Adverse interactions between herbal and dietary substances and prescription medications: a clinical survey.

CONTEXT: Patients often combine prescription medications with herbal and dietary substances (herein referred to as herbal medicines). A variety of potential adverse herb-drug interactions exist based on the pharmacological properties of herbal and prescription medications.
OBJECTIVE: To determine the incidence of potential and observed adverse herb-drug interactions in patients using herbal medicines with prescription medications.
DESIGN: Consecutive patients were questioned about their use of herbal medicines in 6 outpatient clinics. Patients reporting use of these products provided a list of their prescription medications, which were reviewed for any potential adverse herb-drug interactions using a comprehensive natural medicine database. Any potential adverse herb-drug interactions prompted a review of the patient's chart for evidence of an observed adverse herb-drug interaction. MAIN OUTCOME MEASURE: The rate of potential and observed adverse herb-drug interactions.
RESULTS: Eight hundred four patients were surveyed, and 122 (15%) used herbal medicines. Eighty-five potential adverse herb-drug interactions were found in 49 patients (40% of herbal medicine users). Twelve possible adverse herb-drug interactions in 8 patients (7% of herbal medicine users) were observed. In all 12 cases, the severity scores were rated as mild, including 8 cases of hypoglycemia in diabetics taking nopal (prickly pear cactus).
CONCLUSIONS: A substantial number of potential adverse herb-drug interactions were detected and a small number of adverse herb-drug interactions observed, particularly in diabetics taking nopal. Screening for herbal medicine usage in 804 patients did not uncover any serious adverse interactions with prescription medications.