AbstractIn order to be able to provide thorough and timely coverage on the most recent scientific research, science journalists frequently rely on embargoed information sent to them by publishers of scientific journals. In such embargo e-mails, publishers purposefully bring selected upcoming releases to the journalists’ attention a few days in advance of their publication. Little is known on how this early highlighting of certain research articles affects their later citations or altmetrics. We present an exploratory case study with the aim of assessing the effects of such promotion activities on scientific articles’ bibliometric and altmetric indicators. In a treatment–control design, we analyze citation counts and eight types of altmetrics of 715 articles published between 2016 and 2017 whose DOIs have been mentioned in embargo e-mails and compare these to articles from the same journal issues that have not been highlighted in embargo e-mails. Descriptive statistics and Mann–Whitney-U tests reveal significant advantages for promoted articles across all regarded metrics three to four years after their publication. Particularly large differences can be seen regarding numbers of mentions in mainstream media, in blogs, on Twitter, and on Facebook. Our findings suggest that scholarly publishers exert significant influence over which research articles will receive attention and visibility in various (social) media. Also, regarding utilizations of metrics for evaluative purposes, the observed effects of promotional activities on indicators might constitute a factor of undesirable influence that currently does not receive the amount of consideration in scientometric assessments that it should receive.