"These pilot study findings showed that opiate-dependent injecting drug users with long injecting careers (most started between 1970 and 1982) and for whom opiate treatment had failed multiple times previously were attracted into and retained by therapy with injectable opiates."

Source

Metrebian, Nicky, Shanahan, William, Wells, Brian, and Stimson, Gerry, "Feasibility of prescribing injectable heroin and methadone to opiate-dependent drug users; associated health gains and harm reductions," The Medical Journal of Australia (MJA 1998; 168: 596-600).