There is considerable uncertainty regarding medication use during breastfeeding. This study compared lactation-related questions about medicines from consumers and health professionals to identify knowledge gaps. A retrospective, mixed-methods study of lactation-related call data extracted from two Australian medicines call centre databases: National Prescribing Service (NPS) Medicines Line (ML) for the general public and Therapeutic Advice and Information Service (TAIS) for health professionals, was conducted. Of the 5662 lactation-related calls by consumers to ML, most were from women enquiring about themselves (95%). The 2219 lactation-related calls from health professionals to TAIS were largely from GPs (46%), community pharmacists (35%) and nurses (12%). Consumers commonly enquired about medicines freely accessible or over-the-counter, including non-steroidal anti-inflammatory products (9.3%), paracetamol (6.9%), ibuprofen (4.8%) and codeine (4.2%). Health professionals' questions involved prescription medicines such as antidepressants (16.9%), with queries on sertraline (3.7%), levonorgestrel (2.7%) and domperidone (2.4%) most common. Question themes were similar for both cohorts, focusing mainly around medication safety, risk minimisation and milk supply. Understanding the compelling and common themes driving medicines help-seeking related to breastfeeding is key to addressing information gaps and improving overall medication use during breastfeeding.