Which of the following is a semi-synthetic substitute considered a narcotic?

Methadone is recognized as a semi-synthetic substitute that is classified as a narcotic. It is synthesized from natural opiates and is utilized primarily in the treatment of opioid addiction and for pain management. Being a semi-synthetic opioid, methadone mimics the effects of natural opioids while also possessing properties that help mitigate withdrawal symptoms and cravings associated with opioid dependence.

In contrast, heroin is a fully synthetic narcotic, while marijuana and cocaine are classified differently. Marijuana is derived from the cannabis plant and contains cannabinoids, making it distinct from traditional narcotics. Cocaine is a stimulant derived from the coca plant, not a narcotic in the same sense as methadone or other opioids. Thus, methadone stands out as the option that fits the criteria of being a semi-synthetic narcotic substitute.