Ans. is 'd' i.e., Methadone Maintenance therapy for opioid addiction* Once detoxification phase is over (i.e., withdrawal symptoms have been managed), the patient is maintained on any of the following drugs to prevent relapse by reducing craving and preventing 'kick' or 'euphoria' produced by opioids (morphine or heroin). Drugs used are : -1. Methadone: - Reduces craving and 'kick/euphoria from morphine or heroin because their opioid receptors are already occupied.2. LAAM and buprenorphine: - Similarly reduce craving.3. Opioid antagonists (naltrexone): - Naltrexone can be used orally to assist in the rehabilitation of ex-opioid abusers who are fully withdrawn (otherwise it induces an acute withdrawal syndrome). Naltrexone prevents relapse by discouraging substance seeking behavior - If a patient, who is on naltrexone maintenance therapy, takes an opioid, there is no 'kick' or euphoria as opioid receptors are already blocked. Naltrexone can be used with clonidine as in detoxification.Treatment of opioid addiction* Treatment can be divided into : -A. Treatment of toxicity (overdose)# Overdose is a medical emergency and is treated with opioid antagonist to reverse the complications (respiratory depression) by antagonizing the action on opioid receptors. Intravenous naloxone is the antagonist of choice for morphine (heroin) poisoning. Oral naltrexone is used for maintenance therapy, once acute poisoning has been treated by iv naloxone. Intravenous nalmefene is another specific antagonist.B. Treatment of dependence# Treatment of dependence include medically supervised withdrawal and detoxification, followed by maintenance therapy.a. Detoxification* Detoxification process include abrupt withdrawal of opioid followed by management of the emergent withdrawal symptoms, i.e., treatment of withdrawal syndrome. Detoxification can be done by any of the following.i) Substitution of long-acting opioid agonism : - Methadone is the treatment of choice. Because of its agonistic activity on opioid receptors it suppresses withdrawal symptoms. L-alpha-acetyl-methadol/ Levomethyl (LAAM) is the other opioid agonist which was used for this purpose. However it is no longer in use because some patients developed prolonged QT intervals (torsades de points).ii) Substitution of partial agonist: - Buprenorphine can be used in place of methadone because of its partial agonistic activity on opioid receptor.iii) Substitution by a2 agonists : - Clonidine as a sympatholytic agent due to its agonistic action on central presynaptic a2 receptors which reduce nor-adrenergic activity. Therefore, clonidine reduces the adrenergic withdrawal symptoms. Lofexidine, another a2 agonist, is an alternative to clonidine.iv) Clonidine plus naltrexone: - A more rapid detoxification can occur when clonidine is used along with naltrexone. Naltrexone, when given in opioid dependent patient, causes withdrawal symptoms because of its antagonistic action. These can be treated with clonidine. The addition of short acting Benzodiazepine (lorazepam or oxazepam) and NSAIDs, will help to relieve withdrawal symptoms not covered by clonidine. It should be kept in mind that naltrexone should not be used alone for detoxification (to treat withdrawal syptoms) as it precipitates or worsens the withdrawal syndrome.v) Other drugs : - Dextropropoxyphene, diphenoxylateb. Maintenance therapy:- explained above