Most pharmacy staff fail to point out potentially harmful herb-drug interactions when selling products containing St John’s wort, a secret-shopper experiment suggests.

A researcher from the University of Sydney’s School of Pharmacy went undercover in 109 Sydney pharmacies asking for the herbal preparation, telling pharmacists or floor staff it was for her “62-year-old mother who is a bit sad these days”.

St John’s wort (Hypericum perforatum) is a plant-derived complementary medicine used to treat mild mood disorders that is regulated by the TGA and is known to interact with a range of prescription medicines including psychotropics, antivirals, warfarin and ciclosporin.

If asked, the secret shopper or ‘pseudo-patient’ explained her mother was taking digoxin, verapamil and a sartan for an unspecified heart condition.