This study contributes to the information systems literature on mobile health interventions and omnichannel management by examining the relative effectiveness of mobile and offline channels in facilitating personal weight management. Drawing on the social cognitive theory of self-regulation, our empirical analysis utilizes a system generalized method of moments approach applied to panel data on customers enrolled in a weight loss program that delivers services through multiple channels, including a mobile app and offline office visits. Our results show that the use of the mobile app is positively associated with weight management by both free and paid users. For paid users, who have access to the mobile app and office visits, usage of both channels is associated with increased shortterm weight loss. Furthermore, the two channels function as substitutes for one another, with users able to compensate for infrequent offline store visits through more intense mobile app usage. In the long term, however, only mobile app usage (and not offline store visits) contributes to the sustainability of weight loss, as reflected in reduced weight variability and lower overall failure rate. Qualitative evidence gleaned from interviews with actual customers substantiated the self-regulation mechanism enabled by mobile app usage. Additional empirical analyses further revealed that frequency and granularity of mobile app usage are positively associated with weight loss. We also found that individuals exposed to low performance pressure benefit more fully from mobile app usage. The results are robust to endogeneity concerns and alternative measures of the key variables. Overall, our analysis sheds light on the important role of a self-regulatory mobile app in a multichannel setting of personal weight management, as compared with the external influence stemming from human experts in offline channels, with useful implications for research and practice.