Methadone was first developed during the Second World War in Germany as an alternative to heroin when it was feared the country's supply lines of the opium poppy might be destroyed.

German doctors used it as an analgesic. From the 1950s on in the United States, it was used to treat patients for the pain associated with terminal illnesses like cancer.

In 1964, two scientists in the United States -- psychiatrist Dr. Marie Nyswander and medical researcher Dr. Vincent Dole of Rockerfeller University in New York, developed a way of using methadone as a tool for the treatment of heroin addicts.

Initially, methadone had to overcome serious opposition from lawmakers, journalists and doctors in the United States who reviled its addictive properties.

There were also side effects from its usage such as constipation, skin rashes and insomnia. However it was clear that the pre-1960s approach to heroin addiction in the United States -- admitting addicts to federally funded facilities where they were given gradually lower doses of heroin and then methadone until they were drug free or detoxified -- was an abysmal failure.

People so treated became locked into a perpetual state of heroin addiction followed by detoxification and then a relapse which never ended.

Treatment centres like Addiction Services say methadone has several advantages. It has a long lasting effect and need only be taken once a day.

Typically, an addict must get a hit every four to six hours or else he experiences painful withdrawal symptoms. Methadone also blocks the effects of heroin thus making the purchase of the drug by an addict less likely.

Often methadone is mixed with an orange drink (hence the slang term "the juice'') before it is taken.

In many ways, the use of methadone as a tool for treating addicts has led to a shift in the popular definition of a heroin user as a "junkie'' or "criminal''. He became an "addict,'' essentially a person with a heroin dependency in need of intense therapy, counselling and other support.