Opioid use disorder (OUD) is highly prevalent among persons who are incarcerated. Medication treatment for opioid use disorder (MOUD), methadone, buprenorphine, and naltrexone, is widely used to treat OUD in the community. Despite MOUD's well-documented effectiveness in improving health and social outcomes, its use in American jails and prisons is limited.Several factors are used to justify limited access to MOUD in jails and prisons including: "uncertainty" of MOUD's effectiveness during incarceration, security concerns, risk of overdose from MOUD, lack of resources and institutional infrastructure, and the inability of people with OUD to provide informed consent. Stigma regarding MOUD also likely plays a role. While these factors are relevant to the creation and implementation of addiction treatment policies in incarcerated settings, their ethicality remains underexplored.Using ethical principles of beneficence/non-maleficence, justice, and autonomy, in addition to public health ethics, we evaluate the ethicality of the above list of factors. There is a two-fold ethical imperative to provide MOUD in jails and prisons. Firstly, persons who are incarcerated have the right to evidence-based medical care for OUD. Secondly, because jails and prisons are government institutions, they have an obligation to provide that evidence-based treatment. Additionally, jails and prisons must address the systematic barriers that prevent them from fulfilling that responsibility. According to widely accepted ethical principles, strong evidence supporting the health benefits of MOUD cannot be subordinated to stigma or inaccurate assessments of security, cost, and feasibility. We conclude that making MOUD inaccessible in jails and prisons is ethically impermissible.