BackgroundThere is emerging evidence that stimulants warrant further investigation as a treatment for bulimia nervosa (BN) including a recent open-label feasibility trial examining the use of lisdexamfetamine dimestylate (LDX) for BN. The current report presents the secondary outcomes and qualitative interview results from that feasibility trial. These outcomes explore several purported mechanisms that may explain how stimulants affect symptoms of BN: appetite, impulsivity, obsessive and compulsive symptoms, eating disorder psychopathology/impairment and reward-based decision-making.MethodsTwenty-three participants with BN received LDX for eight weeks. Questionnaires assessing appetite, impulsivity, obsessive and compulsive symptoms, eating disorder psychopathology and impairment were administered at baseline and post-treatment. Participants also completed a two-step reinforcement learning task to assess their decision-making. Semi-structured interviews took place at baseline, week 5, and follow-up.ResultsReductions in hunger, food-related impulsivity, obsessive and compulsive features, eating disorder psychopathology and impairment were found. However, reward learning, as far as it is assessed by the task, did not seem to contribute to the effect of LDX on BN symptoms. Qualitative analysis suggested four themes: (1) reprieve from the eating disorder, (2) improvement in function and quality of life, (3) renewed hope for recovery, and (4) ability to normalize eating.ConclusionsThis report suggests several potential mechanisms by which LDX may reduce symptoms of binging and purging in those with BN. Importantly, due to the open-label design, we are unable to attribute findings to the medication. Instead, our results should be interpreted as hypothesis generating to inform future studies such as adequately powered randomized controlled trials.Trial registrationNCT03397446.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40337-023-00796-x.