.

The return trips to detox have been an emotional roller coaster for her mother. To cope, Ms. Cavanagh founded a group, Magnolia New Beginnings, to help drug users and their families.