The document discusses the complex role of methadone in opioid substitution treatment, emphasizing its effectiveness as a long-term synthetic opioid that helps individuals transition from heroin. Methadone reduces withdrawal symptoms, minimizes the spread of infectious diseases, and lessens criminal behaviors associated with heroin use. It also highlights the challenges and comparisons with buprenorphine, noting methadone's status as the first-line treatment option recommended by NICE guidelines.