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Study Finds Little Effects in Patients Who Take Prescription Drugs and Dietary Supplements

PITTSBURGH, March 22, 2004 – While the use of dietary supplements appears to be very common among patients who also take prescription medications, researchers at the University of Pittsburgh found that most potential drug-dietary supplement interactions were not serious. Results of their findings are in today's Archives of Internal Medicine.

Dietary supplements have been gaining widespread popularity to treat a myriad of health conditions and physical complaints. However, the extent of this use along with prescription medications is widely unknown or underreported by primary care physicians.

The Pitt researchers sought to explore both the incidence and severity of potential interactions between prescription medications and dietary supplements and found that most of the interactions – approximately 94 percent of the patient population studied – were not serious, based on limited available evidence.

"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," says Lauren E. Trilli, PharmD., B.C.P.S., assistant professor, department of pharmacy and therapeutics, University of Pittsburgh School of Pharmacy and a clinical pharmacy specialist at the Pittsburgh VA Healthcare System.

The researchers surveyed 458 outpatients visiting general medicine clinics at two veterans affairs medical centers located in Los Angeles and Pittsburgh. Because herbal supplements are more frequently used in the western half of the United States, the researchers sought to sample one VA health care system on the West Coast and compare results with a VA health care system on the East Coast.

The survey participants were asked whether they have ever taken in the past, or were currently taking the following herbal supplements: Chondroitin, Coenzyme Q, DHEA, Echinacea, Garlic, Gingko biloba, Ginseng, Glucosamine, Melatonin, Saw Palmetto, St. Johns Wort, vitamin, or other.

The researchers cross-referenced self-reported use of dietary supplements with prescription of medications by VA health care providers, and 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 percent were taking at least one dietary supplement and the average consumption was three dietary supplements per day. Pharmacies and grocery stores were the most common places of purchase of dietary supplements. A monthly expenditure of less than $25 on supplements was reported by 83 percent of the patients surveyed from Pittsburgh and 72 percent of the patients surveyed from Los Angeles. The most common reported sources of information regarding dietary supplements were friends or relatives and books or magazines.

Among the patients taking supplements, 48 percent of the Pittsburgh patients and 43 percent 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 7 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. In future studies, we recommend a much larger and broader patient sample to better quantify the incidence of potentially severe interactions and identify which persons may be at high risk for such events," added Chester B. Good, M.D., M.P.H., associate professor of pharmacy and medicine, department of internal medicine at the University of Pittsburgh School of Medicine and staff physician at the Pittsburgh VA Healthcare System.

Collaborating with Drs. Trilli and Good are Peter A. Glassman, M.B.B.S., M.Sc., division of general internal medicine, Veterans Affairs Center, Greater Los Angeles; Jocelyn Hayes-Hunter, PharmD., University of California Los Angeles (UCLA) School of Pharmacy; and Catherine Peng, PharmD., B.C.P.S., from the Veterans Affairs Palo Alto Health Care System.

Source: University of Pittsburgh Medical Center

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