Assessing Natural Health Product-Drug Interactions and Coding Feasibility: Analysis of a New Zealand General Population Dataset from an Online Market Research Panel

INTRODUCTION: Natural health products (NHPs) include complementary/alternative medicines, dietary supplements, nutraceuticals, and traditional medicines. Natural health products are often self-prescribed and used alongside conventional medicines, raising safety concerns. AIMS: This study aims to explore NHP-conventional medicine (NHP-drug) combinations used by respondents in New Zealand (NZ), identify those with the potential to cause NHP-drug interactions, and assesses the feasibility of coding NHPs using the WHODrug dictionary. METHODS: A dataset from a pilot study on NHP use in NZ was analysed. Data on NHP and conventional medicine use were descriptively analysed. Where possible, specific product ingredient lists were verified. Two coders independently assigned WHODrug Global codes to each NHP and conventional medicine. Fleiss' Kappa measured inter-coder agreement. RESULTS: Of 992 participants, 381 (38.4%) were current NHP users, reporting 1-18 NHPs. Among them, 271 (71.1%) used conventional medicines concurrently. Natural health product-drug combinations with potential interactions were found with fish oil, coenzyme Q10, turmeric, and glucosamine. An interaction involving fish oil and warfarin was rated as 'may result in significant hazard.' One-third (33.1%) of NHPs could not be coded using WHODrug. Codability agreement was higher for conventional medicines (93.7%) than for NHPs (63.5%). Fleiss' Kappa indicated moderate agreement for NHPs (κ = 0.576) and very good agreement for conventional medicines (κ = 0.911). CONCLUSION: Substantial concurrent NHP-drug use was identified, including combinations with potential adverse reactions. A larger, nationally representative dataset on NHP exposures in NZ is needed. Current challenges in coding NHPs highlight the need for standardised, comprehensive coding tools in future research for comprehensive analysis.