Indeed, opioid substitution treatment (OST) has been shown to be the most effective treatment for chronic heroin dependence in both community, [23][24][25] and prison setting. [26][27][28] OST is treatment of heroin dependence with opioid agonists (methadone) or opioid partial agonists (buprenorphine and buprenorphine-naloxone) which can be offered as a short-term detoxification or long-term maintenance treatment. Research has shown that OST is substantially more effective when offered on a long-term basis. 29,30 When administered at therapeutic doses (methadone >60ml, buprenorphine and buprenorphinenaloxone >8mg), OST has been shown to significantly reduce heroin use, HIV/HCV seroconversion, injecting drug use, overdose deaths and engagement in criminal activities. [31][32][33] Additionally, it notably improves treatment retention, general health, employment stability, social functioning and overall quality of life. 34,35 Due to their proven effectiveness, World Health Organisation, 36 includes methadone and buprenorphine on the list of essential medicines and recommends them to be available to people by all health systems and governments. WHO also provides clear directives that provision of essential medicines and healthcare services should be of the same standard in prisons and community. 36,37 Despite both WHO, 36 and United Nations Office on Drugs and Crime, 38 recommending OST in prisons as primary treatment for heroin dependence and essential intervention for HIV prevention,