Opioid Substitution Treatment (OST) is a harm reduction strategy enabling opiate consumers to avoid withdrawal symptoms and maintain health and wellbeing. Some research shows that within a disaster context service disruptions and infrastructure damage affect OST services, including problems with accessibility, dosing, and scripts. Currently little is known about planning for OST in the reduction and response phases of a disaster. This study aimed to identify the views of three professional groups working in Aotearoa/New Zealand about OST provision following a disaster. In-depth, semi-structured interviews were conducted with 17 service workers, health professionals, and emergency managers in OST and disaster planning fields. Thematic analysis of transcripts identified three key themes, namely “health and wellbeing”, “developing an emergency management plan”, and “stock, dose verification, and scripts” which led to an overarching concept of “service continuity in OST preparedness planning”. Participants viewed service continuity as essential for reducing physical and psychological distress for OST clients, their families, and wider communities. Alcohol and drug and OST health professionals understood the specific needs of clients, while emergency managers discussed the need for sufficient preparedness planning to minimise harm. It is concluded that OST preparedness planning must be multidisciplinary, flexible, and inclusive.