As dietary supplements gain widespread popularity for a number of preventive and treatment uses, researchers have sought to underline that their use, generally not reported to doctors, could lead to serious side effects when taken along with prescription medications.
But a team from the University of Pittsburgh looking at both the incidence and severity of potential interactions between prescription medications and dietary supplements in a US patient population found that most of the interactions - approximately 94 per cent- were not serious, based on limited available evidence. They report on the study in the latest issue of the Archives of Internal Medicine (164:630-636).
"This is encouraging news for the millions of patients currently taking prescription medications along with dietary supplements. However, limited information on drug-dietary interactions exists and health care providers should continue to inquire about dietary supplement use and consider the potential for interactions, regardless of their severity," said Lauren E. Trilli, assistant professor at the university's department of pharmacy and therapeutics.
The researchers surveyed 458 outpatients visiting two veterans affairs medical centers - one located in Los Angeles and the other in Pittsburgh. Because herbal supplements are more frequently used in the western half of the United States, the researchers wanted to compare results from a west coast and east coast location.
The survey participants were asked about their use of common herbal supplements, including chondroitin, coenzyme Q10, echinacea, garlic, gingko biloba, ginseng, glucosamine, saw palmetto, St. Johns Wort or vitamins. The data was cross-referenced with prescription of medications. Potential interactions were identified from various sources and medical searches.
All 458 patients surveyed were prescribed prescription medications, with an average of seven oral prescriptions per patient in Pittsburgh and six oral prescriptions per patient in Los Angeles. Of these patients, 197 or 43 per cent were taking at least one dietary supplement and the average consumption was three dietary supplements per day.
Among the patients taking supplements, 48 per cent of the Pittsburgh patients and 43 per cent of the Los Angeles patients had potential drug-dietary supplement interactions of any significance. Most patients had one or two possible drug-dietary supplement interactions, with seven patients in Pittsburgh and 12 in Los Angeles having more than three potential drug-dietary supplement interactions.
Most of the potential interactions found were with ginseng, garlic, gingko biloba and coenzyme Q.
"Our findings help provide a context for ongoing discussions about the risks of drug-dietary supplement interactions and raise concerns regarding subsequent adverse events," said Chester B. Good, associate professor of pharmacy and medicine at the University of Pittsburgh School of Medicine.
A much larger and broader patient sample is recommended for future studies to better quantify the incidence of potentially severe interactions and identify which persons may be at high risk for such events, he added.