ABSTRACTROSE M. AUCOIN. A Phenomenological Research Study of Peoples' Lived Experiences Related to Having a Sibling with Substance Use Problems. (Under the direction of DR. TARYNE M. MINGO) Research indicates that substance use of a family member can affect all members of the family (Church et al., 2018; Kelly et al., 2017; McDonagh et al., 2019). However, the major focus of research to date has been limited to the effects of substance use on the individual who presents with a substance use problem, their parents, their partners, and their children (Selbekk et al., 2018; Shumway et al., 2019). Leaving a gap in the literature related to sibling experiences with a siblings’ substance use. By broadening our view of who needs support when a family presents with an offspring suffering from substance misuse, researchers would help to support the thousands of siblings who are trying to manage their own lives while faced with the demands of their sibling’s addiction (Olafsdottir et al., 2020; Tsamparli & Frrokaj, 2016; Smith-Genthôs et al., 2017). The primary investigator used a phenomenological research design to explore the experiences of 15 participants who identify as having or having had a sibling with substance use problems. Semi-structured interviews and Interpretative Phenomenological Analysis were used to investigate the lived experiences of the participants related to having a sibling with substance use problems. The six themes identified were Safety, Chaos, Relationship Stress, Emotionality, Avoidance, and Movement. A review of implications and recommendations for clinicians and future research is included.