A large number of prisoners come to jail with significant drug habits and that does not end the moment they get to their cells. In fact, Barlinnie is the largest single supplier of methadone in Europe.  

A lot of hard work goes into rehabilitating  addicts before their release, but this is hampered by the smuggling of a steady flow of drugs into the prison.   

A 20 feet high wall topped with razor wire is designed to butcher anyone who tries to escape and while it is an effective barrier to anyone trying to get out, it does not stop drugs getting in. Drugs are thrown over the wall, and picked up by a pre-arranged prisoner. It is a risky strategy, with cameras constantly watching the area. 

Cannabis, cocain, ecstasy, heroin and others also arrive in the jail hidden in  the visiting time kiss, or concealed in books and games.