Since 2014, the United Nations Office on Drugs and Crime (UNODC) - World Health Organization (WHO) Informal Scientific Network (ISN) has brought the voice of science to international drug policy discussions, especially at the Commission on Narcotic Drugs (CND), the drug-control policy-making body of the United Nations (UN). The public health dimension of the world drug problem, including prevention and treatment of substance use disorders (SUDs), has become prominent in policy debates within the UN system1. Many people in the criminal justice system have a history of SUDs and other mental health conditions. An estimated one in three people in prison have used drugs during incarceration2. The worldwide prison population stands at 11.2 million individuals3, and continues to increase. This and related prison overcrowding have profound implications for the physical and mental health of people in incarceration and the well-being of their families and communities. If people with SUDs engage in criminal activities, these are often minor offences driven by the need to support their substance use4. Imprisonment is not an effective response to substance use/SUDs5, and it may exacerbate pre-existing problems. SUDs should be treated as health conditions and not as criminal behaviors. It is essential to provide accessible, evidence-based SUD treatment in the community and establish different non-custodial measures, including SUD treatment as an alternative to conviction or punishment for people with SUDs in contact with the criminal justice system. In case of personal-use-related drug offences and other minor offences by people with SUDs, countries should redirect them toward health care and social services instead of applying ineffective punitive measures. This approach aligns with the UNODC-WHO International Standards for the Treatment of Drug Use Disorders4 and the International Drug Control Conventions, the UN Standards Minimum Rules for the Treatment of Prisoners6, the UN Standard Minimum Rules for Non-Custodial Measures7, as well as the UN Rules for the Treatment of Women Prisoners and Non-Custodial Measures for Women Offenders8. When the severity of the crime precludes the consideration of treatment as an alternative to conviction or punishment, countries need to ensure access to SUD treatment within prison settings and ensure continuity of treatment in line with services provided in the community. Offering treatment and care in prison settings corresponds to the CND resolution 61/7 on "Addressing the specific needs of vulnerable members of society in response to the world drug problem"9 and the 2016 UN General Assembly Special Session on Drugs Outcome Document1. Treatment for SUDs based on evidence has been shown to be critical in reducing substance use, overdose, reoffending and reincarceration in populations with a history of involvement with the justice system. Treatment and care interventions in line with UNODC-WHO International Standards can contribute towards supporting both the welfare of the community and the promotion of personal recovery. To ensure that all individuals with SUDs who come into contact with the criminal justice system, including those in prison, receive the same level of care, respect and dignity, the ISN is urging UN Member States to change their response to SUDs from a criminal justice to a public health strategy.