This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Psychiatry
The drug which is used for long-term maintenance in opioid addiction - 
Select and explain. 
A. Naloxone, B. Nalorphine, C. Butarphanol, D. Methadone
D: Methadone
Answer: D: Methadone 
Explanation: Drugs for long-term maintenance for opioid dependence (addiction) :- Methadone is the DOC. Alternatives are buprenorphine, LAAM, opioid antagonists (naltrexone).