This article provides much-needed new insights into how patent medicines could enhance maternal power outside of clinical environments in the early twentieth century. While historians have considered the maternal management of domestic health, the role patent medicine products played in this complex equation of authority and expertise has yet to be the subject of sustained historical analysis. Using oral history archives, memoirs, social commentary, and advertisements, this article demonstrates how the expertise that mothers possessed was multifaceted, with powerful spatial, temporal, and even commercial connotations. This influence was especially significant at a time when clinical environments were still largely dominated by men, when the home was increasingly invaded by experts and expertise, and when dependants of wage earners were not covered by welfare provisions such as the 1911 National Insurance Act. © 2020 The Author(s) [2020]. Published by Oxford University Press. All rights reserved.