John once fielded customer complaints for a telecommunications company. Now he usually hangs out with friends in the courtyard of a center offering services to help people who use drugs, hitting his pipe, or as he calls it, “getting methicated.”

He usually lives outdoors, though he can sometimes handle a few days at a shelter. By noon, he tries to stop smoking meth, so he can get to sleep later that night. Quitting is not on his radar: meth rules his life. “We cannot ride on the railroad, the railroad rides upon us,” he said, with a nod to Henry David Thoreau.

Most weekdays, Bill Burns, an addiction and mental health specialist with the Portland police, walks the Bayside neighborhood, checking in on folks. On Thursdays, he rewards the regulars he drives to addiction treatment clinics with his own homemade jolts of dopamine: sugar-dense, Rice Krispie-style treats.

Recently, he encountered a young man in full meth psychosis, wild-eyed, bare-chested and bleeding, flinging himself against concrete barriers in an alley. Mr. Burns slipped between the man and a brick wall and wrapped his arms protectively around him.