Substance use disorders (SUD) are a type of mental illness where a person cannot control their use of drugs, alcohol, and/or medications [1]. Worldwide, around 35 million people are affected by SUD [2, 3]. However, long wait times to enter treatment and geographical constraints means many people are without access to help [4]. eHealth products, such as websites and mobile applications, present an opportunity for people with SUD to receive flexible, tailored support that may overcome the barriers of traditional treatment methods [5, 6]. User Experience (UX) research, which aims to improve the usability and satisfaction of a product, could be a consumer-centric way to improve the use and efficacy of eHealth products [7]. However, UX research that considers SUD eHealth is limited. In addition, current design guidelines in industry are broad or address other health conditions: a design resource for SUD does not exist. There is therefore a research gap in understanding how interfaces can be better designed for this audience. This ongoing research project explores the challenges people with SUD may face in accessing support and information online, and how SUD eHealth products could be designed to mitigate these effects. Preliminary findings from expert interviews with SUD clinicians suggest effects relating to memory, attention, and personal device access could all impact how someone with SUD uses a digital interface. These findings, plus those from planned research activities, could help formulate a new design resource that could create better interfaces for SUD eHealth products.