The correct option is
D All of the above
Methadone is a synthetic opiate and sold under the name dolophine. Opiates are considered as the king of narcotics. They bind to specific receptors in brain and affect many functions of body like slowing down respiration, decreased glandular secretions, nausea and vomiting etc. It is used as analgesic (pain killer). It is also used for deaddiction of morphine and heroin as it prevents the withdrawal symptoms associated with opiates.
So, the correct answer is 'All of the above'.