UNLABELLED: Due to the global rise in the popularity of herbal medicines, adversities resulting from concomitant use of both prescription drugs and herbs are becoming an increasingly important public health issue. OBJECTIVES: To estimate the prevalence of the use of herbal medicines among persons on prescription medicines in Jamaica. Findings are thought to aid in estimates of the risk of adversities from drug-herb interactions through laboratory investigations and to provide awareness among policy makers responsible for the design of appropriate pharmacovigilance systems in the country. METHODS: A survey was conducted in eighteen pharmacies throughout Jamaica and patients or parents/carers of children who were on at least one prescription medicine were administered a structured questionnaire by trained interviewers. RESULTS: Of 399 persons invited to participate in the study 365 (91.5% response rate) agreed to do so and were included in the study. This study population consisted of 306 adults and 60 children and of that 243 adults (80.6%) and 45 children (75.6%) engaged in the concomitant use of herbs and drugs. Patients with a variety of disease conditions, in both rural and urban environs engaged in concomitant herb-drug use. Persons with higher salary (P<0.1) and those with health insurance (P<0.02) tended to have a lower prevalence of herb-drug concomitant use. Among persons indicating such practices the most commonly cited reason for concurrent use of prescription medicine and herbal preparations was the belief that there was no harm in taking both (269, 94.0%) followed by the belief that the prescription medicine alone was not adequate cure (211, 71%). Only 55 (18%) respondents who practised such co-medication indicated that their doctors knew of their use of herbal preparations. CONCLUSION: There is a high prevalence of herb-drug concomitant use in Jamaica, and an awareness within the medical community and those monitoring adversities would serve well to mitigate risks from potential drug-herb interactions.