GLASGOW — Tony Nugent was clean for almost seven years before he relapsed.

He found that heroin, cruel to the young, is even less forgiving with age.

Mr. Nugent had been using the drug on and off since he was 19, but overdosed the first time he shot up again. He has overdosed three more times since last year.

“I’ve nearly died four times,” said Mr. Nugent, who turns 43 this month. “It’s getting harder for me to recover as I get older.”

Still, he considers himself lucky, especially living in what is now being called the “drug-death capital of the world.”