Research which said it is possible to live normally while regularly taking heroin has prompted a fierce debate.
The Glasgow Caledonian University study of 126 users of the class A drug found many were holding down normal jobs and relationships and passing exams.
However, Lord Victor Adebowale, the chief executive of specialist alcohol and drug organisation Turning Point, said the report was not saying that heroin was safe.
He explained: "It says that if you have a job, if you have a house, an income, are well educated and have a health system to support you, it's possible to survive an addiction to a pretty serious substance.
"Most people don't have this and have mental health challenges as well as a heroin problem."