Galactagogues are foods, herbs or medications thought to support or increase breast milk supply. The use of galactagogues during lactation is becoming increasingly common despite limited evidence regarding effectiveness and safety, and no definitive recommendations for use in clinical practice. The aim of this study is to explore factors influencing women’s decisions to use galactagogues during lactation. Twenty-two semi-structured interviews were conducted in October and November 2019 (over the telephone or in person) with participants located in most Australian states and territories, including metro and regional areas. Interviews were audio-recorded, transcribed verbatim and thematically analysed using NVivo. Analysis revealed that following a concern about breast milk supply, the decision to use galactagogues was influenced by three core and interrelated domains: access to and quality of breastfeeding support, maternal agency and determination to provide breast milk. Women revealed many problematic experiences with health care professionals that left them feeling dismissed and confused due to provision of inconsistent and insufficient information that was sometimes at odds with their desire to provide breast milk. In this instance, some women turned to galactagogues to regain agency. A range of broader dimensions influencing decision-making also emerged. These were separated into categories that emphasise distinctions relating to breast milk supply, which included: maternal emotional wellbeing, social norms and pressures, concerns about infant development, maternal physical health and lactation history, as well as those relating specifically to galactagogue use, including: desire for a guaranteed/urgent response, risk-risk trade-off, acceptance and trust, and accessibility and cost. In understanding the complexity of decision-making concerning these substances, we identify opportunities to improve breastfeeding counselling and support. We recommend that support be individually tailored to manage conflicting information, adopt communication styles that encourage trust and processes that enable shared decision-making to enhance or restore maternal agency. There is also considerable need to address evidence gaps regarding the effectiveness and safety of commonly used galactagogues, so that women can be appropriately counselled about potential benefits and harms.