Online brand communities often use social plug-in features, such as the Like button, to facilitate social interactions and engage users with the brands. However, whether and how such a community feature affects users’ purchases remain open questions. Analysis of user behavior following the adoption of the Like feature indicates a surprising downturn in purchases, with a 4.1% decrease in orders and a 25.0% reduction in expenditure. Notably, online purchases dip by 3.4% in order numbers and 21.1% in expenditure, with a slighter offline decrease. The treatment effect of the adoption is not always negative but varies over time and across users. First, the Like feature adoption has a positive effect on users’ purchases in the first two months (primarily through enhancing their community participation), and the treatment effect turns negative in subsequent months, leading to the overall negative treatment effect on purchases. Second, the negative treatment effect likely stems from unflattering social comparison and can become weaker or even positive when users accrue more Likes. However, only a small proportion of users receive sufficient Likes to be motivated to purchase more. Our results caution against potential downsides of the Like feature in online communities and provide valuable managerial implications.