When the drug naltrexone is swallowed, it blocks the action of heroin for about two days. Australians first heard about naltrexone as a new treatment for heroin dependence in 1997.

In the late 1990s, Dr George O'Neil, a Perth obstetrician, became a strong advocate of naltrexone in the treatment of heroin dependence and established a growing clinical service to provide this treatment to the soaring numbers demanding it. Dr O'Neil began to recognise the limitations of depending on drug dependent patients to administer naltrexone to themselves. When only taken intermittently, naltrexone was not only ineffective but also dangerous. Dr O'Neil began producing naltrexone implants and then inserting these surgically into some thousands of patients.