"They ought to say: `who else lives in your household? Are they helping and do you want them to help?'," Prof Pauline Norris, who holds a chair in social pharmacy in the university's School of Pharmacy, said at a seminar in Dunedin this week.
Prof Norris is one of a team of researchers analysing many aspects of the use and misuse of medications in everyday life.
The medications being studied include vitamins, dietary supplements, alternative medicines, over-the-counter remedies and prescriptions.
The "enormous project" involved interviewing members of 57 households about what medications were kept in the house, where and how they were stored, how they were used, how they felt about medicines, and what influenced them to take medicines, she said.
Household members were also asked to keep diaries for a week listing what medicines they noticed in advertisements and retail outlets, and what medications they took.
Prof Norris then looked more closely at how relationships between the members of 15 households where at least one person was caring for the health needs of another, influenced prescription medicine-taking decisions.
While she found family members, carers or flatmates could assist medicine takers in several ways, they could also influence patients not to take medications.
Sometimes, parents or carers looking after children or elderly people chose not to administer a prescription medicine, or to administer less than the recommended dose.
It would be useful for health professionals to consider such influences, she said.
Households members were also asked to collect and show all medicines stored at home.
Prof Norris said she was stuck by the large number of prescription medicines people kept and the number of people who had prescription medicines dating back 20 years or more.