Objectives Informal caregivers experience daily hassles – a form of persistent stress, as a consequence of caregiving. This study aimed to develop and test a new theoretical model of health information‐seeking behaviour, the Knowledge Hassles Information Seeking Model (KHISM). KHISM hypothesized that the knowledge hassles of caregivers – daily stressors experienced while dealing with tasks which require knowledge about the safety and effectiveness of the care‐recipients' medicines – would influence caregivers' willingness to assist their care‐recipient to use an Australian medication management service, Home Medicines Review (HMR). Methods A cross‐sectional postal survey was conducted among 2350 members of Carers (NSW, Australia). Respondents were included in the study if they were involved in medication‐related tasks for their care‐recipient and were not paid as caregivers. Also, their care‐recipient needed to be taking more than five medicines daily or more than 12 doses daily and had not yet experienced HMR. Structural equation modelling was used to test the model. Results A total of 324 useable surveys were returned yielding a response rate of 14%. Respondents were quite willing to assist their care‐recipient to use HMR (willingness). The model predicted 51% of the variation in willingness. Knowledge hassles increased positive outcome expectancy (β = 0.40, P < 0.05) and indirectly increased willingness. Conclusions The more caregivers experience hassles with medication knowledge, the more they perceive HMR to be a helpful information source and the more willing they are to use it. Targeted marketing centred on HMR as an information source may increase caregivers' demand for HMR. Further exploration of the phenomenon of knowledge hassles is warranted.