Abstract Background People who use illicit opioids are more likely to be admitted to hospital than people of the same age in the general population. Many admissions end in discharge against medical advice, which is associated with readmission and all-cause mortality. Opioid withdrawal contributes to premature discharge. We sought to understand the barriers to timely provision of opioid substitution therapy (OST), which helps to prevent opioid withdrawal, in acute hospitals in England. Methods We requested policies on substance dependence management from 135 National Health Service trusts, which manage acute hospitals in England, and conducted a document content analysis. Additionally, we reviewed an Omitted and Delayed Medicines Tool (ODMT), one resource used to inform critical medicine categorisation in England. We worked closely with people with lived experience of OST and/or illicit opioid use, informed by principles of community-based participatory research. Results Eighty-six (64%) trusts provided 101 relevant policies. An additional 44 (33%) responded but could not provide relevant policies, and five (4%) did not send a definitive response. Policies illustrate procedural barriers to OST provision, including inconsistent application of national guidelines across trusts. Continuing community OST prescriptions for people admitted in the evening, night-time, or weekend was often precluded by requirements to confirm doses with organisations that were closed during these hours. 42/101 trusts (42%) required or recommended a urine drug test positive for OST medications or opioids prior to OST prescription. The language used in many policies was stigmatising and characterised people who use drugs as untrustworthy. OST was not specifically mentioned in the reviewed ODMT, with ‘drugs used in substance dependence’ collectively categorised as posing low risk if delayed and moderate risk if omitted. Conclusions Many hospitals in England have policies that likely prevent timely and effective OST. This was underpinned by the ‘low-risk’ categorisation of OST delay in the ODMT. Delays to continuity of OST between community and hospital settings may contribute to inpatient opioid withdrawal and increase the risk of discharge against medical advice. Acute hospitals in England require standardised best practice policies that account for the needs of this patient group.